Volatile compounds and odour characteristics of five edible seaweeds preserved by high pressure processing: Changes during refrigerated storage
Graphical abstract
Introduction
Bioactive compounds and nutrients present in seaweeds such as polyunsaturated fatty acids, phenolic compounds, fibre, vitamins, amino acids and minerals endorse their relevant contribution to the traditional diet of many Asian countries [[1], [2], [3], [4]]. In Western countries, seaweed-derived functional foods, nutraceuticals and ingredients are appealing for consumers on the basis of their health benefits [[5], [6], [7], [8]].
Shelf life of seaweeds is limited by their high moisture content which allows profuse microbial growth in such a nutrient-rich medium [9], in spite of the inhibitory compounds they contain [10,11]. Some pathogenic species have been found among the microbial contaminants of seaweeds [12], and may pose serious risks for consumers [13]. Seaweed preservation by traditional procedures such as drying or salting lowers the water activity value [14,15], but does not guarantee microbiological safety. In fact, the levels of most microbial groups did not decline during refrigerated storage of salted seaweeds [15,16].
High pressure processing (HPP) is a non-thermal procedure which offers advantages in relation to the improvement of the microbiological safety and the preservation of the nutritional properties of foods [[17], [18], [19]]. Treatments at 400 or 600 MPa for 5 min were shown to be successful in assuring the microbiological safety and extending the shelf life of Laminaria ochroleuca up to 180 days. HPP restrained growth of L. ochroleuca microbiota maintaining seaweed characteristics such as pH value, colour, texture, polyphenol content and antioxidant capacity during refrigerated storage [16]. In a later study, satisfactory results regarding the microbiological quality and extension of shelf life were obtained for seaweeds Chondrus crispus, Codium fragile, Himanthalia elongata, Ulva lactuca and Undaria pinnatifida by applying HPP treatments of 400 or 600 MPa for 5 min. From the microbiological point of view, shelf life periods of at least 180 days were achieved by 600 MPa treatments for all the assayed seaweeds [20].
Sensory characteristics of seaweeds, an appealing trait for consumers, tend to decline along refrigerated storage due to decay of exogenous and endogenous origin. Contaminating bacteria and fungi growing on seaweeds affect their aroma, colour and texture during storage [9,15,16]. Concurrently, seaweed physiological processes may contribute to alter their volatile fraction and odour characteristics during prolonged storage [21,22]. Seaweeds release volatile compounds to the surrounding ecosystems which may act as sexual pheromones, deterrents or chemical defenses against herbivores, feeding attractants and incitants, inhibitors of bacteria and fungi, and suppressors of competitive neighbours [23,24]. The volatile compounds found in seaweeds depend on the species, the geographical origin, the time of harvest, and the method used for extraction prior to analysis by gas chromatography–mass spectrometry (GC–MS), such as dynamic headspace extraction [25,26], distillation-solvent extraction [27,28] or solid-phase microextraction [[29], [30], [31]]. In a previous study, HPP of L. ochroleuca at 400 or 600 MPa contributed to minimize changes in its volatile fraction during refrigerated storage for 180 days, maintaining high odour acceptance scores [31].
There is a need for research on the effect of processing and preservation techniques on different aspects of seaweed quality, including their sensory characteristics and volatile compound composition [3,32,33]. Relationships between flavour, odour and volatile profile of some edible seaweeds before and after storage have been reported in previous studies [[31], [32], [33]]. Flavour richness of P. palmata correlated not only with the concentration of free amino acids glutamate and aspartate but also with the levels of volatile compounds 1-penten-3-ol, and (E)-2-hexenal [33]. It must be noted that the perception of umami taste of seaweeds does not only depend on the glutamate content but also on how other tastes and volatile compounds influence the taste experience [34].
Satisfactory preservation of L. ochroleuca odour characteristics was achieved by means of HPP treatments at 400 and 600 MPa for 5 min [31]. However, other seaweed species with different physiological and metabolic traits might behave differently when submitted to HPP followed by prolonged refrigerated storage. Although microbial growth was efficiently controlled by HPP during storage of C. crispus, C. fragile, H. elongata, U. lactuca and U. pinnatifida [20], information on the changes in their volatile fraction and odour characteristics along refrigerated storage is lacking. The objective of the present study was to investigate the effect of HPP and refrigerated storage on the volatile compounds and the odour characteristics of those five edible seaweeds.
Section snippets
Seaweeds and HPP treatments
C. crispus (CC, red seaweed, Irish moss), C. fragile (CF, green seaweed, green sea fingers), U. lactuca (UL, green seaweed, sea lettuce), H. elongata (HE, brown seaweed, sea spaghetti) and U. pinnatifida (UP, brown seaweed, wakame) were collected in spring at Galicia (NW Spain) coastal areas and transported under refrigeration to the laboratory in Madrid (Spain). Two batches of fresh seaweeds, collected three weeks apart, were used for experiments. On arrival to the laboratory (day 1 after
Diversity of volatile compounds in seaweeds
A total of 133 different volatile compounds were detected in control seaweeds on day 2 after collection (Table 1). Out of them, 121 compounds could be identified and were included into 12 chemical groups. Aldehydes (24) and alcohols (23) were the groups harbouring the highest number of volatile compounds, followed by ketones (18), hydrocarbons (17) and benzene compounds (14). Among seaweeds, C. crispus (89) and U. lactuca (79) were the species showing the highest diversity of volatile
Conclusions
A high diversity in the volatile compounds of five edible seaweeds was recorded in the present study. During refrigerated storage of control seaweeds, the levels of alcohols, benzene compounds and S-compounds increased while those of hydrocarbons, aldehydes and acids decreased, with differences in the fate of volatile compounds depending on the seaweed species. HPP at 400 or 600 MPa had a more marked effect immediately after treatment on the volatile compounds of C. crispus, C. fragile and U.
CRediT authorship contribution statement
Olga López-Pérez: Conception and design, Analysis and interpretation of data, Statistical treatment. Ana del Olmo: Conception and design, Analysis and interpretation of data, Statistical treatment. Antonia Picon: Conception and design, Writing and revising the paper, Final approval, Obtaining of funding. Manuel Nuñez: Conception and design, Writing and revising the paper, Final approval, Obtaining of funding.
Statement of informed consent, human/animal rights
No conflicts, informed consent, or human or animal rights are applicable to this study.
Declaration of competing interest
I declare on behalf of all co-authors that there is not any conflict of interest regarding the contents and funding sources of the paper entitled “Volatile compounds and odour characteristics of five edible seaweeds preserved by high pressure processing: changes during refrigerated storage”, by Olga López-Pérez et al., in submission for publication at Algal Research – Biomass, Biofuels and Bioproducts.
Acknowledgements
This research was supported by project AGL2013-42911-R (Ministerio de Economía y Competitividad, Spain). The courageousness and camaraderie from Ana del Olmo during the performance of this study is acknowledged by the rest of authors.
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