Effect of processing on microbial safety of wild pepper (Piper borbonense) from Reunion Island

Highlights

• Variations in microbial counts and fungal diversity were observed on pepper berries.

• Blanching was efficient in decreasing microbial counts while drying had a low impact.

• Sweating lead to an increase in microbial counts and thus should be avoided.

• Mycotoxins were detected in only one sample and at a very low level.

Abstract

The management of microbial contamination is an important issue in spice trade. For common domesticated black pepper (Piper spp.), the control relies mainly on post-process decontamination. The aim of the present study was to examine microbial contamination of wild pepper (Piper borbonense) from Reunion Island and investigate the effects of different processing paths on microbiological quality and fungal ecology. The fresh pepper microbial counts ranged from 4.6 to 6.8 log CFUg⁻¹. Blanching had a positive significant impact on the microbiological quality of pepper whereas sweating led to microbial growth up to 5 log CFUg⁻¹ and, therefore, should be avoided. Microbial counts for dried pepper were 1.33 log CFUg⁻¹; 3.37 log CFUg⁻¹; 1.67 log CFUg⁻¹ and 1.3 log CFUg⁻¹ for coliforms, TAMB, Staphylococcus, yeast and moulds, respectively. Potential mycotoxin producers were identified from pepper samples but aflatoxins and ochratoxin A levels detected were far below the regulation limits. The initial diversity of fungal contamination is prominent for the final quality of pepper in contrast to the impact of processes. The revisited wet process (blanching then drying), which positively affected all microbial loads, could be a good option for pepper transformation.

Introduction

Spices and herbs are used worldwide to enhance food flavour. Whereas herbs are obtained from the leaves, spices cover roots, stems, bulbs, barks, berries or seeds. Among those, black pepper (Piper nigrum) is one of the most extensively used spice in the world. In 2017, 690 000 tons of pepper were produced; nearly one-third of which was produced by Vietnam, the leading producer, ahead of Indonesia and India (FAOSTAT, 2019).

The highest demand of pepper comes from Europe and North America, where pepper is used for food industry, institutional catering and home-consumption. Therefore, the different geographical locations for production and consumption leads to high trade volumes. Dried black pepper trade accounted for twenty per cent of all spice imports in 2002 (Mokshapathy & Yogesh, 2013). Wild peppers represent an extremely low amount of trade, but their high sensory characteristics put them in a prominent place regarding their commercial value. For instance, black pepper is sold for around 30 euros per kg, when Tsiprifery, a wild Malagasy pepper, reaches 200 euros/kg in French delicatessens (Razafimandimby et al., 2017). Piper borbonense, the wild pepper from Reunion Island, though offering worthwhile potential regarding its original chemical composition (Weil, Shum, Meot, Boulanger, & Bohuon, 2017) is not cultivated, neither processed, nor commercialised yet.

Legal requirements for the entrance of pepper in the European market (CBI, 2019) are for the product to comply with maximum levels of mycotoxins, in particular aflatoxin and ochratoxin, and microbial contamination levels. For instance, in 2018, a total of 17 batches of black pepper received a border control notification, among those 9 were subjected to withdrawal, due to the positive detection of Salmonella (RASFF, 2019). Thus, many studies have focused on the ability of Salmonella to grow or survive on black pepper over an extended storage time (Keller, VanDoren, Grasso, & Halik, 2013). However microbial contamination levels of black pepper is not restricted to pathogens, with the detection of total mesophilic bacteria in the range of 2–8 log CFUg⁻¹ (Chitrakar, Zhang, & Adhikari, 2018; Fogele, Granta, Valcina, & Berzins, 2018; Garbowska, Berthold-Pluta, & Stasiak-Rozanska, 2015; Klimešová et al., 2015; Mckee, 1995; Plany et al., 2018). Bacillus spp. or Clostridium perfringens or other spore-forming bacteria are often reported, as well as Staphylococci and Enterobacteria. Both Salmonella and Gram-positive bacteria counts did not decrease significantly over storage (Thanh et al., 2018). Assessment of mycological quality and mycotoxin contamination of black pepper showed that Aspergillus flavus, Aspergillus parasiticus, Aspergillus niger and Penicillium spp. were the main potentially mycotoxinogenous fungi associated to pepper (El Mahgubi et al., 2013; Fogele et al., 2018; Yogendrarajah, Deschuyffeleer, et al., 2014). As a consequence, aflatoxins, ochratoxin and other mycotoxins were occasionally detected at low concentrations, therefore, the risk associated to black pepper consumption was considered low (Yogendrarajah, Deschuyffeleer, et al., 2014; Yogendrarajah et al., 2015; Yogendrarajah, Jacxsens, et al., 2014; Yogendrarajah et al., 2016). In contrast to black pepper, there is no data concerning microbial contamination of wild pepper, such as P. borbonense.

The management of microbial contamination in spices relies mainly on good practices, but inactivation of bacteria may be performed. To this end, non-thermal methods are of high interest as their impact on aromatic compounds is low. Superheated steam, vacuum-steam pasteurization, radio-frequency heating, microwave- or gamma-irradiation have shown to be efficient to decrease Salmonella or Escherichia coli populations (Ban et al., 2018; Jeevitha, Sowbhagya, & Hebbar, 2016; Jeong & Kang, 2014; Shah, Asa, Sherwood, Graber, & Bergholz, 2017; Song et al., 2014). Another approach is to investigate processing practices in the light of microbiological contaminants. In Madagascar, wild peppers are processed according to ‘‘dry” and ‘‘wet” processes (Weil et al., 2014). The ‘‘dry” process only consists of single drying, whereas the ‘‘wet” process includes blanching and sweating prior to drying. Blanching consists of dipping pepper berries in hot or boiling water for a few minutes. According to Dhas and Korikanthimath (2003), it is used not only to remove impurities and increase the speed of drying but also to decrease the microbial load. Traditionally, sweating, i.e. keeping the hot blanched pepper in a blanket for 24 h is used in Madagascar to brown pepper and is hypothesized to develop its aroma (as for vanilla). Drying is performed to reduce water content and stabilize pepper for future conservation by limiting microbial growth. Previous studies (Weil et al., 2017) showed, chemical-sensorial criteria such as piperine and essential oil contents were quite resistant to the process. Therefore, the choice of the process could be monitored according to sanitary considerations. There is no literature investigating the impact of these processing practices on microbial contaminants. The aim of this study was to examine the microbial contamination of wild pepper (P. borbonense) from Reunion Island and investigate the effects of different processing paths on the microbiological quality.