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  • Comparative evaluation of UNEX-based DNA extraction for molecular detection of Cyclospora cayetanensis, Toxoplasma gondii, and Cryptosporidium parvum as contaminants of berries
    Food Microbiol. (IF 4.089) Pub Date : 2020-01-26
    Tamirat Tefera Temesgen; Alessandra Barlaam; Kristoffer R. Tysnes; Lucy J. Robertson

    The potential public health impact of foodborne parasites transmitted via contaminated fresh produces indicates the necessity for robust and reliable laboratory methods for their detection and identification on this infection vehicle. Standardization of methods for detection of common FBP in fresh produce is to be expected and ensuring that the DNA extraction approach is most appropriate for the FBP of interest and for the matrix being analyzed is also important. Therefore, the aim of the present study was to compare the efficacy of two commercially available DNA extraction procedures, the UNEX-based method and DNeasy PowerSoil kit in the detection of three protozoan parasites, C. cayetanensis, C. parvum, and T. gondii, on contaminated berries. Oocysts of each parasite were spiked into the pellets of raspberry and blueberry washes. The spiked pellets were then randomly assigned to DNA extraction using either the PowerSoil or UNEX method, with DNA extraction with both methods performed by two independent analysts. The detection rate when berry washes were spiked with 20 oocysts of C. cayetanensis, T. gondii, and C. parvum was 95%, 85%, and 40%, respectively, when using the PowerSoil kit; whereas the equivalent results using the UNEX method were 55%, 60%, and 5%, respectively. In addition, significantly lower Cq values were achieved for each parasite in the samples spiked with 500 oocysts when the PowerSoil kit was used. Possible reasons for these results are discussed, and include the composition of both the beads and the buffers in each method.

  • Addition of volatile sulfur compounds to yeast at the early stages of fermentation reveals distinct biological and chemical pathways for aroma formation
    Food Microbiol. (IF 4.089) Pub Date : 2020-01-24
    Matias I. Kinzurik; Rebecca C. Deed; Mandy Herbst-Johnstone; Davide Slaghenaufi; Raffaele Guzzon; Richard C. Gardner; Roberto Larcher; Bruno Fedrizzi

    Volatile sulfur compounds (VSCs) greatly influence the sensory properties and quality of wine and arise via both biological and chemical mechanisms. VSCs formed can also act as precursors for further downstream VSCs, thus elucidating the pathways leading to their formation is paramount. Short-term additions of exogenous hydrogen sulfide (H2S), ethanethiol (EtSH), S-ethylthio acetate (ETA), methanethiol (MeSH) and S-methylthio acetate (MTA) were made to exponentially growing fermentations of synthetic grape medium. The VSC profiles produced from live yeast cells were compared with those from dead cells and no cells. Interestingly, this experiment allowed the identification of specific biochemical and/or chemical pathways; e.g. most of the conversion of H2S to EtSH, and the further step from EtSH to ETA, required the presence of live yeast cells, as did the conversion of MeSH to MTA. In contrast, the reaction from MTA to MeSH and ETA to EtSH was due primarily to chemical degradation. Ultimately, this research unravelled some of the complex interactions and interconversions between VSCs, pinpointing the key biochemical and chemical nodes. These pathways are highly interconnected and showcase the complexity of both the sulfur pathways in yeast and the reactive chemistry of sulfur-containing compounds.

  • Prevalence and Genetic characteristics of Cronobacter spp. from Food and Human Clinical Stool Samples in Wenzhou, China 2008-2018
    Food Microbiol. (IF 4.089) Pub Date : 2020-01-22
    Yi Li; Leyi Zhang; Yuqin Hu; Chengji Hong; Airong Xie; Yuejin Wu; Zhihui; Shangguan; Lingling Mei; Biao Zhou; Yanjun Zhang; Lei Fang

    Pathogenic Cronobacter species are responsible for life-threatening illness in neonates. A ten-year comprehensive survey was conducted to examine the population structure and antimicrobial resistant patterns of Cronobacter isolates from food (n=78) and clinical (n=12) sources in Wenzhou, China. A total of 90 (4.4%) isolates were recovered from 2051 collected samples. The occurrence of Cronobacter spp. was highest in spices with a rate of 22% (26/119), whereas the lowest contamination rate of 1% was found in powered infant and toddler formula (7/494), special medical infant formula (1/95) and human stool samples (12/1024). Cronobacter strains revealed a high degree of genetic diversity among the isolates tested. Pulsed-field gel electrophoresis (PFGE) distinguished 75 clonal groups, and the biggest cluster consisted of four strains. Multilocus sequence typing (MLST) method displayed 43 sequence types (STs), of which ST1, ST4, ST8, ST64, ST148 and ST201 were most frequently identified. Meanwhile, two new sequence types were discovered and added to the PubMLST international database. Resistance to ceftriaxone, cefotaxiv, amoxicillin, ampicillin, cefoxitin, tetracycline, streptomycin, azithromycin, chloramphenicol, as well as multidrug resistance, was noted. Taken together, this large-scale surveillance study highlights the wide dissemination and diverse molecular features of Cronobacter spp. in Wenzhou China.

  • Raw meat quality and salt levels affect the bacterial species diversity and community dynamics during the fermentation of pork mince
    Food Microbiol. (IF 4.089) Pub Date : 2020-01-21
    Christina Charmpi; David Van der Veken; Emiel Van Reckem; Luc De Vuyst; Frédéric Leroy

    Acidification level and temperature modulate the beneficial consortia of lactic acid bacteria (LAB) and coagulase-negative staphylococci (CNS) during meat fermentation. Less is known about the impact of other factors, such as raw meat quality and salting. These could for instance affect the growth of the pathogen Staphylococcus aureus or of Enterobacterales species, potentially indicative of poor fermentation practice. Therefore, pork batters from either normal or borderline quality (dark-firm-dry, DFD) were compared at various salt concentrations (0-4%) in meat fermentation models. Microbial ecology of the samples was investigated with culture-dependent techniques and (GTG)5-PCR fingerprinting of genomic DNA. Whilst Lactobacillus sakei governed the fermentation of normal meat, Lactobacillus curvatus was more prominent in the fermentation of the DFD meat variant. CNS were favoured during fermentation at rising salt concentrations without much effects on species diversity, consisting mostly of Staphylococcus equorum, Staphylococcus saprophyticus, and Staphylococcus xylosus. During fermentation of DFD meat, S. saprophyticus was less manifest than during that of normal meat. Enterobacterales mainly emerged in DFD meat during fermentation at low salt concentrations. The salt hurdle was insufficient to prevent Enterobacterales when acidification and initial pH were favourable for their growth.

  • Attribution of Listeria monocytogenes human infections to food and animal sources in Northern Italy
    Food Microbiol. (IF 4.089) Pub Date : 2020-01-20
    Virginia Filipello; Lapo Mughini-Gras; Silvia Gallina; Nicoletta Vitale; Alessandro Mannelli; Mirella Pontello; Lucia Decastelli; Marc W. Allard; Eric W. Brown; Sara Lomonaco

    Listeriosis is a foodborne illness characterized by a relatively low morbidity, but a large disease burden due to the severity of clinical manifestations and the high case fatality rate. Increased listeriosis notifications have been observed in Europe since the 2000s. However, the reasons for this increase are largely unknown, with the sources of sporadic human listerioris often remaining elusive. Here we inferred the relative contributions of several putative sources of Listeria monocytogenes strains from listerioris patients in Northern Italy (Piedmont and Lombardy regions), using two established source attribution models (i.e. ‘Dutch’ and ‘STRUCTURE’) in comparative fashion. We compared the Multi-Locus Sequence Typing and Multi-Virulence-Locus Sequence Typing profiles of strains collected from beef, dairy, fish, game, mixed foods, mixed meat, pork, and poultry. Overall, 634 L. monocytogenes isolates were collected from 2005 to 2016. In total, 40 clonal complexes and 51 virulence types were identified, with 36% of the isolates belonging to possible epidemic clones (i.e. genetically related strains from unrelated outbreaks). Source attribution analysis showed that 50% of human listerioris cases (95% Confidence Interval 44-55%) could be attributed to dairy products, followed by poultry and pork (15% each), and mixed foods (15%). Since the contamination of dairy, poultry and pork products are closely linked to primary production, expanding actions currently limited to ready-to-eat products to the reservoir level may help reducing the risk of cross-contamination at the consumer level.

  • Effect of endogenous CO2 overpressure on the yeast “stressome” during the “prise de mousse” of sparkling wine
    Food Microbiol. (IF 4.089) Pub Date : 2020-01-18
    Juan A. Porras-Agüera; Juan J. Román-Camacho; Jaime Moreno-García; Juan C. Mauricio; Juan Moreno; Teresa García-Martínez
  • Proteomic study of Enterococcus durans LAB18S growing on prebiotic oligosaccharides
    Food Microbiol. (IF 4.089) Pub Date : 2020-01-14
    Carolina Baldisserotto Comerlato; Ana Carolina Ritter; Kendi Nishino Miyamoto; Adriano Brandelli

    This study evaluates the influence of prebiotic carbohydrates, namely fructooligosaccharides (FOS) and galactooligosaccharides (GOS), on the protein expression of Enterococcus durans LAB18S. The strain was cultivated in 10 g L-1 FOS, GOS or glucose (control) and cellular proteins were extracted for mass spectrometry analysis. A total of 771 proteins were identified and 135 E. durans proteins were validated by the Scaffold algorithm. The proteins were functionally categorized according to Gene Ontology terms. Both FOS and GOS were used as carbon source by E. durans LAB18S, upregulating the production of proteins that may be associated with intestinal mucosa adhesion, carbohydrate and nitrogen metabolism, and stress response. Cells grown with GOS showed an increased expression of the cell division protein divIVA, EF-Tu and glyceraldehyde 3-phosphate dehydrogenase that have been associated with epithelial cell adhesion. The use of FOS stimulated the production of proteins related to amino acid metabolism and energy conversion, and ClpX protein, which plays an important role in protein turnover. The results of this study indicate that FOS and GOS can be metabolized by E. durans and stimulate the microorganism to produce proteins related to some desirable characteristics for a probiotic strain.

  • Phenotype and genomic background of Arcobacter butzleri strains and taxogenomic assessment of the species
    Food Microbiol. (IF 4.089) Pub Date : 2020-01-10
    Francesca Fanelli; Daniele Chieffi; Angela Di Pinto; Anna Mottola; Federico Baruzzi; Vincenzina Fusco

    In this study the phenotypic and genomic characterization of two Arcobacter butzleri (Ab) strains (Ab 34_O and Ab 39_O) isolated from pre-cut ready-to-eat vegetables was performed. Results provided useful data about their taxonomy and their overall virulence potential with particular reference to the antibiotic and heavy metal susceptibility. These features were moreover compared with those of two Ab strains isolated from shellfish and a genotaxonomic assessment of the Ab species was performed. The two Ab isolated from vegetables were confirmed to belong to the Aliarcobacter butzleri species by 16S rRNA gene sequence analysis, MLST and genomic analyses. The genome-based taxonomic assessment of the Ab species brought to the light the possibility to define different subspecies reflecting the source of isolation, even though further genomes from different sources should be available to support this hypothesis. The strains isolated from vegetables in the same geographic area shared the same distribution of COGs with a prevalence of the cluster “inorganic ion transport and metabolism”, consistent with the lithotrophic nature of Arcobacter spp.. None of the Ab strains (from shellfish and from vegetables) metabolized carbohydrates but utilized organic acids and amino acids as carbon sources. The metabolic fingerprinting of Ab resulted less discriminatory than the genome-based approach. The Ab strains isolated from vegetables and those isolated from shellfish endowed multiple resistance to several antibiotics and heavy metals.

  • Hepatitis E virus genotype 3 in echinoderms: first report of sea urchin (Paracentrotus lividus) contamination
    Food Microbiol. (IF 4.089) Pub Date : 2020-01-10
    Nânci Santos-Ferreira; João Rodrigo Mesquita; Enrique Rivadulla; Ângela S. Inácio; Paulo Martins da Costa; Jesus L. Romalde; Maria São José Nascimento

    Hepatitis E virus (HEV) deriving from manure application runoffs and faecal waste spill over of swine and human origin bypass wastewater treatment plants and contaminate coastal waters. Shellfish bioaccumulate enteric viruses such as HEV from fecally contaminated coastal waters and under current European Regulations, shellfish sanitary status surveillance is mandatory but only by means of bacterial faecal indicators. The sea urchins are under the same regulations and their vulnerability to fecal contamination has been pointed out. Since they are consumed raw and with no steps to control/reduce hazards, sea urchin contamination with enteric viruses can represent a food safety risk. Hence, the aim of the present study was to screen sea urchin gonads destined for human consumption for the presence of HEV. HEV was detected and quantified in gonads of sea urchins collected in north Portugal by reverse transcription-quantitative PCR (RT-qPCR) assay targeting the ORF3 region, followed by genotyping by a nested RT-PCR targeting the ORF2 region. Sequencing and phylogenetic analysis clustered the HEV sequence within genotype 3, subgenotype e. This the first study reporting HEV contamination of sea urchins. We hypothesize that like shellfish, sea urchins can also be a food vehicle for HEV transmission to humans.

  • Characterization of the microbial community composition in Italian Cinta Senese sausages dry-fermented with natural extracts as alternatives to sodium nitrite
    Food Microbiol. (IF 4.089) Pub Date : 2020-01-10
    Francesco Pini; Chiara Aquilani; Luciana Giovannetti; Carlo Viti; Carolina Pugliese

    Nitrite is widely used in meat products as a multifunctional additive, combining flavour and colour properties with antioxidant and antimicrobial effects. However, nitrite may form reaction products (i.e., nitrosamine) that are potentially carcinogenic to humans. The meat industry, in response to consumers’ demands for nitrite-free products, is seeking natural alternatives to nitrite, such as plant-based extracts. Three types of dry-fermented sausages were manufactured: NIT, containing 30 ppm of sodium nitrite; GSE, containing grape seed extract and olive pomace hydroxytyrosol; and CHE, containing chestnut extract and olive pomace hydroxytyrosol. Next-generation sequencing (NGS) was used to analyse microbial consortia, which were correlated with physical and chemical parameters. The prokaryotic community composition was similar among treatments, with a high relative abundance of Staphylococcus xylosus and Lactobacillus sakei, collectively accounting for 87% of the total community. However, significant differences were observed in both operational taxonomic unit (OTU) presence/absence and relative abundance. Ten genera (5 lactic acid bacteria) varied in abundance between treatments. The increase in Lactobacillaceae in CHE may explain the reduced pH levels detected in these samples. In conclusion, NGS analysis showed that the prokaryotic community composition was similar in GSE and NIT, while CHE varied in both the composition and relative abundance of different taxa.

  • Effect of slightly acidic electrolyzed water on natural Salmonella reduction and seed germination in the production of alfalfa sprouts
    Food Microbiol. (IF 4.089) Pub Date : 2020-01-09
    Chunling Zhang; Zhiyi Zhao; Gaoji Yang; Yiqi Shi; Yuyu Zhang; Xiaodong Xia; Chao Shi

    Microbial contamination of sprouts occurs easily because of the pathogens present on and in the seeds and the optimal conditions for bacteria growth provided during the germination and sprouting processes. This study examined the effect of using slightly acidic electrolyzed water (SAEW), a ‘generally recognized as safe’ (GRAS) disinfectant, in place of regular water in the production process of alfalfa sprouts. In the experiment, SAEW with various available chlorine concentrations (ACC, 25, 35, 45 mg/L) and different pH levels (5.0, 5.7 and 6.4) was used to soak seeds for different length of time (0.5 and 6 h), after which the variations in natural Salmonella, water absorption and seed germination (germination rate, weight and length of sprouts) were determined. The results showed that when the seeds were soaked with SAEW, albeit with different ACC (25, 35 and 45 mg/L) and pH levels (5.0, 5.7 and 6.4), a significant reduction of Salmonella and no negative effect on sprout quality was observed. The water absorption and germination rates were also not significantly adversely affected by SAEW soaking. These findings suggest that SAEW could be used to decontaminate natural Salmonella in the production of alfalfa sprouts, with no negative side effects on the alfalfa seeds.

  • Evaluation of a Hybrid In-field Sampling Method for the Detection of Pathogenic Bacteria through Consideration of a priori Knowledge of Factors Related to Non-random Contamination
    Food Microbiol. (IF 4.089) Pub Date : 2020-01-08
    Aixia Xu; Robert L. Buchanan

    Pre-harvest testing is increasingly used to enhance the microbial safety of fresh produce. Traditional sampling assumes that sample collectors have no information on potential contamination sources. Knowledge of such factors could potentially increase the effectiveness of pre-harvest sampling programs. Simulation modeling and field validation trials were used to evaluate a hybrid “Samples of Opportunity” (SOO) sampling method that included a portion of the samples based on the sampler’s knowledge of risk factors in pre-harvest produce fields. Relative effectiveness of SOO sampling was compared with three traditional sampling methods. These evaluations were based on three non-random contamination scenarios. The mean detection probability of SOO is 96% higher than traditional sampling methods (p<0.001). However, if the site of actual contamination is offset from assumed area of contamination, the detection probability of SOO sampling drops, and becomes similar or even worse than that achieved by the other sampling methods. Preliminary field validation trials indicated indeed that SOO performed better than the other three sampling methods. This study provides a mathematical approach for evaluating the effectiveness of four pre-harvest sampling methods, and suggests that having a priori knowledge of the contamination source in the field would improve effectiveness of sampling, particularly if done using a standardized protocol.

  • Diversity of the metabolic profiles of a broad range of lactic acid bacteria in soy juice fermentation
    Food Microbiol. (IF 4.089) Pub Date : 2020-01-08
    Olivier Harlé; Hélène Falentin; Jérôme Niay; Florence Valence; Céline Courselaud; Victoria Chuat; Marie-Bernadette Maillard; Éric Guédon; Stéphanie-Marie Deutsch; Anne Thierry

    This study explores the ability of lactic acid bacteria (LAB) to ferment soy juice. The ability of 276 LAB strains from 25 species to ferment the principal soy carbohydrates, sucrose, raffinose or stachyose was tested in synthetic media and a soy juice. Fermented soy juices (FSJs) were characterized for their odor. Selected FSJs were characterized by targeted metabolomics. All Streptococcus, 83% of Leuconostoc and Lactobacillus and 41% of Lactococcus strains were sucrose-positive, while only 36% of all the LAB strains tested were raffinose-positive and 6% stachyose-positive. Nearly all (97%) the sucrose-positive strains fermented soy juice, indicating that an ability to use sucrose is a good criterion to select strains for soy juice fermentation. Among the most efficient acidifying strains, 46 FSJs had an odor deemed to be acceptable. FSJ composition was dependent on both species and strains: 17/46 strains deglycosylated soy juice isoflavones, the 27 S. thermophilus strains converted a mean 4.4 ± 0.1 g/L of sucrose into 3.0 ± 0.1 g/L of lactic acid versus 5.2 ± 0.1 g/L into 2.2 ± 0.1 g/L for the 18 Lactobacillus and one Lactococcus strains. This study highlights the diversity of the metabolic profiles of LAB strains in soy juice fermentation.

  • Effect of Combination of Oxyrase and Sodium Thioglycolate on Growth of Clostridium perfringens from Spores under Aerobic Incubation
    Food Microbiol. (IF 4.089) Pub Date : 2020-01-07
    Zhen Jia; Yanhong Liu; Chang-An Hwang; Lihan Huang

    Clostridium perfringens is a strictly anaerobic pathogen that requires absence of oxygen for its growth in laboratory experiments, which is usually attained by using an anaerobic chamber or anaerobic jars. However, it has been demonstrated that C. perfringens may survive for short periods of times due to its adaptive response to O2. Therefore, the objective of this study was to explore the application of Oxyrase (OX) and sodium thioglycolate (ST) as oxygen scavengers, used alone or in combination, for observation of the growth of C. perfringens under aerobic incubation. The growth of C. perfringens from spores in Schaedler Anaerobe Agar containing different levels and combinations of OX and ST was observed at temperatures between 20 and 50°C under aerobic incubation. The kinetic parameters, including lag time, specific growth rate, and maximum cell concentrations in the stationary phase, were determined. The results indicated that ST at concentrations of 0.025 and 0.05% (w/w), although allowing eventual growth of C. perfringens, prolonged its lag times, while OX at 1.5% only allowed for a lower growth rate. OX at 3% enhanced the growth of C. perfringens at temperatures between 30 and 50°C, while higher levels of OX were needed in the medium to support the growth of C. perfringens during storage at 25°C (>6% OX) and 20°C (>9% OX), due to the effect of temperature on enzyme activity. No significant difference was found in the kinetic parameters of C. perfringens incubated aerobically with OX and the control (without OX or ST) in an anaerobic chamber. Therefore, OX at appropriate concentrations may allow the observation of the growth of C. perfringens under aerobic incubation conditions without the need of an anaerobic device.

  • Honokiol suppresses mycelial growth and reduces virulence of Botrytis cinerea by inducing autophagic activities and apoptosis
    Food Microbiol. (IF 4.089) Pub Date : 2019-12-30
    Danying Ma; Xiaomin Cui; Zhanquan Zhang; Boqiang Li; Yong Xu; Shiping Tian; Tong Chen

    Fungal pathogens lead to severe quality deterioration and yield loss, making it urgent to explore efficient measures to control fungal diseases at the preharvest and postharvest stages of plants. Therefore, studies on natural substances targeting alternative antimicrobial targets have become hot spots of research. Here, we show that honokiol, a polyphenolic compound obtained from Magnolia officinalis, significantly suppressed mycelial growth and reduced virulence of B. cinerea on harvested fruit by inducing autophagic activities and apoptosis. Moreover, honokiol was capable of abolishing the mitochondrial membrane potential and inducing the accumulation of reactive oxygen species. Some key genes involved in pathogenicity on fruit were also found significantly down-regulated. In summary, honokiol was effective as an alternative agent targeting autophagic and apoptotic machineries to control the incidence of gray mold, which may further enrich the toolkit of crop managers for fighting postharvest diseases caused by this and similar fungi.

  • Large genetic diversity of Arcobacter butzleri isolated from raw milk in Southern Italy
    Food Microbiol. (IF 4.089) Pub Date : 2019-12-28
    Caruso Marta; Normanno Giovanni; Miccolupo Angela; Capozzi Loredana; Bonerba Elisabetta; Difato Laura; Mottola Anna; Di Pinto Angela; Santagada Gianfranco; Parisi Antonio

    Arcobacter butzleri is a zoonotic foodborne pathogen able to cause enteric and extraintestinal diseases. Its occurrence in foodstuff is well recognized worldwide but data on its presence in foods from Southern Italy are scarce. In this study the results on the occurrence and genotyping of Arcobacter spp. in bulk milk samples collected in Southern Italy are reported. Out of 484 samples, 64 (13.2%) resulted positive for the presence of Arcobacter spp. using Real Time PCR but as few as 31.2% of these samples turned out as positive by using the cultural method, showing an overall prevalence of 4.1%. All isolates were identified as A. cryaerophilus using the biochemical identification whilst the sequencing of the atpA gene revealed that all the isolates were A. butzleri. Among the confirmed isolates, 16 different Sequence Types (ST) were identified using the Multi Locus Sequence Typing (MLST), 14 (87.5 %) of which were previously unreported. Our survey reveals the presence of A. butzleri in bulk tank milk from Southern Italy and highlights the discrepancy between the two approaches used both for the detection (i.e., real time PCR vs cultural method) and the identification (i.e., biochemical test vs aptA sequencing) of Arcobacter spp In addition, a large genetic diversity among the isolates was detected and this makes the identification of source of the infections very challenging in outbreaks investigation.

  • The metagenome-assembled genome of Candidatus Oenococcus aquikefiri from water kefir represents the species Oenococcus sicerae
    Food Microbiol. (IF 4.089) Pub Date : 2019-12-27
    Marko Verce; Luc De Vuyst; Stefan Weckx

    Recently, a metagenomic study of a water kefir fermentation ecosystem enabled the reconstruction of a metagenome-assembled genome (MAG) of an Oenococcus species that was different from the three species of this genus known so far. Therefore, the name Candidatus Oenococcus aquikefiri was proposed for this novel Oenococcus species. In the meantime, however, a fourth member of the genus, Oenococcus sicerae, isolated from French cider, was reported. The comparison of its genome sequence with the Candidatus O. aquikefiri MAG showed an average nucleotide identity (ANI) value of 98.53 %. In addition, the 16S rRNA and pheS genes of the two species were 99.4 % and 99.9 % identical, respectively. As the presence of O. sicerae in a water kefir metagenome was also revealed by metagenomic recruitment plotting, it can be stated that Candidatus O. aquikefiri and O. sicerae belong to the same species. Intraspecies variations include the presence or absence of a citrate lyase operon and components of various phosphotransferase (PTS) transport systems.

  • Critical points affecting the microbiological safety of bell peppers washed with peroxyacetic acid in a commercial packinghouse
    Food Microbiol. (IF 4.089) Pub Date : 2019-12-24
    Francisco López-Gálvez; Pilar Truchado; Juan A. Tudela; Maria I. Gil; Ana Allende

    The washing stage from a bell pepper commercial packinghouse was assessed to study some of the critical control points related to bacterial cross-contamination. The washing line comprised two overhead spray bars applications: a pre-wash step without peroxyacetic acid (PAA), and a wash step with PAA. The physicochemical characteristics of the wash water and the bacterial quality and safety of the wash water and bell peppers (including aerobic mesophilic bacteria (AMB), Salmonella spp., and Shiga-toxigenic E. coli (STEC)) were studied. Additionally, the performance of commercial test methods (reflectometry, amperometric probe, chronoamperometric sensor) for measuring the residual concentration of PAA was examined. The bacterial load of the pre-wash water (8.7±1.3 log cfu/100 mL AMB) was very high and thus peppers after the pre-wash showed a significantly higher bacterial load (4.9±0.9 log cfu/g AMB) than the unwashed (3.8±0.7 log cfu/g AMB) or the washed peppers (3.3±0.8 log cfu/g AMB) (p<0.05). However, no pathogenic bacteria were detected in bell pepper samples (n=40), and only one water sample was confirmed positive for STEC (n=64, 1.6% prevalence). The chronoamperometric sensor (PAAsense) and the online amperometric probe showed similar results, while the reflectometry (Quantofix) significantly sub estimated (p<0.05) PAA concentration. The results obtained highlight the need for interventions to improve hygiene in the washing line to ensure the microbiological quality and safety of bell peppers. The maintenance of optimal PAA concentrations in all the washing steps is critical for reducing the chance of water-mediated cross-contamination.

  • Exploring core functional microbiota related with flavor compounds involved in the fermentation of a natural fermented plain sufu (Chinese fermented soybean curd)
    Food Microbiol. (IF 4.089) Pub Date : 2019-12-24
    Wenmeng He; Hau Yin Chung

    This study aimed to explore the core functional microbiotas related to flavor compounds involving in a naturally fermented soybean curd (plain sufu). Properties such as physicochemical parameters, flavor compounds (17 free amino acids, 21 fatty acids, and 14 aroma volatiles) and microbiota profiles were investigated, and their correlations were explored at 8 stages during production. Results from principal component analysis, multiple factor analysis, and partial least squares-discrimination analysis showed that these properties varied significantly in the eight stages. Furthermore, based on Pearson correlation coefficients and Variable importance for predictive components values between the microbiota profiles and flavor compounds, nine bacterial (Bacillus, Enterobacter, Lactobacillus, Sphingobacterium, Stenotrophomonas, Tetragenococcus, Trabulsiella, Unclassified, and Weissella) and six fungal (Alternaria, Sterigmatomyces, Actinomucor, Fusarium, Debaryomyces, Candida) genera were identified as core functional microbiotas significantly affecting the production of flavor compounds during the natural production. Overall, this study provided a comprehensive description of the dynamic changes of physicochemical parameters, flavor compounds, and microbiota profiles throughout the natural production of plain sufu. The similarities and variations among different stages, as well as correlation between flavor compounds and microbiotas would help to understand the mechanism of plain sufu production, and further to enhance the quality control of plain sufu.

  • Modelling and validation of the antifungal activity of DL-3-phenyllactic acid and acetic acid on bread spoilage moulds
    Food Microbiol. (IF 4.089) Pub Date : 2019-12-19
    Els Debonne; An Vermeulen; Naomi Bouboutiefski; Tony Ruyssen; Filip Van Bockstaele; Mia Eeckhout; Frank Devlieghere

    Most interesting antifungal compounds from sourdough fermentation are acetic acid (AA) and DL-3-phenyllactic acid (PLA). Although the role of pH on the activity of organic acids has been established long time ago, no information is available on the importance of undissociated acid (HA) expressed on the aqueous phase of bread (CHA, mmole/L). Mostly, concentrations (mmole/kg dough or bread, CTOT) and pH are given side by side. The aim of this study was to show the importance of CHA for adequate comparison of in-vitro growth data with bread shelf-life. Growth of Penicillium paneum and Aspergillus niger was recorded using a micro-dilution assay with optical density measurements. Parameters such as aw (0.94-0.98), pH (4.6-6.0), temperature (10-30°C), time (0-8 days) and CTOT (0-300 mM) were varied. Growth/no-growth models were developed and shelf-life tests of par-baked breads of 45 days at 20°C were conducted. The modelled inhibitory concentrations of undissociated acid were comparable with the shelf-life test of bread: (PLA) 50 versus 39-84 mmole/L; (AA) 110 versus 110-169 mmole/L. This study showed the applicability of G/NG models for bread shelf-life prediction and highlighted the importance of CHA. Moreover, it was found that naturally present PLA in sourdough bread is insufficient to increase bread shelf-life.

  • Effect of storage temperature, water activity, oxygen headspace concentration and pasteurization intensity on the time to growth of Aspergillus fischerianus (teleomorph Neosartorya fischeri)
    Food Microbiol. (IF 4.089) Pub Date : 2019-12-19
    Juliana Lane Paixão dos Santos; Simbarashe Samapundo; Stefani Djunaidi; An Vermeulen; Anderson S. Sant’Ana; Jan Van Impe; Frank Devlieghere

    This study aims to assess, by means of a full factorial design, the effect of storage temperature (10-30°C), water activity (aw, 0.87-0.89), headspace oxygen (O2) level (0.15-0.80%) and pasteurization intensity (95°C, 100°C or 105°C/15sec) on the time to visible growth (tv, days) of Aspergillus fischerianus on acidified Potato Dextrose Agar (aPDA, pH 3.6) for up to 90 days. Moreover, in order to validate the results obtained on aPDA, 12 conditions were selected and assessed in concentrate strawberry-puree based medium. Overall, storage temperature had the greatest effect on the tv of A. fischerianus on the evaluated conditions. At 10°C, no visible growth was observed over the 90 day incubation period, whilst visible mycelia (diameter ≥ 2mm) were present in 37% and 89% of the conditions at 22°C and 30°C, respectively. Pasteurization intensity had only a minor effect on the outgrowth of A. fischerianus. Growth inhibition was observed when aw was reduced to 0.870 ± 0.005 in combination with very low headspace O2 levels (0.15% ± 0.10) in both, aPDA and concentrate strawberry-based media, regardless of the incubation temperature and heat pasteurization intensity. Overall, longer tv’s were required when incubation was done at 22°C compared to 30°C. Ultimately, the effect of O2 (0.05 and 1%) and pasteurization intensity (95°C and 105°C/15sec) were evaluated on totally 22 fruit purees (un-concentrates and concentrates) over a 60 day storage period. None of the concentrates purees (aw ≤0.860) evaluated in this study supported the growth of A. fischerianus. On the other hand, A. fischerianus growth inhibition was only observed when the O2 levels were ≤ 0.05% on un-concentrates fruit purees (aw ≥ 0.980) stored at ambient temperature (22°C). Combination of multiple stress factors effectively inhibited growth of A. fischerianus. In general, storage of fruit purees at low temperatures (<10°C) or distribution in the form of concentrates can be considered as important strategies to prevent the growth of spoilage associated heat-resistant moulds.

  • Superchilling in combination with modified atmosphere packaging resulted in long shelf-life and limited microbial growth in Atlantic cod (Gadus morhua L.) from capture-based-aquaculture in Greenland
    Food Microbiol. (IF 4.089) Pub Date : 2019-12-18
    Jonas Steenholdt Sørensen; Niels Bøknæs; Ole Mejlholm; Paw Dalgaard

    Sensory, chemical and microbial changes for Atlantic cod (Gadus morhua L.) filets from capture-based-aquaculture in Greenland were studied. The objective was to determine shelf-life and indices of spoilage for iced or superchilled fillets when stored in air, or modified atmosphere packed (MAP; 40% CO2 and 60% N2). MAP iced storage extended the sensory shelf-life from 15 days to 21 days compared to storage in air. With superchilling at -1.7 ○C sensory shelf-life was above 32 days, and no formation of total volatile nitrogen (TVN) was observed irrespective of storage in air or MAP. pH of ≥7.0, TVN (≥35 mg-N/100g) and trimethylamine (≥20 mg-N TMA/100g) were promising indices of spoilage. Aerobic viable counts were less valuable indices of spoilage as the dominating microbiota of cod in air (Pseudomonas spp., Photobacterium spp., Shewanella spp., Acinetobacter spp.) changed to Photobacterium spp. in MAP cod. Spoilage activity determined as the yield factor for TVN formation was 6-200 folds higher for Photobacterium spp. compared to Shewanella spp. and Pseudomonas spp. Photobacterium carnosum was responsible for TVN formation in iced cod irrespective of storage in air or MAP, and it was identified at the specific spoilage organism that limited iced product shelf-life.

  • Pichia kudriavzevii retards fungal decay by influencing the fungal community succession during cherry tomato fruit storage
    Food Microbiol. (IF 4.089) Pub Date : 2019-12-16
    Xia Liu; Yu Gao; Hongyuan Yang; Limei Li; Yishan Jiang; Yuan Li; Jiaxuan Zheng

    In this study, P. kudriavzevii was isolated and identified as an effective antagonistic yeast, which could significantly inhibit the rotting rate, weight loss, and delay the color change, with no effect on total soluble solids (TSS), titratable acid (TA), or firmness during cherry tomato storage. High-throughput sequencing was used to survey the effect of P. kudriavzevii on fungal community throughout cold storage. The results showed that the biological succession of predominant pathogens was disrupted by P. kudriavzevii. The abundance of Botrytis and Alternaria was higher in the control than upon P. kudriavzevii treatment at 28 d, but some yeast genera such as Naganishia, Wickerhamomyces, and Cutaneotrichosporon at 14 d, Pichia and Sporidiobolus at 21 d, and Cystofilobasidium at 28 d, had relatively higher abundances in P. kudriavzevii treatments than the control. Oddly, as an antagonist agent, P. kudriavzevii was not the dominant population, indicating that altering the course of succession of the fungal community may be an effective mechanism of antagonistic yeast. Furthermore, the total network correlation analysis of fungal community revealed that the community development was more dependent on similarities in function than on taxonomic relationships.

  • Decontamination of dried whole black peppercorns using ultraviolet-c irradiation
    Food Microbiol. (IF 4.089) Pub Date : 2019-12-13
    Alonzo A. Gabriel; Mikaella Marie C. David; Maxine Sebastianne C. Elpa; Juan Carlos D. Michelena

    This study determined the efficacy of UV-C as a decontamination process against some foodborne bacteria in dried whole black peppercorns. Artificially-inoculated Salmonella enterica, Escherichia coli O157:H7, Listeria monocytogenes, Pseudomonas aeruginosa, and Staphylococcus aureus were subjected to UV-C with a surface irradiance of 0.43 mW/cm2 and were all found to exhibit a biphasic inactivation pattern with fast log-linear inactivation followed by a tail. Total log reductions (TLR) ranged from 1.92 (S. aureus) to 3.60 log CFU/g (E. coli O157:H7). Increasing the lamp number from 1 to 5 also linearly (R2 =0.98) increased the surface irradiance from 0.43 to 1.70 and the TLR of the most resistant S. aureus from 1.92 to 2.62 log CFU/g. Quality evaluation showed very small, variable changes in color coordinates, which were not detected by a same/different test involving a 50-member sensory evaluation panel. Mercury deposition was not detected after a maximum exposure time of 90 min to 0.43 and 1.70 mW/cm2. Finally small, non-significant changes in the innate bacterial microflora of the black peppercorns were determined after 90 min-treatment using 1 lamp and 5 lamps, emphasizing the limitation of utility of UV-C as additional decontamination process for post-process-introduced microorganisms. Good Manufacturing Practices throughout the dried black peppercorn manufacturing process were recommended.

  • Metabolic characterization of eight Escherichia coli strains and acidic responses of selected strains revealed by NMR spectroscopy
    Food Microbiol. (IF 4.089) Pub Date : 2019-12-11
    Lin Chen, Xue Zhao, Ji'en Wu, Qin Liu, Xinyi Pang, Hongshun Yang

    The metabolic diversity of Escherichia coli strains (non-pathogenic E. coli ATCC 25922, and pathogenic E. coli O157:H7, O26:H11, O45:H2, O103:H11, O111, O121:H19, and O145) was tested using nuclear magnetic resonance. Based on two representative two-dimensional 1H-13C spectra, 38 metabolites were identified in E. coli intracellular samples. Principal component analysis indicated that metabolites including lysine, arginine, α-ketoglutaric acid, adenosine, and fumaric acid were responsible for the separation of E. coli ATCC 25922. Relatively large metabolic differences between ATCC 25922 and the pathogenic strains were recoded. The most varied pairwise group (ATCC 25922 vs. O26:H11) was further analysed. The screened metabolites and enrichment pathway tests revealed different amino acid metabolism and higher requirement for energy production in the pathogenic strains. The acidic responses of the selected strains were further tested. The in vitro and in vivo inactivation kinetics, morphological changes, and protein leakage showed higher acid tolerance of E. coli O26:H11. Metabolic analysis of the two strains under acidic stress revealed alternative metabolites and pathways in the two groups. Pathogenic O26:H11 was characterised by higher energy production and amino acid metabolism (lysine and glutamic acid). Real-time PCR tests confirmed that glutamic acid dependent decarboxylase/antiporter system was the major acid resistance mechanism.

  • Characterization of Escherichia coli possessing the locus of heat resistance isolated from human cases of acute gastroenteritis
    Food Microbiol. (IF 4.089) Pub Date : 2019-12-11
    Angela Ma, Heather Glassman, Linda Chui

    The purpose of this study was to identify Escherichia coli isolates obtained from patients experiencing acute gastroenteritis that possess the locus of heat resistance (LHR) and characterize their heat resistance upon exposure to temperatures of 60°C and 71°C. From a collection of 613 clinical E. coli strains, 3 heat resistant E. coli isolates were identified. Two of the 3 isolates were stx1 positive; no isolates possessed stx2 as determined by qPCR. D60-values of heat resistant isolates all exceeded 10.20 min with one isolate’s D60-values ranging from 20.46 to 72.47 min. The presence of 4% additional NaCl significantly increased D60-values of 2 clinical isolates. Cell reductions of heat resistant isolates in ground beef patties grilled to 60°C and 71°C remained above 2.8 and 4.9 log CFU/mL, respectively, compared to reductions of 6.1 log CFU/mL and greater in heat sensitive E. coli. Constitutive expression of novel Clp protease ClpK, encoded on open reading frame 3 of the LHR, was identified in all heat resistant isolates by SDS-PAGE and peptide mass fingerprinting. This data is the first to report heat resistant E. coli possessing the LHR involved in clinical infection, highlighting the potential threat of heat resistant enteric pathogens on food safety.

  • Melatonin and glycolytic protein interactions are related to yeast fermentative capacity
    Food Microbiol. (IF 4.089) Pub Date : 2019-12-06
    María Ángeles Morcillo-Parra, Beatriz González, Gemma Beltran, Albert Mas, María-Jesús Torija

    Melatonin is an indole amine that interacts with some proteins in mammals, such as calreticulin, calmodulin or sirtuins. In yeast, melatonin is synthetized and interacts with glycolytic proteins during alcoholic fermentation in Saccharomyces cerevisiae. Due to its importance as an antioxidant molecule in both Saccharomyces and non-Saccharomyces yeasts, the aim of this study was to determine the intracellular and extracellular synthesis profiles of melatonin in four non-Saccharomyces strains (Torulaspora delbrueckii, Hanseniaspora uvarum, Starmeralla bacillaris and Metschnikowia pulcherrima) and to confirm whether glycolytic enzymes can also interact with this molecule in non-conventional yeast cells. Melatonin from fermentation samples was analyzed by liquid chromatography mass spectrometry, and proteins bound to melatonin were immunopurified by melatonin-IgG-Dynabeads. Melatonin was produced in a similar pattern in all non-Saccharomyces yeast, with M. pulcherrima and S. bacillaris being the highest producers. However, melatonin only bound to proteins in two non-conventional yeasts, S. bacillaris and T. delbrueckii, which specifically had higher fermentative capacities. Sequence analysis showed that most proteins shared high levels of homology with glycolytic enzymes, but an RNA-binding protein, the elongation alpha factor, which is related to mitochondria, was also identified. This study reports for the first time the interaction of melatonin with proteins inside non-Saccharomyces yeast cells. These results reinforce the possible role of melatonin as a signal molecule, likely related to fermentation metabolism and provide a new perspective for understanding its role in yeast.

  • Evaluation of the U.S. Food and Drug Administration validated molecular method for detection of Cyclospora cayetanensis oocysts on fresh and frozen berries
    Food Microbiol. (IF 4.089) Pub Date : 2019-12-04
    Angela Assurian, Helen Murphy, Laura Ewing, Hediye Nese Cinar, Alexandre da Silva, Sonia Almeria

    Outbreaks and sporadic cases of Cyclospora cayetanensis have been linked to consumption of berries. The efficacy of the U.S. Food and Drug Administration (FDA) method for detection of C. cayetanensis was evaluated in fresh berries (blackberries, strawberries, blueberries and mixed berries) and in frozen mixed berries. The protocol included seeding with C. cayetanensis oocysts, produce washing, DNA extraction and a dual TaqMan assay. As few as five oocysts were detected in every type of fresh berry analyzed. All berry samples seeded with 200 oocysts were positive and all unseeded berry samples were negative. No significant differences were observed among any of the berry types analyzed in detection rates, CT values and estimated oocyst recovery percentages. Mixed berries were seeded and frozen for up to seven weeks. As few as five oocysts were also detected. No significant differences were observed in C. cayetanensis CT values between fresh and frozen mixed berries at any seeding level. In conclusion, the FDA BAM Chapter 19B method for the detection of Cyclospora was robust, consistent, and showed high sensitivity in all types of berries analyzed. Evaluation of the FDA detection method in berries will provide reliable laboratory support for surveillance programs and for outbreak investigations.

  • Glove-mediated transfer of Listeria monocytogenes on fresh-cut cantaloupe
    Food Microbiol. (IF 4.089) Pub Date : 2019-12-03
    Yan Qi, Yingshu He, Larry R. Beuchat, Wei Zhang, Xiangyu Deng

    The common use of gloves in retail practices represents a potential route for cross contamination of foodborne pathogens in fresh-cut produce. Using fresh-cut cantaloupe as a food model, we investigated factors that may influence glove-mediated cross contamination by Listeria monocytogenes and developed mathematical models to illustrate the patterns of transfer during fresh-cutting practices. Contact time (2, 5, 10 s), contact pressure (0.05, 0.18, 0.37 psi), and glove type (nitrile, polyvinyl chloride, polyethylene) did not have a significant effect on transfer of L. monocytogenes from cantaloupe rind to flesh, or from flesh to flesh. However, glove type appeared to affect L. monocytogenes transfer from the stem scar tissue to cantaloupe flesh (P = 0.0371). Transfer from rind pieces that had been washed with water was significantly higher than transfer from pieces that had not been washed (P = 0.0006). Predictive modeling and experimental validation suggested that transfer of L. monocytogenes on cantaloupe flesh persists over 85 pieces through consecutive contacts with a gloved hand. Findings of the study provide new scientific data to aid researchers, retailers, and caterers in safety risk assessments of fresh-cut practices used to prepare cantaloupes and other produce items.

  • Effect of temperature on the growth of Staphylococcus aureus in ready-to-eat cooked rice with pork floss
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-28
    Kuan-Hung Lu, Yi-Jyun Sheen, Tsui-Ping Huang, Shu-Hui Kao, Chun-Lung Cheng, Cheng-An Hwang, Shiowshuh Sheen, Lihan Huang, Lee-Yan Sheen

    Cooked rice with pork floss (CRPF) wrapped in dried seaweed is one of the most popular ready-to-eat (RTE) foods in many Asian countries, particularly in Taiwan. The products are susceptible to Staphylococcus aureus contamination and temperature abuse during manufacturing, distribution, and storage. The objective of this study was to examine the effect of temperature on its growth in RTE CRPF for use in risk assessment and prevention of staphylococcal food poisoning (SFP). Inoculated CRPF samples were stored at 4, 12, 18, 25, and 35°C, and the change in the populations of S. aureus during storage were analyzed using three primary models to determine specific growth rate (μmax), lag-phase duration (λ), and maximum population density (ymax). The Ratkowsky square-root and Huang square-root (HSR) models were used as the secondary models to describe the effect of temperature on μmax, and a linear and an exponential regression models were used to describe the effect of temperature on λ and ymax, respectively. The model performance was evaluated by the root mean square error (RMSE), bias factor (Bf), and accuracy factor (Af) when appropriate. Results showed that three primary models were suitable for describing the growth curves, with RMSE ≤ 0.7 (log MPN/g). Using μmax obtained from the Huang model, the minimum growth temperature (Tmin) estimated by the HSR model was 7.0 °C, well in agreement with the reported Tmin. The combination of primary and secondary models for predicting S. aureus growth was validated by additional growth curves at 30°C, which showed that the RMSE was 0.6 (log MPN/g). Therefore, the developed models were acceptable for predicting the growth of S. aureus in CRPF under likely temperature abuse conditions and can be applied to assess the risk of S. aureus in CRPF and design temperature controls to reduce the risk of SFP.

  • Global Transcriptomic Analysis of Lactobacillus plantarum CAUH2 in Response to Hydrogen Peroxide Stress
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-27
    Zhengyuan Zhai, Yang Yang, Hui Wang, Guohong Wang, Fazheng Ren, Zaigui Li, Yanling Hao

    To overcome the deleterious effects of hydrogen peroxide, Lactobacillus plantarum elicits an adaptive response to oxidative stress. In this study, global transcriptomic analysis revealed that L. plantarum CAUH2 expanded its carbon source utilizing profile and enhanced glycolysis to produce more ATP to confront with H2O2 stress. Some antioxidant enzymes including NADH peroxidase, thioredoxin reductase and glutathione peroxidase were 6.11, 36.76 and 6.23-fold up-regulated at transcription level for H2O2 scavenging. Meanwhile, free ferrous iron (Fe2+) was maintained at low concentrations in the cytoplasm, which could limit Fenton reaction and reduce the production of hydroxyl radicals. To repair DNA lesion caused by H2O2, both base excision repair system and recombinational DNA repair pathway were employed by L. plantarum CAUH2. In addition, the expression of methionine sulfoxide reductases and thioredoxin were up-regulated to repair oxidized proteins. It is noteworthy that some transcriptional regulators (Spx, CcpA and MarR1) were predicted to participate in the adaptive response to H2O2 stress, suggesting that L. plantarum CAUH2 utilized a wide array of sensors to monitor oxidative stress and modulated the transcriptional regulation network under H2O2 stress. These findings provide novel insight into the protective mechanisms developed by L. plantarum to cope with oxidative stress.

  • Combination of mild heat and plant essential oil constituents to inactivate resistant variants of Escherichia coli in buffer and in coconut water
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-26
    Elisa Gayán, Elise Geens, Daniel Berdejo, Diego García-Gonzalo, Rafael Pagán, Abram Aertsen, Chris W. Michiels

    The growing demand for minimally processed foods with clean labels has stimulated research into mild processing methods and natural antimicrobials to replace intensive heating and conventional preservatives, respectively. However, we have previously demonstrated that repetitive exposure of some bacteria to mild heat or subinhibitory concentrations of essential oil constituents (EOCs) may induce the emergence of mutants with increased resistance to these treatments. Since the combination of mild heat with some EOCs has a synergistic effect on microbial inactivation, we evaluated the potential of such combinations against our resistant E. coli mutants. While citral, carvacrol and t-cinnamaldehyde synergistically increased heat inactivation (53.0ºC, 10 min) of the wild-type MG1655 suspended in buffer, only the combination with carvacrol (200 μl/l) was able to mitigate the increased resistance of all the mutants. Moreover, the combination of heat and carvacrol acted synergistically inactivating heat-resistant variants of E. coli O157:H7 (ATCC 43888). This combined treatment could synergistically achieve more than 5 log10 reductions of the most resistant mutants in coconut water, although the temperature had to be raised to 57.0°C. Therefore, the combination of mild heat with carvacrol appears to hold promise for mild processing, and it is expected to counteract the development of heat resistance.

  • Investigation of genomic characteristics and carbohydrates’ metabolic activity of Lactococcus lactis subsp. lactis during ripening of a Swiss-type cheese
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-26
    Marios Mataragas

    Genetic diversity and metabolic properties of Lactococcus lactis subsp. lactis were explored using phylogenetic, pan-genomic and metatranscriptomic analysis. The genomes, used in the current study, were available and downloaded from the GenBank which were primarily related with microorganisms isolated from dairy products and secondarily from other foodstuffs. To study the genetic diversity of the microorganism, various bioinformatics tools were employed such as average nucleotide identity, digital DNA-DNA hybridization, phylogenetic analysis, clusters of orthologous groups analysis, KEGG orthology analysis and pan-genomic analysis. The results showed that Lc. lactis subsp. lactis strains cannot be sufficiently separated into phylogenetic lineages based on the 16S rRNA gene sequences and core genome-based phylogenetic analysis was more appropriate. Pan-genomic analysis of the strains indicated that the core, accessory and unique genome comprised of 1036, 3146 and 1296 genes, respectively. Considering the results of pan-genomic and KEGG orthology analyses, the metabolic network of Lc. lactis subsp. lactis was rebuild regarding its carbohydrates’ metabolic capabilities. Based on the metatranscriptomic data during the ripening of the Swiss-type Maasdam cheese at 20oC and 5oC, it was shown that the microorganism performed mixed acid fermentation producing lactate, formate, acetate, ethanol and 2,3-butanediol. Mixed acid fermentation was more pronounced at higher ripening temperatures. At lower ripening temperatures, the genes involved in mixed acid fermentation were repressed while lactate production remained unaffected resembling to a homolactic fermentation. Comparative genomics and metatranscriptomic analysis are powerful tools to gain knowledge on the genomic diversity of the lactic acid bacteria used as starter cultures as well as on the metabolic activities occurring in fermented dairy products.

  • Aureobasidium pullulans volatile organic compounds as alternative postharvest method to control brown rot of stone fruits
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-25
    Alessandra Di Francesco, Michele Di Foggia, Elena Baraldi

    Volatile compounds produced by L1 and L8 strains were assayed against mycelia and conidia growth of Monilinia laxa, M. fructicola, M. polystroma, and M. fructigena of stone fruits. Results showed that volatile metabolites inhibited significantly pathogens growth, in particular M. fructigena mycelium growth (70% by L1 and 50% by L8) and M. fructicola conidia germination (85% by L1 and 70% by L8) compared to the control. Moreover, the antagonistic activity was enhanced by the addition of asparagine (120 mg L-1) in the culture media composition. Synthetic pure compounds were tested in vitro on pathogens mycelial and conidia growth and their EC50 values were estimated, confirming 2-phenethyl as the most active compound. For this reason 2-phenethyl and VOCs of both yeast strains were assayed in vivo on cherry, peach, and apricot fruits. Regarding peach fruit, both treatments, yeasts and pure compounds, displayed the best inhibiting action against all the pathogens especially against M. laxa (100% by L1, 84% by L8 and 2-phenethyl). ATR/IR spectroscopy analysis showed how VOCs produced by both strains increase the fruit waxes complexity reducing the pathogens attack so playing an essential role in the antagonistic activity of both yeast strains and on fruit structural composition.

  • A multiplex oligonucleotide ligation-PCR method for the genoserotyping of common Salmonella using a liquid bead suspension assay
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-25
    Mathieu Gand, Wesley Mattheus, Nancy H.C. Roosens, Katelijne Dierick, Kathleen Marchal, Sigrid C.J. De Keersmaecker, Sophie Bertrand

    Salmonella is a major pathogen having a public health and economic impact in both humans and animals. Six serotypes of the Salmonella genus are mentioned in the Belgian and European regulation as to be rapidly excluded from the food chain (EU regulation N°2160/2003, Belgian royal decree 27/04/2017). The reference method for Salmonella serotyping, including slide-agglutination and biochemical tests, is time-consuming, expensive, not always objective, and therefore does not match the fast identification criteria required by the legislation. In this study, a molecular method, using genetic markers detected by Multiplex Oligonucleotide Ligation – PCR and Luminex technology, was developed for the identification of the 6 Salmonella serotypes and their variants subjected to an official control. The resulting method was validated with the analysis of 971 Salmonella isolated from different matrixes (human, animal, food or environment) and 33 non-Salmonella strains. The results were compared with the reference identifications, achieving an accuracy of 99.7%. The cost-effective high-throughput genoserotyping assay is performed in 1 day and generates objective results, thanks to the automatic interpretation of raw data using a barcode system. In conclusion, it is fully adapted to the implementation in first line laboratories and meets the requirements of the regulation.

  • Biofilm formation by potentially probiotic Saccharomyces cerevisiae strains
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-23
    Barbara Speranza, Maria Rosaria Corbo, Daniela Campaniello, Clelia Altieri, Milena Sinigaglia, Antonio Bevilacqua

    Four wild strains of Saccharomyces cerevisiae and the collection strain S. cerevisiae var. boulardii ATCC MYA-796 were used as test organisms to study the effect of some environmental conditions on the formation of biofilm by potentially probiotic yeasts. In a first step, the formation of biofilm was studied in four different media (YPD-Yeast Peptone Glucose; diluted YPD; 2% BP, a medium containing only bacteriological peptone; 2% GLC, a medium containing only glucose). Then, the dilution of YPD was combined with pH and temperature through a mixture design to assess the weight of the interaction of the variables; the experiments were done on S. boulardii and on S. cerevisiae strain 4. The dilution of nutrients generally determined an increased biofilm formation, whereas the effect of pH relied upon the strain. For S. cerevisiae strain 4, the highest level of sessile cells was found at pH 4-5, while S. boulardii experienced an enhanced biofilm formation at pH 6.0. Concerning temperature, the highest biofilm formation was found at 25-30°C for both strains. The importance of this work lies in its extension of our knowledge of the effect of different environmental conditions on biofilm formation by potentially probiotic S. cerevisiae strains, as a better understanding of this trait could be an important screening tool into the selection of new multifunctional yeasts.

  • Changes in the microbial communities of air- and water-chilled yellow-feathered broilers during storage at 2 °C
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-23
    Hang Wang, Xiaojie Qin, Xia Li, Xiaoling Wang, Hongwei Gao, Chunhui Zhang

    Carcass chilling is a critical step in broiler processing. Understanding the effect of chilling on the bacterial communities of broilers is important, as these communities may be largely responsible for the spoilage process. This study examined the effect of chilling systems (air chilling [AC] and water chilling [WC]) and subsequent aerobic storage on the microbiota of yellow-feathered broiler carcasses using a high-throughput sequencing technique targeting the V3-V4 region of the 16S RNA gene. Evidence of the clear differences in the microbiota structures between AC and WC carcasses was illustrated by principle coordinates and heat map clustered analyses. The distinctions between the AC and WC carcass bacterial communities were more pronounced during the later storage stages. The major genera on the spoiled AC carcasses were Pseudomonas, Psychrobacter and Shewanella, whereas the major genera on the spoiled WC carcasses were Psychrobacter, Pseudomonas and Carnobacterium. These data suggest that the chilling method has a marked effect on the microbiota composition of yellow-feathered broilers along the entire storage period. The chilling method was also of great importance for surface color. However, there was no significant difference in the sensorial shelf-life of chicken when comparing the chilling methods.

  • Cold Plasma Enhances the Efficacy of Aerosolized Hydrogen Peroxide in Reducing Populations of Salmonella Typhimurium and Listeria innocua on Grape tomatoes, Apples, Cantaloupe and Romaine Lettuce
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-23
    Yuanyuan Song, Xuetong Fan

    In the present study, we investigated whether cold plasma activation affected the efficacy of aerosolized hydrogen peroxide against S. Typhimurium and L. innocua. Stem scars and smooth surfaces of grape tomatoes, surfaces of Granny Smith apples and Romaine lettuce (both midrib and upper leaves) and cantaloupe rinds were inoculated with two-strain cocktails of S. Typhimurium and 3-strain cocktails of L. innocua. The inoculated samples were treated with 7.8% aerosolized H2O2 with and without cold plasma for various times. For all fresh produce items and surfaces, cold plasma significantly (P<0.05) improved the efficacy of aerosolized H2O2 against Salmonella and L. innocua. Without cold plasma activation, H2O2 aerosols only reduced populations of Salmonella by 1.54-3.17 log CFU/piece while H2O2 with cold plasma achieved 2.35-5.50 log CFU/piece reductions of Salmonella. L. innocua was more sensitive to the cold plasma-activated H2O2 than Salmonella. Cold plasma activated H2O2 aerosols reduced Listeria populations by more than 5 log CFU/piece on all types and surfaces of fresh produce except for the tomato stem scar area. Without cold plasma, the reductions by H2O2 were only 1.35-3.77 log CFU/piece. Overall, our results demonstrated that cold plasma activation significantly enhanced the efficacy of H2O2 mist against bacteria on fresh produce.

  • Inactivating foodborne pathogens in apple juice by combined treatment with fumaric acid and ultraviolet-A light, and mechanisms of their synergistic bactericidal action
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-23
    Min-Jin Jeon, Jae-Won Ha

    We evaluated the bactericidal efficacy of the simultaneous application of ultraviolet-A (UV-A) irradiation and fumaric acid (FA) against Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes in apple juice and as well as investigated the effects of this treatment on product quality. Further, we elucidated the mechanisms underlying their synergistic bactericidal action. Simultaneous UV-A light irradiation and 0.1 % FA treatment for 30 min resulted in 6.65-, 6.27-, and 6.49-log CFU/ml reductions in E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively, which involved 3.15, 2.21, and 3.43 log CFU reductions, respectively, and these were attributed to the synergistic action of the combined treatments. Mechanistic investigations suggested that the combined UVA-FA treatment resulted in significantly greater bacterial cell membrane damage and intracellular reactive oxygen species (ROS) generation. UVA-FA treatment for 30 min did not cause significant changes to the color, nonenzymatic browning index, pH, and total phenolic content of apple juice. These results suggest that combined UVA-FA treatment can be effectively used to control foodborne pathogens in apple juice without affecting its quality.

  • Antimicrobial activity of gaseous Citrus limon var Pompia leaf essential oil against Listeria monocytogenes on ricotta salata cheese
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-22
    Francesco Fancello, Giacomo L. Petretto, Salvatore Marceddu, Tullio Venditti, Giorgio Pintore, Giacomo Zara, Ilaria Mannazzu, Marilena Budroni, Severino Zara

    Contamination by Listeria monocytogenes is a particularly challenging problem in the food industry due to the ability of the bacterium to develop under conditions normally used for food preservation. Here, we show that the gaseous phase of Citrus limon var pompia leaf essential oil (hereafter PLEO) exerts specific anti-Listeria activity on ricotta salata cheese stored at 5 °C. The synergic effect of gaseous PLEO treatment and refrigeration was first confirmed in vitro on L. monocytogenes strains treated for 3 h with gaseous PLEO and then stored at 5 °C. Ricotta cheese was then inoculated with L. monocytogenes strains and subjected to hurdle technology with different concentrations of gaseous PLEO. Cell counts revealed gaseous PLEO to exert a bactericidal effect on L. monocytogenes 20600 DSMZ and a bacteriostatic effect on a mix of L. monocytogenes strains. Scanning and transmission electron microscopy analyses of L. monocytogenes cells suggested that gaseous PLEO targets the bacterial cell wall and plasma membrane. Chemical analyses of the liquid and vapor phases of PLEO indicated linalyl acetate to be the predominant compound, followed by limonene and the two isomers of citral, whereas EO composition analysis, although generally in line with previous findings, showed the presence of linalyl acetate for the first time. SPME coupled with gas chromatography confirmed the presence of all crude oil components in the headspace of the box.

  • Evolution of indigenous starter microorganisms and physicochemical parameters in spontaneously fermented beef, horse, wild boar and pork salamis produced under controlled conditions
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-21
    Luca Settanni, Pietro Barbaccia, Adriana Bonanno, Marialetizia Ponte, Rosalia Di Gerlando, Elena Franciosi, Antonino Di Grigoli, Raimondo Gaglio

    The present work was carried out to evaluate the microbiological and physicochemical composition of salamis produced with the meat of beef, horse, wild boar and pork. Salami productions occurred under controlled laboratory conditions to exclude butchery environmental contaminations, without the addition of nitrate and nitrite. All trials were monitored during the ripening (13 °C and 90% relative humidity) extended until 45 d. The evolution of physicochemical parameters showed that beef and pork salamis were characterized by a higher content of branched chain fatty acids (FA) and rumenic acid than horse and wild boar salamis, whereas the last two productions showed higher values of secondary lipid oxidation. Plate counts showed that lactic acid bacteria (LAB), yeasts and coagulase-negative staphylococci (CNS) populations dominated the microbial community of all productions with Lactobacillus and Staphylococcus as most frequently isolated bacteria. The microbial diversity evaluated by MiSeq Illumina showed the presence of members of Gammaproteobacteria phylum, Moraxellaceae family, Acinetobacter, Pseudomonas, Carnobacterium and Enterococcus in all salamis. This study showed the natural evolution of indigenous fermented meat starter cultures and confirmed a higher suitability of horse and beef meat for nitrate/nitrite free salami production due to their hygienic quality at 30 d.

  • Salmonella on Australian cage egg farms: observations from hatching to end of lay
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-21
    Andrea R. McWhorter, Kapil K. Chousalkar

    Single-aged caged layer hen flocks were monitored for Salmonella over the course of their lifetime. Chicks from both flocks were Salmonella negative at hatch and remained negative during rearing. Pullets were transported to production farms at 15 weeks of age. Pre-population dust swabs collected from both production sheds had a high percentage of Salmonella positive samples (80 and 90%). Flocks were sampled at regular intervals until 70-72 weeks of age. The proportion of Salmonella positive samples and mean load detected on eggs was low on both farms. Analysis of dust samples revealed that Salmonella persisted in dust over 8 weeks. Dust total moisture content and water activity appears to influence bacterial persistence. On egg grading equipment, only suction cups prior to egg washing were Salmonella positive (mean proportion Salmonella positive samples 0.13 ± 0.07; mean load of 18.6 ± 12.31 MPN/ml). An egg washing experiment demonstrated that while washing reduced the total Salmonella load from eggshell surfaces, no effect was observed for shell pores. These results demonstrate that despite environmental contamination on farm, Salmonella contamination of eggs is low and is further minimized by washing.

  • Safety and technological application of autochthonous Streptococcus thermophilus cultures in the buffalo Mozzarella cheese
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-20
    Luana Faria Silva, Tássila Nakata Sunakozawa, Daniel Mathias F. Amaral, Tiago Casella, Mara Correa Lelles Nogueira, Juliano De Dea Lindner, Benedetta Botari, Monica Gatti, Ana Lúcia Barretto Penna

    Thermophilic and mesophilic lactic acid bacteria (LAB), such as Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus helveticus, and Lactococcus lactis, play a crucial role in the technological and sensory quality of Mozzarella cheese. In this study, the safety (genes encoding virulence factors and antibiotic resistance) and acidifying activity of autochthonous S. thermophilus cultures were evaluated in order to choose the most suitable strain for industrial application. The safe and good acidifying culture was tested in two buffalo Mozzarella cheese batches: Mozzarella cheeses produced with autochthonous culture (SJRP107) and commercial culture (STM5). The cultivable LAB was evaluated by culture-dependent method (plate counting) and the quantification of S. thermophilus cultures (commercial and autochthonous) were evaluated by culture-independent method RealT-qPCR (real-time quantitative polymerase chain reaction). The texture, physicochemical and proteolytic properties of the Mozzarella cheeses were similar for both batches. The nonstarter LAB count was higher during manufacture than in the storage, and the RealT-qPCR indicated the presence of S. thermophilus culture until the end of storage. S. thermophilus SJRP107 presented high potential for safety application in the production of Mozzarella cheese. Furthermore, considering the culture characteristics and their relationship with product quality, further studies could be helpful to determine their effect on the sensory characteristics of the cheese.

  • Microwave pasteurization of apple juice: Modeling the inactivation of Escherichia coli O157:H7 and Salmonella Typhimurium at 80-90°C
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-18
    Gabriella Mendes-Oliveira, Amanda J. Deering, M. Fernanda San Martin-Gonzalez, Osvaldo H. Campanella

    Although due to their acidity some fruit juices are considered safe, several outbreaks have been reported. For processing fruit juices, microwave heating offers advantages such as shorter come-up time, faster and uniform heating, and energy efficiency. Thus, it could be a beneficial alternative to conventional pasteurization. The objective of this study was to study the inactivation kinetics of Escherichia coli O157:H7 and Salmonella Typhimurium under microwave pasteurization at temperatures between 80 to 90°C, i.e., at conditions that are employed in conventional pasteurization. Inoculated juices were treated at different power levels (600W, 720W) and treatment times (5s, 10s, 15s, 20s, 25s). Time-temperature profiles were obtained by fiber-optic sensors in contact with the samples allowing continuous data collection. The log-logistic and Arrhenius equations were used to account for the influence of the temperature history; thus, resulting in two different modeling approaches that were compared in terms of their prediction abilities. Survival kinetics including non-isothermal conditions were described by a non-linear ordinary differential equation that was numerically solved by the Runge-Kutta method (ode45 in MATLAB ®). The lsqcurvefit function (MATLAB®) was employed to estimate the corresponding survival parameters, which were obtained from freshly made apple juice, whereas the prediction ability of these parameters was evaluated on commercial apple juices. Results indicated that inactivation increased with power level, temperature, and treatment time reaching a microbial reduction up to 7 Log10 cycles. The study is relevant to the food industry because it provides a quantitative tool to predict survival characteristics of pathogens at other non-isothermal processing conditions.

  • Comparison of predicted and impedance determined growth of Listeria innocua in complex food matrices
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-18
    Laura Nyhan, Nicholas Johnson, Máire Begley, Padraic O’Leary, Michael Callanan

    Indirect impedance has been used for the detection and enumeration of bacteria, however there is limited data regarding the ability of the method to measure growth and inhibition of microorganisms in food in response to preservatives. The aim of this study was to evaluate the suitability of the technique to determine maximum growth rates of Listeria innocua (used as a surrogate for Listeria monocytogenes) in complex food matrices to which multiple preservative factors had been applied and assess the suitability of the data for use in predictive microbiology. Growth of L. innocua in laboratory medium (BHI broth) and two food matrices (zucchini purée and béarnaise sauce) under varying conditions of pH (5 & 5.3), water activity (0.93, 0.96 & 0.98) and acetic and propionic acid concentration (0, 1 & 2mM) was monitored by the conductimetric Rapid Automated Bacterial Impedance Technology (R.A.B.I.T) system by means of CO2 emission for up to 120 hours. Growth rates of L. innocua were determined for several conditions across the three test matrices and a good correlation between detection times and initial inoculum level was observed in most cases (R2≥0.82). However, growth of L. innocua was not detected in a large number of conditions and comparison of growth rates determined by indirect impedance to those determined by plate counts indicated that in general, the R.A.B.I.T. system under-estimated growth. This study demonstrates that there are limitations associated with the technology, and as a result the system may be unsuitable for measuring microbial growth rates in complex food matrices under the environmental conditions tested and within the time duration of the study.

  • Shiga toxin-producing Escherichia coli survives storage in wheat flour for two years
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-18
    Alexander Gill, Tanis McMahon, Forest Dussault, Nicholas Petronella

    Wheat flour has recently been recognised as an exposure vehicle for the foodborne pathogen Shiga toxin-producing Escherichia coli (STEC). Wheat flour milled on two sequential production days in October 2016, and implicated in a Canada wide outbreak of STEC O121:H19, was analysed for the presence of STEC in November 2018. Stored in sealed containers at ambient temperature, the water activity of individual flour samples was below 0.5 at 6 months post-milling and remained static or decreased slightly in individual samples during 18 months of additional storage. STEC O121 was isolated, with the same genotype (stx2a, eae, hlyA) and core genome multilocus sequence type as previous flour and clinical isolates associated with the outbreak. The result of this analysis demonstrates the potential for STEC to persist in wheat flour at levels associated with outbreak infections for periods of up to two years. This has implications for the potential for STEC to survive in other foods with low water activity.

  • Quercetin repressed the stress response factor (sigB) and virulence genes (prfA, actA, inlA, and inlC), lower the adhesion, and biofilm development of L. monocytogenes
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-15
    J. Vazquez-Armenta F., A. Hernandez-Oñate M., A. Martinez-Tellez M., A. Lopez-Zavala A., A. Gonzalez-Aguilar G., M. Gutierrez-Pacheco M., F. Ayala-Zavala J.

    The present study explored the effect of quercetin on the expression of virulence genes actA, inlA, inlC, and their regulatory components, sigB and prfA, in L. monocytogenes. Furthermore, the physicochemical changes on the surface, membrane permeability, and biofilm formation of quercetin-treated bacteria were evaluated. An inhibitory dose-dependent effect of quercetin (0.1 – 0.8 mM) was observed on the cell attachment on stainless steel at 2 and 6 h at 37 °C. Quercetin at 0.8 mM prevented the biofilm formation on stainless steel surfaces after 6 h of incubation at 37 °C, while the untreated bacteria formed biofilms with a cell density of 5.1 Log CFU/cm2. The microscopic analysis evidenced that quercetin at 0.2 mM decreased the biovolume and covered area of the attached micro-colonies. Also, sigB, prfA, inlA, inlC, and actA genes were downregulated by 7-29 times lower compared to untreated bacteria. In addition, quercetin decreased the superficial cell charge, increased the membrane permeability, and its surface hydrophobicity. These results demonstrated that quercetin prevented biofilm formation, repressed the genes of stress and virulence of L. monocytogenes and also altered the physicochemical cell properties.

  • Stability of Listeria monocytogenes in non-fat dry milk powder during isothermal treatment and storage
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-15
    Kenneth F. Ballom, Hsieh-Chin Tsai, Mike Taylor, Juming Tang, Mei-Jun Zhu

    Dry dairy powder is a commonly used ingredient for ready-to-eat foods. It has been implicated in multiple foodborne outbreaks. Listeria monocytogenes can survive in low moisture conditions for a long duration. However, there is no information on Listeria survival in dry milk powder during storage and thermal treatments. The objectives of this study were to examine the stability of L. monocytogenes in non-fat dry milk (NFDM) during extended storage and further analyze thermal resistance of L. monocytogenes in NFDM under different water activities (aw) and its thermal stability after 1-year storage. We observed approximately 1.75 and 2.93 log CFU/g reduction of L. monocytogenes in aw 0.25 NFDM over 1-year storage at 4 and 22 °C, respectively. Thermal resistance of L. monocytogenes was inversely related to aw, and the inactivation kinetic curves of L. monocytogenes in NFDM at target aw showed a log-linear trend under all tested conditions. For aw 0.25, 0.30, and 0.45 NFDM, the ranges of D-values, were 66.2 - 21.3, 33.5 - 9.4, and 14.6- 4.3 min at 70, 75 and 80 °C, respectively. The z-values for L. monocytogenes in NFDM at aw 0.25-0.45 were 14.62 - 15.95 °C. Furthermore, the thermal stability of L. monocytogenes in aw 0.25 NFDM post 6-month or 12-month storage under refrigerated or ambient storage did not deviate much from that in NFDM prior to the storage. Data indicated that a 60-min heat treatment at 80 °C resulted in ∼ 5-log reduction of L. monocytogenes in NFDM of aw 0.30. This provides a promising intervention strategy to enhance bactericidal efficacy of thermal treatment while maintaining the quality of milk powder.

  • Brettanomyces bruxellensis phenotypic diversity, tolerance to wine stress and wine spoilage ability
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-15
    Alice Cibrario, Cécile Miot-Sertier, Margot Paulin, Bastien Bullier, Laurent Riquier, Marie Claire Perello, Gilles de Revel, Warren Albertin, Isabelle Masneuf-Pomarède, Patricia Ballestra, Marguerite Dols-Lafargue

    Brettanomyces bruxellensis is a yeast species found in many fermented matrices. A high level of genetic diversity prevails in this species and was recently connected with tolerance to sulfur dioxide, the main preservative used in wine. We therefore examine other phenotypes that may modulate the ability of the species to spoil wine, in a selection of representative strains. The species shows a fairly high homogeneity with respect to the carbohydrates that can support growth, but more diverse behaviors regarding tolerance to low pH or ethanol. Thought no clear link can be drawn with genotype, some strains appear more tolerant than the others, mainly in the AWRI1499 like genetic group. Volatile phenol production is ubiquitous within the species, independent from yeast growth profile and not affected by the nature of the growth substrate. The specific production. n rate of volatile phenol production raises in case of increased aeration. It is little affected by pH decrease until 3.0 or by ethanol concentration increase up to 12% vol, but it decreased in case of increased constraint (pH <3.0, Ethanol ≥14% vol) or combination of constraints. All the strain studied have thus the ability to spoil wine but some outstanding dangerous strains can even spoil the wine with high level of constrainst.

  • Fungal communities in rice cultivated in different Brazilian agroclimatic zones: from field to market
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-15
    Aline M. Katsurayama, Ligia M. Martins, Beatriz T. Iamanaka, Maria Helena P. Fungaro, Josué J. Silva, John I. Pitt, Jens C. Frisvad, Marta H. Taniwaki

    Rice is one of the most consumed cereals in Brazil and around the world. Due to the major health impact of rice consumption on populations, studies about its quality have great importance. The present study determined the mycobiota of soil, field, processing and market rice samples from two production systems in Brazil, dryland in the state of Maranhão and wetland in the state of Rio Grande do Sul. These areas are distinct agroclimatic zones. A total of 171 rice and 23 soil samples were analyzed. A high differentiation was observed in the composition of the fungal communities found in the two production systems, as the wetland presented greater fungal incidence and biodiversity. It was observed that toxigenic species from Aspergillus section Flavi and Fusarium, present in the field, may infect rice grains pre or postharvest and may persist into the final product.

  • Development of a multiplex real-time PCR to differentiate the four major Listeria monocytogenes serotypes in isolates from meat processing plants
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-11
    Alberto Alía, María J. Andrade, Juan J. Córdoba, Irene Martín, Alicia Rodríguez

    Listeria monocytogenes is an important foodborne pathogen, causative agent of listeriosis. The epidemiology and persistence of this bacterium in meat processing plants may be related to its serotype, so it is of utmost importance to carry out a correct differentiation of L. monocytogenes serotypes. The objective of this study was to develop a unique quadruplex real-time quantitative PCR (qPCR) method able to differentiate the four most predominant and worrying L. monocytogenes serotypes (1/2a, 1/2b, 1/2c and 4b) in isolates from meat processing plants and ready-to-eat (RTE) dry-cured meat products. The design of specific primers and probes was based on the lmo0737, lmo0308, ORFC (locus genomically equivalent to gltA-gltB) and ORF2110 genes. A qPCR based on a fragment of the 16S rRNA gene was used to ensure the amplification of Listeria spp. genomic DNA. The standard curves showed efficiency values ranging between 92.3 % and 105.8 % and, R2 values > 0.98. The specificity of the method was also confirmed by the comparison of the results with those obtained by a previously reported conventional multiplex PCR. In addition, none of the strains which were not ascribed to L. monocytogenes amplified any of the target genes related to the four major serotypes of this pathogenic species. The qPCR, therefore, provides a sensitive, specific and rapid tool for identifying the L. monocytogenes serotypes 1/2a, 1/2b, 1/2c and 4b. This method could be very useful for identifying sources of L. monocytogenes contamination in the meat industry or for epidemiological monitoring of persistent strains throughout the processing of RTE meat products.

  • Biocontrol ability and action mechanism of Metschnikowia citriensis against Geotrichum citri-aurantii causing sour rot of postharvest citrus fruit
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-08
    Shupei Wang, Changqing Ruan, Lanhua Yi, Lili Deng, Shixiang Yao, Kaifang Zeng

    This study investigated the biocontrol efficiency of Metschnikowia citriensis strain FL01 against Geotrichum citri-aurantii, and evaluated possible mechanisms. The results showed that M. citriensis could effectively control the development of sour rot, and significantly inhibit the mycelial growth and spore germination of G. citri-aurantii. The population dynamics results and Scanning electron microscopy (SEM) analysis indicated that M. citriensis could rapidly colonize wounds and tightly adhere to the surface of the wounds to compete with G. citri-aurantii for nutrition and space. M. citriensis also showed the biofilm formation action in vitro. The response of G. citri-aurantii to different components of M. citriensis culture showed that only the yeast cells but not the extracellular metabolites and the volatile organic compounds (VOCs) exhibited inhibitory effect on the growth of G. citri-aurantii. M. citriensis adhered to the hyphae of G. citri-aurantii loosely and sparsely, and the production of lytic enzymes β-1, 3-glucanase (GLU) and Chitinase (CHI) could not be induced by G. citri-auranti. Iron affected the pulcherrimin pigment production and antagonism of M. citriensis indicating iron depletion as the most important antagonistic mechanism. Besides, M. citriensis also induced resistance of fruit against sour rot. These results suggested that M. citriensis could be used as the potential alternative of fungicides to control postharvest pathogens on citrus fruit.

  • Salmonella inactivation and cross-contamination on cherry and grape tomatoes under simulated wash conditions
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-06
    Samantha Bolten, Ganyu Gu, Yaguang Luo, Sam Van Haute, Bin Zhou, Pat Millner, Shirley A. Micallef, Xiangwu Nou

    Washing in chlorinated water is widely practiced for commercial fresh produce processing. While known as an effective tool for mitigating food safety risks, chlorine washing could also represent an opportunity for spreading microbial contaminations under sub-optimal operating conditions. This study evaluated Salmonella inactivation and cross-contamination in a simulated washing process of cherry and grape tomatoes. Commercially harvested tomatoes and the associated inedible plant matter (debris) were differentially inoculated with kanamycin resistant (KanR) or rifampin resistant (RifR) Salmonella strains, and washed together with uninoculated tomatoes in simulated packinghouse dump tank (flume) wash water. Washing in chlorinated water resulted significantly higher Salmonella reduction on tomatoes than on debris, achieving 2-3 log reduction on tomatoes and about 1 log on debris. Cross-contamination by Salmonella on tomatoes was significantly reduced in the presence of 25-150 mg/L free chlorine, although sporadic cross-contamination on tomatoes was detected when tomatoes and debris were inoculated at high population density. The majority of the sporadic cross-contaminations originated from Salmonella inoculated on debris. These findings suggested that debris could be a potentially significant source of contamination during commercial tomato washing.

  • Application of chlorine dioxide and peroxyacetic acid during spray chilling as a potential antimicrobial intervention for beef carcasses
    Food Microbiol. (IF 4.089) Pub Date : 2019-10-31
    Chawalit Kocharunchitt, Lyndal Mellefont, John P. Bowman, Tom Ross

    Enteric pathogens such as Shiga-toxin producing Escherichia coli (STEC) and Salmonella spp. continue to be a major food safety concern for the beef industry. Currently, no single method is completely effective in controlling these pathogens during carcass processing. Previous research, however, suggested that STEC might become more susceptible to oxidative damage when exposed to carcass chilling (King et al., 2016). We aimed to test that hypothesis by evaluating the antimicrobial effects of an oxidant (chlorine dioxide, ClO2 or peroxyacetic acid, PAA) on beef meat during a simulated spray chilling process (sprayed for 4 s every 15 min for 36 cycles) and/or when applied (sprayed for 144 s) prior to spray chilling with water. In all experiments, the inactivating effects of oxidants were greatest on fat surfaces and much less effective on lean surfaces. ClO2 at 15 ppm, a non-lethal level for E. coli under optimal growth conditions, caused higher log reductions in E. coli numbers (approximately 3-log reduction) when applied during spray chilling than when applied immediately prior to ‘normal’ spray chilling (approximately 1-log reduction). This confirms the hypothesis that E. coli are more susceptible to oxidative stress during spray chilling. In subsequent studies, both ClO2 and PAA at lethal levels (at ≥20 and ≥200 ppm, respectively) applied during spray chilling resulted in pronounced inactivation of both E. coli and Salmonella enterica strains, achieving a ≥4-log reduction at the end of chilling. These results indicate that an oxidant-based application during spray chilling as an antimicrobial intervention could be effective to minimise the problems associated with enteric pathogen contamination on beef meat.

  • Effect of Polymer and Glass Physicochemical Properties on MS2 Recovery from Food Contact Surfaces
    Food Microbiol. (IF 4.089) Pub Date : 2019-10-31
    R. Yan, Y. Wang, T.V. Duncan, Y.C. Shieh

    Viruses are transmissible via their interaction with contact surfaces of food containers or tools. This study evaluated the recoveries of MS2 coliphage, a virus surrogate, from polypropylene (PP), polyvinyl chloride (PVC), polyethylene (PE), and glass (borosilicate and soda lime), as influenced by the surface chemistry and topography. MS2 (5-6 logs) in PBS with 1% TSB was inoculated onto each of 9 different surfaces, 24-h cold-incubated, and recovery was quantified by infectivity. The order of MS2 recovery efficiency from smooth surfaces was PP > PE ≥ soda lime glass, which classified into 3 ANOVA groups, p = 0.05. The MS2 recovery ratios of smooth vs. rough surfaces were 1.4 to 1.5. Atomic force microscopy revealed 21-nm diam pinholes (<28-nm of MS2 size) in the borosilicate glass. The lowest and highest MS2 recoveries among the 9 surfaces were demonstreated by the hole-bearing borosilicate glass (34±8 %) and smooth PP (69±14 %) respectively. Generally greater MS2 recovery was obtained from smooth PP and PE surfaces compared to glass, but topographic alterations (pinholes or increased roughness) decreased recovery possibly by trapping the viruses.

  • Small scale fungal community differentiation in a vineyard system
    Food Microbiol. (IF 4.089) Pub Date : 2019-10-30
    Sarah J. Knight, Ophir Karon, Matthew R. Goddard

    Microbes influence the quality of agricultural commodities and contribute to their distinctive sensorial attributes. Increasingly studies have demonstrated not only differential geographic patterns in microbial communities and populations, but that these contribute to valuable regionally distinct agricultural product identities, the most well-known example being wine. However, little is understood about microbial geographic patterns at scales of less than 100 km. For wine, single vineyards are the smallest (and most valuable) scale at which wine is asserted to differ; however, it is unknown whether microbes play any role in agricultural produce differentiation at this scale. Here we investigate whether vineyard fungal communities and yeast populations driving the spontaneous fermentation of fruit from these same vineyards are differentiated using metagenomics and population genetics. Significant differentiation of fungal communities was revealed between four Central Otago (New Zealand) Pinot Noir vineyard sites. However, there was no vineyard demarcation between fermenting populations of S. cerevisiae. Overall, this provides evidence that vineyard microbiomes potentially contribute to vineyard specific attributes in wine. Understanding the scale at which microbial communities are differentiated, and how these communities influence food product attributes has direct economic implications for industry and could inform sustainable management practices that maintain and enhance microbial diversity.

  • Role of DNA repair in Bacillus subtilis spore resistance to high energy and low energy electron beam treatments
    Food Microbiol. (IF 4.089) Pub Date : 2019-10-30
    Yifan Zhang, Nina Huber, Ralf Moeller, Jörg Stülke, Barbora Dubovcova, Georgios Akepsimaidis, Nicolas Meneses, David Drissner, Alexander Mathys

    Bacillus subtilis spore inactivation mechanisms under low energy electron beam (LEEB) and high energy electron beam (HEEB) treatment were investigated using seven mutants lacking specific DNA repair mechanisms. The results showed that most of the DNA repair-deficient mutants, including ΔrecA, ΔKu ΔligD, Δexo Δnfo, ΔuvrAB and ΔsbcDC, had reduced resistances towards electron beam (EB) treatments at all investigated energy levels (80 keV, 200 keV and 10 MeV) compared to their wild type (p < 0.05). This result suggested DNA damage was induced during EB treatments. The mutant lacking recA showed the lowest resistance, followed by the mutant lacking Ku and ligD. These findings indicated that recA, Ku and ligD and their associated DNA repair mechanisms, namely, homologous recombination and non-homologous end joining, play important roles in spore survival under EB treatment. Furthermore, exoA, nfo, uvrAB, splB, polY1 and polY2, which are involved in nucleotide damage repair/removal, showed different levels of effects on spore resistance under EB treatment. Finally, the results suggested that HEEB and LEEB inactivate B. subtilis spores through similar mechanisms. This research will provide a better understanding of how EB technologies inactivate B. subtilis spores and will contribute to the application of these technologies as a non-thermal, gentle spore control approach.

  • Persistence and reservoirs of Saccharomyces cerevisiae biodiversity in different vineyard niches.
    Food Microbiol. (IF 4.089) Pub Date : 2019-11-11
    Magalí Lucía González,María Elena Sturm,María Cecilia Lerena,María Cecilia Rojo,Selva Valeria Chimeno,Mariana Combina,Laura Analía Mercado

  • Strawberry sanitization by peracetic acid washing and its effect on fruit quality.
    Food Microbiol. (IF 4.089) Pub Date : 2019-06-17
    Iolanda Nicolau-Lapeña,Maribel Abadias,Gloria Bobo,Ingrid Aguiló-Aguayo,Tomás Lafarga,Inmaculada Viñas

    The risk posed by outbreaks associated with strawberries together with the safety issues of by-products from chlorine disinfection in the fruit industry has led to a search for alternative sanitizers. The disinfection capacity of peracetic acid (PA) at three concentrations (20, 40 and 80 ppm) and washing times (1 and 2 min) was compared to sodium hypochlorite (200 ppm) (NaClO) treatments and a water control, and its influence on the physico-chemical, biochemical and nutritional quality of strawberries was also studied. Counts on total aerobic mesophilic microorganisms were comparable between NaClO and PA. For yeasts and molds, only NaClO and 80 ppm PA reduced contamination in washing water, but no differences wereobserved in strawberries. Artificially inoculated L.innocua was reduced by at least 4 log cfu/g in strawberry by all the PA treatments, except at 20 ppm PA for 1 min. Total soluble solids, pH, titratable acidity, antioxidant activity and total phenolic content values were maintained after all treatments. Only anthocyanin content was affected. Treatments of 20 and 40 ppm PA did not significantly affect fruit color, and there were no losses on strawberry firmness. PA, as a GRAS substance that has shown potential to reduce microorganisms present in strawberries without any major physicochemical or sensorial alteration, could be a suitable alternative to chlorine disinfection.

  • 更新日期:2019-11-01
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上海纽约大学William Glover