Microbial Successions and Metabolite Changes during Fermentation of Salted Shrimp (Saeu-Jeot) with Different Salt Concentrations

Abstract

To investigate the effects of salt concentration on saeu-jeot (salted shrimp) fermentation, four sets of saeu-jeot samples with 20%, 24%, 28%, and 32% salt concentrations were prepared, and the pH, bacterial and archaeal abundances, bacterial communities, and metabolites were monitored during the entire fermentation period. Quantitative PCR showed that Bacteria were much more abundant than Archaea in all saeu-jeot samples, suggesting that bacterial populations play more important roles than archaeal populations even in highly salted samples. Community analysis indicated that Vibrio, Photobacterium, Psychrobacter, Pseudoalteromonas, and Enterovibrio were identified as the initially dominant genera, and the bacterial successions were significantly different depending on the salt concentration. During the early fermentation period, Salinivibrio predominated in the 20% salted samples, whereas Staphylococcus, Halomonas, and Salimicrobium predominated in the 24% salted samples; eventually, Halanaerobium predominated in the 20% and 24% salted samples. The initially dominant genera gradually decreased as the fermentation progressed in the 28% and 32% salted samples, and eventually Salimicrobium became predominant in the 28% salted samples. However, the initially dominant genera still remained until the end of fermentation in the 32% salted samples. Metabolite analysis showed that the amino acid profile and the initial glycerol increase were similar in all saeu-jeot samples regardless of the salt concentration. After 30–80 days of fermentation, the levels of acetate, butyrate, and methylamines in the 20% and 24% salted samples increased with the growth of Halanaerobium, even though the amino acid concentrations steadily increased until approximately 80–107 days of fermentation. This study suggests that a range of 24–28% salt concentration in saeu-jeot fermentation is appropriate for the production of safe and tasty saeu-jeot.

Bacterial community dynamics and metabolite changes in myeolchi-aekjeot, a Korean traditional fermented fish sauce, during fermentation

“…Three sets of myeolchi-aekjeot (MA) samples with approximately 25% (w/v) salt concentration were prepared in triplicate using anchovies (E. japonicus) of different lengths (5-8 cm, small (S); 8-10 cm, medium (M); 10-13 cm, large (L)) as described previously Lee et al, 2014a). Because the average size of anchovies harvested from Korean waters depends on the fishing season, the three sets of MA samples were prepared independently at different times of the year.…”

“…The centrifugation supernatants were stored separately at −80°C for respective metabolite analysis. Bacterial abundances in MA samples were estimated using quantitative PCR (qPCR) according to a previously described method (Lee et al, 2014a). NaCl concentrations in MA samples were measured according to the Mohr method (AOAC, 2000).…”

“…Culture-independent approaches based on clonal analysis of 16S rRNA genes have been also applied to investigations of microbial communities of fish sauces (Chuon et al, 2014;Kim and Park, 2014), but these approaches have limitations in ascertaining microbial community dynamics during fermentation as they tend to be time-consuming, laborious, and hence relatively low throughput. Therefore, highthroughput pyrosequencing has been extensively applied to better understand the microbial community dynamics of fermented foods (Humblot and Guyot, 2009;Jung et al, 2013;Lee et al, 2014a;Roh et al, 2010;Sakamoto et al, 2011).…”

“…Therefore, studies of the microbial dynamics as well as the metabolite changes are indispensable to understand fermentation processes of fish sauces because the metabolites reflect collective phenotypic results of microbial communities and endogenous enzymes 1 H NMR is a very comprehensive, relatively easy, and nondestructive method for the simultaneous analysis of multiple metabolites present in fermented foods. A combination of pyrosequencing and 1 H NMR approach has been suggested to be one of the more powerful ways to better understand the relationships between the microbial community dynamics and metabolite changes during food fermentation (Jeong et al, 2013;Jung et al, 2013Jung et al, , 2014Lee et al, 2014aLee et al, , 2014b. Because fermented salted seafood is usually made by fermentation under highly salted [20-30% (w/w)] conditions, it has been hypothesized that archaea may contribute to salted seafood fermentation (Roh et al, 2010;Tapingkae et al, 2010).…”

“…Because fermented salted seafood is usually made by fermentation under highly salted [20-30% (w/w)] conditions, it has been hypothesized that archaea may contribute to salted seafood fermentation (Roh et al, 2010;Tapingkae et al, 2010). However, recent reports have shown that archaea may not play an important role in salted seafood fermentation Lee et al, 2014a). Therefore, in this study, three sets of MA samples were prepared using anchovies of different sizes and a combination of pyrosequencing and 1 H NMR was applied to investigate bacterial succession and metabolite changes during MA fermentation.…”