Pyrosequencing-based analysis of the bacterial community during fermentation of Alaska pollock sikhae: traditional Korean seafood

Abstract

We analyzed the bacterial community of Alaska pollock sikhae, a traditional Korean food made by natural fermentation with Alaska pollock, utilizing pyrosequencing. We fermented the Alaska pollock sikhae at two different temperatures (10 C and 20 C). Before fermentations, the bacterial community was varied. After fermentations, however, Lactobacillus sakei became dominant. The Alaska pollock sikhae sample before fermentations contained only 2% L. sakei, but the sample on day 6 of fermentation at 10 C comprised 74% L. sakei (90% at 20 C). In addition, we observed a reduction in the composition of unpreferred bacterial species for foods after fermentation. The composition of unpreferred bacterial species was more than 30% of total reads in samples before fermentation and decreased to less than 0.2% after fermentation. This result suggested that the fermentation of Alaska pollock sikhae can be beneficial for food safety. Alaska pollock sikhae might be a favorable habitat for L. sakei. Our study is the first report illustrating the alteration of the bacterial community of Alaska pollock sikhae during fermentation utilizing pyrosequencing analysis.Key words: Alaska pollock sikhae; bacterial community analysis; Lactobacillus sakei; pyrosequencing analysis IntroductionNumerous fermented foods are popular in Korea. Korean fermented foods were designed for long-term storage, to supplement various nutrients, and to provide featured flavors. Jeotgal and sikhae are both traditional fermented seafoods made for long-term storage (Rhee et al., 2011). While jeotgal contains a relatively high concentration of salt [generally 20 30% (w/w)], sikhae uses a low concentration of salt [ 7%] (Cha et al., 2004; Jung et al., 2013a, b;Guan et al., 2011;Lee et al., 2014). In contrast to jeotgal, sikhae contains grains that provide abundant carbon sources to microbes. Gajami-sikhae, Alaska pollock sikhae, and squid sikhae are the three most popular Korean sikhae. In addition to salt and fish (Alaska pollock), Alaska pollock sikhae is composed of cooked grains, white radish, red pepper powder, malt, garlic, and ginger. Alaska pollock sikhae is mainly divided into Kangwondo-and Kyoungsangdo-style recipes. While Kyoungsangdo-style recipes use dried Alaska pollock, undried fish are utilized for the Kangwondo-style recipes. Despite its importance as a Korean fermented food, there is limited research regarding sikhae and our understanding of the fermentation mechanisms of sikhae is largely incomplete.Novel bacterial strains were isolated from sikhae, mainly from gajami-sikhae (Kim et al., 2009;Jung et al., 2012a;Shin et al., 2011;Park et al., 2013Park et al., , 2014. Alishewanella jeotgali MS1 T was isolated from gajami-sikhae and its genome was fully sequenced (Kim et al., 2009;Jung et al., 2012a). Shin and co-workers isolated Leutobacter celer NAL101 T from gajami-sikhae (Shin et al., 2011). They suggested that the gajami-sikhae habitat might not be the optimal growth condition for the NAL101 T strain (Shin et al., 2011). Park and colleagues iso...

Exploring the Brine Microbiota of a Traditional Norwegian Fermented Fish Product (Rakfisk) from Six Different Producers during Two Consecutive Seasonal Productions

“…This species is often associated with various meat fermentations [36] and one of relatively few LAB able to grow in the salt concentrations and the ripening temperatures applied during rakfisk fermentations [37,38]. L. sakei was also found to be the dominant LAB in sikhae and gajami-sikhae, mild-salted fermented fish products from Korea [15]. The Chinese product Suan Yu , with some similarities to rakfisk fermentation [10], but fermented at higher temperature, was shown by microbiota analysis to be quickly dominated by Firmicutes and lactobacilli with higher temperature preferences, such as L. plantarum [39].…”

“…This taxon has been found dominant in shellfish [18] and in cured skate [41]. However, several studies found Gammaproteobacteria as a non-dominant part of the bacteria in fermented food [42,43,44] or found that the domination of this taxon has been replaced by Firmicutes towards the end of the fermentation [15,45,46]. In our study, Gammaproteobacteria was dominating in the brine when rakfisk was produced with a high salinity combined with a low ripening temperature.…”

“…Psychrobacter species are halotolerant, have a lower growth optimum temperature than for instance L. sakei [54,55] and are therefore suited to grow in rakfisk brine. Interestingly, Psychrobacter was found to be the third most dominant genera (at 15%) after fermentation in the aforementioned Korean fermented fish product sikhae, dominated by L. sakei [15]. Notably, a Psychrobacter strain has been used as a starter culture for fish sauce fermentation due its proteolytic properties [56].…”

“…Globally, few fermented fish products share similarities in the manufacture process with rakfisk , at least described in the scientific literature. However, sikhae (Korea) [15], Suan Yu (China) [10], and Chouguiyu (China) [6,16] are all mildly salted fish, fermented in brine at relatively low temperatures. All these fermentations seem to be dominated by salt- and cold-tolerant lactobacilli, in some cases determined to be Lactobacillus sakei [6,15].…”

“…Hypervariable regions in the 16S ribosomal RNA (rRNA) gene are the most common target for analyzing diversity in a variety of complex microbial communities, including food [17], with several examples from seafood fermentations [7,15,18].…”