Entire Fermentation Period Research Articles

Transcriptomic analysis of the metabolic characteristics of Aspergillus oryzae during the fermentation of doenjang-meju, a traditional Korean fermented soybean brick

To investigate the fermentative traits of Aspergillus oryzae in doenjang-meju, a traditional Korean fermented soybean brick, we prepared doenjang-meju bricks inoculated with both A. oryzae and Bacillus velezensis––recognized as crucial microbes in doenjang-meju fermentation, and then the transcriptomes of A. oryzae were analyzed throughout the entire fermentation period. The transcriptomic analysis of carbohydrate-active enzyme (CAZy) genes revealed that A. oryzae exhibited robust expression of CAZy genes involved in the decomposition of various carbohydrates, particularly cellulose, starch, and hemicellulose, indicating the active breakdown of soybean carbohydrates by A. oryzae during fermentation. Furthermore, KEGG analysis, metabolic pathway reconstruction, and their transcriptomic analysis provided a comprehensive overview of the decomposition patterns of various carbohydrates, lipids, and proteins and the metabolic features of various carbon compounds during fermentation. Additionally, the transcriptomic analysis of biosynthetic gene clusters indicated the potential production of various secondary metabolites by A. oryzae during fermentation. Genes related to carbohydrate and carbon compound metabolisms and secondary metabolite biosynthesis displayed unique and different transcriptional expression patterns depending on the specific gene and fermentation stage. Overall, our findings provide comprehensive insights into the metabolic characteristics of A. oryzae, thus contributing to our understanding of soybean fermentation.

Microbiome dynamics and products profiles of biowaste fermentation under different organic loads and additives.

Biowaste fermentation is a promising technology for low-carbon print bioenergy and biochemical production. Although it is believed that the microbiome determines both the fermentation efficiency and the product profiles of biowastes, the explicit mechanisms of how microbial activity controls fermentation processes remained to be unexplored. The current study investigated the microbiome dynamics and fermentation product profiles of biowaste fermentation under different organic loads (5, 20, and 40g-VS/L) and with additives that potentially modulate the fermentation process via methanogenesis inhibition (2-bromoethanesulfonate) or electron transfer promotion (i.e., reduced iron, magnetite iron, and activated carbon). The overall fermentation products yields were 440, 373 and 208 CH4-eq/g-VS for low-, medium- and high-load fermentation. For low- and medium-load fermentation, volatile fatty acids (VFAs) were first accumulated and were gradually converted to methane. For high-load fermentation, VFAs were the main fermentation products during the entire fermentation period, accounting for 62% of all products. 16S rRNA-based analyses showed that both 2-bromoethanesulfonate addition and increase of organic loads inhibited the activity of methanogens and promoted the activity of distinct VFA-producing bacterial microbiomes. Moreover, the addition of activated carbon promoted the activity of H2-producing Bacteroides, homoacetogenic Eubacteriaceae and methanogenic Methanosarcinaceae, whose activity dynamics during the fermentation led to changes in acetate and methane production. The current results unveiled mechanisms of microbiome activity dynamics shaping the biowaste fermentation product profiles and provided the fundamental basis for the development of microbiome-guided engineering approaches to modulate biowaste fermentation toward high-value product recovery.

Dynamic changes in physicochemical property, biogenic amines content and microbial diversity during the fermentation of Sanchuan ham

Sanchuan ham is appreciated in Yunnan Province, China, for its characteristic flavor and taste, while the microbial community structure and biogenic amines content remain unclear during fermentation processes. In this study, we explored the physicochemical property, biogenic amines concentration and microbial diversity of external and internal Sanchuan ham by high-throughput sequencing during the processing of Sanchuan ham. Results showed that the nitrite remained at a stable level of 0.15 mg/kg which was significantly lower than the national health standard safety level of 20 mg/kg. In addition, compared with fresh hams, the content of total free amino acids in ripe Sanchuan ham has grown 14 folds; sour and bitter were the main tastes of Sanchuan ham. Notably, the concentration of cadaverine was the highest of all biogenic amines during the entire fermentation period. At the bacterial phyla level, Firmicutes and Actinobacteria were the two main phyla, while at the genus level, Staphylococcus was a significant strain throughout the whole fermentation. Moreover, the dry stage has a great impact on the succession change of microbial community structure. Simultaneously, the change trends and composition of bacteria in the interior have slight discrepancies with those of the exterior of Sanchuan ham.

N. Rohova, O. Volodko, Ya. bychkov DEPENDENCE OF LACTOBACILLI ACTIVITY ON THE CONCENTRATION OF SUGAR IN THE SUBSTRATE

The purpose of the article was to extend the shelf life of birch sap and the time of its processing by pre-fermentation of birch sap with pure crops Lactobacillus casei ssp. alactosus. The disadvantage of the existing method of production of birch sap is that the newly collected birch sap must be immediately sent for processing, because short-term storage for no more than 24 hours is allowed only in chilled rooms at a temperature of 0 to 5 0C and a relative humidity of not more than 75 %. In case of violation of these conditions, turbidity of the juice appears, acidity increases and spontaneous fermentation of the juice begins, which has significant flaws. The sugar content in birch sap is relatively low. Since the fluctuations in the sugar content of fresh juice are quite significant, it was necessary to identify the activity of its costs during the fermentation process. Research methodology. The activity of lactobacilli was determined by measuring the loss of dry soluble substances in the juice during fermentation and the accumulation of titrated acids in terms of lactic acid. Results. Fluctuations in sugars depending on weather conditions and place of cultivation range from 0.5 to 0.9 %. The final product of sugar fermentation with lactobacilli, as already noted, is mainly lactic acid and other substances (acetic acid, ethyl alcohol, carbon dioxide, dextrin, mannitol) in small quantities. The term fermentation of birch sap to the desired lactic acid content can be adjusted by adding a certain amount of sugar to it. According to the derived regression equations, it is possible to predict on which day and at what concentration in the juice the desired acidity will be. The concentration of titrated acids in terms of lactic acid changed during the entire fermentation period, which occurred in rectilinear dependence, which is confirmed by the correlation coefficients Conclusions. To activate lactic fermentation with a small amount of sugar, it should be added to freshly harvested birch sap.

Comparative evaluation of the effects of natural and artificial inoculation on soybean paste fermentation

Soybean pastes fermented with natural (NIS) and artificial (AIS) inoculation were prepared to evaluate their fermentation characteristics, flavor compounds and microbial community compositions across an entire fermentation period. The results showed that the initial concentrations of free amino acids and aroma compounds were higher in NIS than in AIS, whereas it was opposite at the end of fermentation. A larger variation of flavor compounds was observed in AIS, which was associated with higher level of microbial metabolism during AIS fermentation. Penicillium and Tetragenococcus were the dominant microbial genera in NIS, while Aspergillus and Pediococcus were predominant in AIS. Correlation analysis of flavor compounds and microbial community dynamics during NIS and AIS fermentation revealed the specific role of microbial taxa in metabolite transformations. Pediococcus acidilactici could be the key microorganism strongly associated with 23 flavor compounds during AIS fermentation. Further, Aspergillus oryzae and Pediococcus acidilactici were primarily linked to amino acid metabolism in AIS, whereas Penicillium and Yaniella were found associated with aroma compounds, Tetragenococcus_sp_JNURIC_D6 and Candida solani with that of organic acids in NIS. These findings provide substantial data on the development of flavor-enhancing fermentation starter culture and the better control of flavor ripening in soybean paste production.

Analysis of microbial community and the characterization of Aspergillus flavus in Liuyang Douchi during fermentation

Liuyang Douchi is a kind of traditional fermented Aspergillus-type Douchi in China for excellent favor. However, studies on the microbial diversity and the characterization of predominate fungi of Liuyang Douchi are few. In present study, the Illumina HiSeq sequencing was performed to reveal the fluctuation characteristics of microbial diversity during fermentation. Results showed that Staphylococcus (33.86%), Staphylococcaceae_unclassified (27.39%) and Pediococcus (8.80%) were the dominated bacteria, while Petromyces (74.57%), Rhizopus (10.93%) and Penicillium (2.68%) were the most predominant fungi during entire fermentation period. Intriguingly, Petromyces was negatively correlated with Alternaria, Saccharomyces and Saccharomycetales_unclassified. Further, four non-aflatoxigenic Aspergillus flavus strains were first identified and isolated from Liuyang Douchi according to phylogenetic and macroscopic characteristics. These four Aspergillus flavus displayed high cellulase and protease activities, but weak lipase activity. This study could contribute to the quality control of Liuyang Douchi by providing an overview of the microbial diversity.

Zinc ion addition to grain media enhanced hispidin production during solid-state fermentation of Phellinus linteus

Hispidin is a secondary metabolite with pharmacological properties that is produced by the medicinal mushroom Phellinus linteus. In this study, we evaluated the effect of metal ion addition to grain media while determining the optimal illumination and temperature conditions for hispidin production in P. linteus 03 using solid-state fermentation. Six metal ions were added to these media and P. linteus 03 grown in these media were for hispidin production under optimal incubation temperature and illumination conditions. The highest yield and specific productivity of hispidin, and total hispidin content were achieved at 25 °C in a dark environment which was maintained throughout the entire fermentation period for brown rice and pearl barley media. Addition of Zn2+ ions to brown rice medium resulted in the highest yield and specific productivity of hispidin and total hispidin content at 6 weeks of fermentation; these were 2.53-, 2.62-, and 2.43-fold, respectively higher than those observed in the control. This study shows that hispidin production by P. linteus 03 can be enhanced by the addition of Zn2+ ions to the grain media.

The succession and correlation of the bacterial community and flavour characteristics of Harbin dry sausages during fermentation

This study was to investigate the succession of the bacterial community in Harbin dry sausages during fermentation and its correlation to the sausage flavour. The results showed that Staphylococcus count increased but the moisture content and water activity decreased (P < 0.05). The lactic acid bacteria count first increased and then decreased, while the pH showed an opposite trend during a twelve-day fermentation (P < 0.05). According to a single molecule real time sequencing analysis, Lactobacillus sakei and Staphylococcus xylosus were the predominant bacterial species over the entire fermentation period. A total of 79 volatile compounds were detected using the headspace solid phase microextraction gas chromatography-mass spectrometry. Furthermore, the correlation between the core bacteria (top 30) and the major volatile compounds was explored, which highlighted that three bacterial species (Lb. sakei, S. xylosus and Weissella hellenica) were significantly correlated with the major volatile compounds, such as 2,3-butanediol, ethanol, 3-hydroxy-2-butanone, ethyl hexanoate and ethyl lactate. The results may provide a theoretical basis for improving the flavour and overall quality of dry sausage.

Identification of biogenic amine-producing microbes during fermentation of ganjang, a Korean traditional soy sauce, through metagenomic and metatranscriptomic analyses

Microbes responsible for producing biogenic amines (BAs) during fermentation of ganjang, a Korean traditional soy sauce, were investigated through metagenomic and metatranscriptomic analyses. BA analysis revealed that cadaverine, putrescine, tyramine, and histamine were generated during ganjang fermentation and BA-producing decarboxylase sequences were searched from metagenomic contigs through BlastP and sequence similarity network analyses. A total of 16 putative BA-producing decarboxylase sequences, including five ornithine decarboxylases (ODC), one lysine decarboxylase (LDC), one histidine decarboxylase (HDC), and nine tyrosine decarboxylases (TDC) were identified and phylogenetically classified. BA-producing gene and expression analysis suggested that cadaverine and histamine might only be produced by the LDC gene of Staphylococcus showing relatively high expression levels and the HDC gene of Tetragenococcus showing very low expression levels, respectively, during the middle fermentation periods. Additionally, putrescine and tyramine might be produced by the ODC and TDC genes, respectively, by various microbes during the entire fermentation period. The analyses also suggested that the ODC genes of Bacillus and Halomonas, expressed at a low level, might be responsible for producing putrescine during early fermentation, while after 60 days the ODC gene of Lactobacillus, expressed at a comparatively high level, might be dominantly responsible for producing putrescine. Additionally, the TDC genes of Bacillus, Enterococcus, and Virgibacillus might be responsible for producing tyramine at 20 and 40 days of fermentation, while after 60 days the TDC gene of Tetragenococcus, which was highly expressed at this time point, along with Virgibacillus and Enterococcus, might be majorly responsible for producing tyramine.

Application of Stable Isotope Tracing to Elucidate Metabolic Dynamics During Yarrowia lipolytica α-Ionone Fermentation.

SummaryTargeted metabolite analysis in combination with 13C-tracing is a convenient strategy to determine pathway activity in biological systems; however, metabolite analysis is limited by challenges in separating and detecting pathway intermediates with current chromatographic methods. Here, a hydrophilic interaction chromatography tandem mass spectrometry approach was developed for improved metabolite separation, isotopologue analysis, and quantification. The physiological responses of a Yarrowia lipolytica strain engineered to produce ∼400 mg/L α-ionone and temporal changes in metabolism were quantified (e.g., mevalonate secretion, then uptake) indicating bottleneck shifts in the engineered pathway over the course of fermentation. Dynamic labeling results indicated limited tricarboxylic acid cycle label incorporation and, combined with a measurable ATP shortage during the high ionone production phase, suggested that electron transport and oxidative phosphorylation may limit energy supply and strain performance. The results provide insights into terpenoid pathway metabolic dynamics of non-model yeasts and offer guidelines for sensor development and modular engineering.

Оптимизация процесса получения нового биоконсерванта для силосования многолетних трав

All-Russian Research Institute of Reclaimed Lands has developed and patented a method for producing a biological preservative for ensiling perennial grasses, which is based on a cascade process for the fermentation and extraction of raw materials (peat and bird droppings). The result is a liquid biological product with a high content of beneficial lactic microflora, nutrients and biologically active substances. One of the advantages of the developed process is the possibility of modification and influence on the final result. The goal of the research outlined in this article was to compare two ways to obtain a bio-preservative (basic and new) and to evaluate the feasibility of using a new multicomponent stimulator. The basic method includes the introduction of bakery production waste as a stimulant and the use of a solution of potassium phosphate as the extractant. The new method is characterized in that a multi-component additive was used as a biological stimulant, including bakery production waste, hardwood ash, ascorbic acid and potassium phosphate. The acetic acid solution was used as an extractant. During the implementation of the processes, the pH value, the total microbial contamination, the activity of the enzymes of the cellulase and invertase. A multicomponent stimulator provided elevated pH values during the entire fermentation period (on average by 22% relative to the base method), which indicated the activation of the microbial community (up to nx109) and active transformation of the feedstock. He was already active in the early stages of fermentation (the invertase-cellulase ratio by the new technology was 1.4 versus 0.8 by the base technology). The pH of biological preservatives changed depending on the extractant: alkaline (6.5) or acidic (4.9). The active reaction of the extractant medium affected the total microbial contamination. In the variant with the basic alkaline extractant, there was a rapid growth of microflora (nx1011). Acidic extractant inhibited the development of many types of microorganisms (nx1010), but it is he who can give priority to lactic acid microorganisms, for which the acidity of the medium is not a limiting factor.

Dynamic evaluation of the nutritional composition of homemade koumiss from Inner Mongolia during the fermentation process

Koumiss plays an important role in income generation for herdsmen and the daily nutritional intake of local people. In this study, the pH, protein, fat, lactose, lactic acid, amino acid, and vitamin content of koumiss were investigated during the entire fermentation period. The results showed that the protein content of fresh mares’ milk and koumiss ranged from 1.86 ± 0.07% to 2.22 ± 0.08%; fat content ranged from 0.74 ± 0.16% to 1.480 ± 0.08%; VB1 concentration ranged from 1.48 ± 0.12 to 4.86 ± 0.42 µg/100 g; VB2 concentration ranged from 2.48 ± 0.12 µg/100 g to 4.86 ± 0.32 µg/100 g; and VE concentration ranged from 99.90 ± 0.05 to 44.63 ± 0.63 µg/100 g. There were significant differences between fresh mares’ milk and koumiss in relation to VE content. The content of 17 amino acids ranged from 2.40 ± 0.11 µg/100 g (for MET) to 39.64 ± 0.01 µg/100 g (for GLU). Fresh mares’ milk and aged koumiss had high nutritional value; however, unripe koumiss (i.e., with a shorter fermentation time) had low nutritional value. Based on the data from this study, an optimized manufacture process for koumiss is proposed. Practical applications The dynamic changes of chemical and nutritional composition of koumiss were evaluated in this present paper. The nutrient content of koumiss is the highest at the point of 12 hr fermentation. The optimized manufacture process for koumiss is proposed based on the result of this study. This paper will provide the basic information for koumiss industrial application.

Efficient production of ε-poly-l-lysine from glucose by two-stage fermentation using pH shock strategy

Abstract In this study, a pH shock strategy was employed to enhance e-poly- l -lysine (e-PL) production from glucose. In the conventional fermentation, in the early stage, only 13% of total e-PL production is achieved in 25% of the entire fermentation period, which severely affected e-PL productivity. To improve the efficiency of e-PL production during fermentation, a novel two-stage fermentation, namely culture and fermentation stages, was proposed on the basis of the analysis of conventional pH shock fermentation. After optimization of parameters such as inoculum growth conditions, initial fermentation pH, and inoculum volume, the e-PL production and productivity achieved using the novel fermentation process in a 5-L fermenter reached 32.22 g/L and 5.86 g/L/day, which were 32.3% and 36.6% higher, respectively, when compared with those obtained in conventional fermentation. Furthermore, evaluation of acid tolerance of mycelia collected from the pH shock fermentation showed that pH shock enhanced e-PL production, which might be related to the acid tolerance of Streptomyces albulus and pH stress (pH 3.0). The results obtained could be useful for large-scale e-PL production and to provide new information on e-PL biosynthesis mechanism.

EFFECT OF ALKYLRESORCINOLS DERIVATIVES ON THE ACTIVITY OF ENZYME PREPARATIONS

Target setting. Rye is known to be a stubborn raw material for the industrial production of alcohol because of alkylresorcinols contained in grain of the said crop these effecting the enzymes of amylase complex in the negative way. Thus it is important to find and scientifically substantiate proper deactivating substances for batches preparation stabilizing enzyme activity without increase of normative consumption rates of enzyme preparations.Actual scientific research and issues analysis. Outer cuticle shell of rye grain contains alkylresorcinols – compounds of resorcine and alkyls of different chain length and odd number of carbon atoms. The presence of alkylresorcinols containing carbon atoms is characteristic for rye only. While grinding grain, the most part of alkylresorcinols remains in bran. When effected by high temperatures alkylresorcinols partly disintegrate, and in alcohol production alkylresorcinols retain their native form and effect the activity of enzyme preparations in negative way.Defining of uninvestigated parts of general matter. Objects of research were: rye, fractions obtained while grinding; batches and wort made of rye mill under the conditions of low temperature digestion with the use of enzyme preparations of alpha- and glucoamylase action and auxiliary cytolytic enzyme preparations, mature mash. To fulfill the research, media were prepared of rye mill and water, rye bran was added as a source of alkylresorcinols; fermentative hydrolysis of starch was fulfilled with the use of «Novozymes» enzyme preparations.The research objective. The aim of the research was to determine the effect of alkylresorcinols derivatives upon the saccharifying ability of wort and to choose substances to neutralize alkylresorcinols.The statement of basic materials. The efficiency of catalytic activity of enzyme preparation during wort fermentation is effected by a number of factors, the index of saccharifying ability of wort being an index of activity of enzyme preparations. The research of deactivating alkylresorcinols derivatives with different substances was fulfilled to confirm or to reject the said assumption. For the research, food grade sodium bicarbonate, ammonia water and sodium hydroxide solution were used as deactivators.Conclusions and proposals. The alkylresorcinols contained in rye effect enzyme preparations of alpha amylitic action in the negative way. The neutralization of alkylresorcinol derivatives promotes retention of enzyme preparations activity along the entire fermentation period of the media. The use of ammonia water and lactic acid at the stage of batches preparation positively influences the fermentation activity of yeast owing to the media enrichment with a source of nitrogen and increases alcohol content in mature mash.

Identification of 4-mercapto-4-methylpentan-2-one as the characteristic aroma of sake made from low-glutelin rice

The grassy characteristic aroma perceived in brewed sake made from low-glutelin rice (Oryza sativa L. Mizuhonoka) was examined by gas chromatography-olfactometry and gas chromatography-mass spectrometry. By comparing the odor properties and Kovats retention indices to those of standard compounds, 4-mercapto-4-methylpentan-2-one (4MMP) was found to contribute to the characteristic aroma. Sake brewing using Mizuhonoka, low-glutelin rice, and Gin-ohmi (a control) revealed that 4MMP concentrations in Mizuhonoka sake samples were higher than those in Gin-ohmi samples over the fermentation period. The concentration in final Mizuhonoka sake was twice that of Gin-ohmi. To investigate the mechanism of 4MMP formation, the putative precursors, 4-S-cycteinyl-4-methylpentan-2-one (cys-4MMP) and 4-S-glutathionyl-4-methylpentan-2-one (glut-4MMP), in sake and its materials (rice and koji) were analyzed by ultra-performance liquid chromatography tandem mass-spectrometry. Cys-4MMP was not detected in all samples, while glut-4MMP was present in sake and its materials. The glut-4MMP concentration in sake was lower than that in Gin-ohmi over nearly the entire fermentation period, suggesting that conversion of the precursors to 4MMP was more effective in the mash of low-glutelin rice Mizuhonoka than in Gin-ohmi. The release of 4MMP during alcoholic fermentation from a model medium containing its precursors was examined. While no 4MMP release was observed in the control (no addition), with the addition of its precursors, the release of 4MMP increased as fermentation progressed. It was suggested that 4MMP was generated from both cys- and glut-4MMP by sake yeast. The perception threshold of 4MMP in sake was determined as 1.2ng/L.

Dynamic analysis of physiological properties of Torulaspora delbrueckii in wine fermentations and its incidence on wine quality.

This work examines the physiology of a new commercial strain of Torulaspora delbrueckii in the production of red wine following different combined fermentation strategies. For a detailed comparison, several yeast metabolites and the strains implantation were measured over the entire fermentation period. In all fermentations in which T. delbrueckii was involved, the ethanol concentration was reduced; some malic acid was consumed; more pyruvic acid was released, and fewer amounts of higher alcohols were produced. The sensorial properties of final wines varied widely, emphasising the structure of wine in sequential fermentations with T. delbrueckii. These wines presented the maximum overall impression and were preferred by tasters. Semi-industrial assays were carried out confirming these differences at a higher scale. No important differences were observed in volatile aroma composition between fermentations. However, differences in mouthfeel properties were observed in semi-industrial fermentations, which were correlated with an increase in the mannoprotein content of red wines fermented sequentially with T. delbrueckii.

Microbial community dynamics during fermentation of doenjang-meju, traditional Korean fermented soybean

Bacterial and fungal community dynamics, along with viable plate counts and water content, were investigated in the exterior and interior regions of doenjang-meju, traditional Korean fermented soybean, during its fermentation process. Measurement of viable cells showed that the meju molding equipment might be an important source of bacterial cells (mostly Bacillus) during doenjang-meju fermentation, whereas fungi might be mostly derived from the fermentation environment including incubation shelves, air, and rice straws. Community analysis using rRNA-targeted pyrosequencing revealed that Bacillus among bacteria and Mucor among fungi were predominant in both the exterior and interior regions of doenjang-meju during the early fermentation period. Bacteria such as Ignatzschineria, Myroides, Enterococcus, Corynebacterium, and Clostridium and fungi such as Geotrichum, Scopulariopsis, Monascus, Fusarium, and eventually Aspergillus were mainly detected as the fermentation progressed. Bacillus, an aerobic bacterial group, was predominant in the exterior regions during the entire fermentation period, while anaerobic, facultative anaerobic, and microaerobic bacteria including Enterococcus, Lactobacillus, Clostridium, Myroides, and Ignatzschineria were much more abundant in the interior regions. Principal component analysis (PCA) also indicated that the bacterial communities in the exterior and interior regions were clearly differentiated, suggesting that aeration might be an important factor in determining the bacterial communities during doenjang-meju fermentation. However, PCA showed that fungal communities were not separated in the exterior and interior regions and Pearson's correlation coefficients showed that the major fungal taxa had significantly positive (Mucor and Geotrichum) or negative (Aspergillus) correlations with the water content during doenjang-meju fermentation, indicating that water content might be a significant factor in determining the fungal communities during doenjang-meju fermentation.

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

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.

혼합 스타터를 이용한 묵은지의 제조 및 발효 특성

To develop a starter culture system for the fermentation of mukeunji, we introduced lactic acid bacteria and yeast isolated from mukeunji into kimchi fermentation as a single or a mixed culture. On evaluating mukeunji flavor, we found that the mixed starter kimchi prepared with two strains, ML17 and MY7, gave the best sensory score. These strains were identified as Lactobacillus (Lb.) curvatus ML17 and Saccharomyces (S.) servazzii MY7 by molecular identification method. The fermentative characteristics of starter kimchi were investigated by measuring changes in the physicochemical and microfloral characteristics during the fermentation. The decrease in pH and increase in acidity in the starter kimchi were faster compared to respective values of control kimchi. There was a gradual decrease in hardness of starter kimchi, which was still slow compared to hardness decrease in control kimchi. Microbial analysis of starter kimchi revealed that Lb. curvatus ML17 and S. servazzii MY7 were the dominant organisms during the entire fermentation period. The lactic acid and citric acid contents of starter kimchi were higher than those of the control kimchi after 90 days of fermentation. By sensory evaluation, the starter kimchi scored higher in appearance, mukeunji flavor, sourness, carbonated flavor, savory taste, texture, and overall acceptability, but lower in off-flavor than the control kimchi.

Effects of temperature on microbial succession and metabolite change during saeu-jeot fermentation

To investigate the effects of temperature on saeu-jeot (shrimp) fermentation, four sets of saeu-jeot samples with approximately 25% (w/v) NaCl were fermented at 10 °C, 15 °C, 20 °C, and 25 °C. The pH values of the 10 °C and 15 °C samples were relatively constant during the entire fermentation period, whereas those of the 20 °C and 25 °C samples gradually decreased after 25 days of fermentation. Quantitative PCR showed that the maximum bacterial abundance was greater in higher temperature samples, and the bacterial abundance in the 10 °C samples steadily decreased during the entire fermentation period. Community analysis using pyrosequencing revealed that the initially dominant Proteobacteria including Pseudoalteromonas, Photobacterium, Vibrio, Aliivibrio, and Enterovibrio were replaced rapidly with Firmicutes such as Psychrobacter, Staphylococcus, Salimicrobium, Alkalibacillus, and Halanaerobium as the fermentation progressed. However, Vibrio, Photobacterium, Aliivibrio, and Enterovibrio, which may include potentially pathogenic strains, remained even after 215 days in the 10 °C samples. Metabolite analysis using 1H NMR showed that amino acid profiles and initial quick increases of glucose and glycerol were similar and independent of bacterial growth in all temperature samples. After 25 days of fermentation, the levels of glucose, glycerol, and trimethylamine N-oxide decreased with the growth of Halanaerobium and the increase of acetate, butyrate, and methylamines in the 20 °C and 25 °C samples although the amino acid concentrations steadily increased until approximately 105 days of fermentation. Statistical triplot analysis showed that the bacterial successions occurred similarly regardless of the fermentation temperature, and Halanaerobium was likely responsible for the production of acetate, butyrate, and methylamines. This study suggests that around 15 °C might be the optimum temperature for the production of safe and tasty saeu-jeot.