Characteristic aroma compounds during the fermentation of Chinese steamed bread fermented with different starters.

The characteristic aroma compounds of Chinese steamed bread (CSB) fermented with different starters were studied using HS-SPME-GC/MS, aroma recombination and omission experiments. The dynamic changes of the microbiota and their function and metabolites during fermentation were analyzed using metagenomics and non-targeted metabolomics. Forty-nine volatile flavor compounds were identified, while 5 characteristic aroma-active compounds were investigated in CSB fermented with commercial dry yeast (AQ-CSB), and 10 were investigated in CSB fermented with traditional starter (NY-CSB). Microbial structure and function analysis showed that Saccharomyces cerevisiae dominated during AQ-CSB fermentation and contributed >95% to its KEGG pathways, while Pediococcus pentosaceus, unclassified Pediococcus, Lactobacillus plantarum, Lactobacillus brevis and unclassified Lactobacillus were predominant in NY-CSB and together had an ~96% contribution to these pathways. NY-CSB showed higher metabolic activity during fermentation, and the characteristic metabolites were mainly involved in carbohydrate, amino acid and lipid metabolism. The characteristic aroma compounds were identified and increased the understanding of the contributions of the microbiota. This may be useful for designing starter cultures that produce CSB with desirable aroma properties.

Microbiota structure of traditional starters from around the Tai-hang mountains and their influence on the fermentation properties, aroma profile and quality of Chinese steamed bread.

BACKGROUND: Steamed bread is a popular staple food in China, and the significant regional differences of the microbiota in traditional starters make the flavor and quality of steamed bread highly variable along with long preparation times. Therefore, analyzing the microbial flora of traditional starters and their influences on the flavor and quality may help to solve the problems mentioned earlier, and it may also be conducive to potentially meet consumer needs and permit industrialization of this traditional fermented food. RESULTS: One hundred and thirty-two fungal and 50 bacterial species were identified in five traditional starters, each with a different dominant genus. The fermentation properties of dough showed that total titratable acid, dough volume and gas production increased and the pH decreased with fermentation time. The traditional starters improved the quality of Chinese steamed bread (CSB) including the crumb structure, specific volume and sensory attributes. Thirty-three aroma compounds with a VIP (variable importance for the projection) > 1 were identified as characteristic aroma compounds. The correlations among the microbiota, aroma and qualities of CSB showed a greater contribution from the bacteria, which was consistent with the predictions of metabolic pathways in the sequenced genomes. CONCLUSION: The quality of CSB fermented with traditional starters was improved induced by their different microbial profiles, and bacteria made a greater contribution than fungus to the aroma and qualities of CSB. © 2023 Society of Chemical Industry.

Three recombinant peroxidases as a degradation agent of aflatoxin M1 applied in milk and beer.

The aim of this work was to estimate the effects of three recombinant peroxidases (rPODs) on the degradation of aflatoxin M1 (AFM1) in a model solution and were applied in milk and beer to study the AFM1 degradation. Besides, the contents of AFM1 in model solution, milk and beer were evaluated, and the kinetic parameters of rPODs were determined (Michaelis-Menten constant - Km and maximal velocity - Vmax). The optimized reaction conditions (The degradation was over 60 %) for these three rPODs in the model solution were, respectively as follows: pH were 9, 9, and 10; hydrogen peroxide concentrations were 60, 50, and 60 mmol/L; at an ionic strength of 75 mmol/L and reaction temperature of 30 °C with 1 mmol/L K+ or 1 mmol/L Na+. These three rPODs (1 U /mL) presented the maximum activity for degradation of AFM1 of 22.4 %, 25.6 %, and 24.3 % in milk, while 14.5 %, 16.9 %, and 18.2 % in beer, respectively. Meanwhile, the survival rate of Hep-G2 cells raised about 1.4 times after treated with peroxidase-generated AFM1 degradation products. Therefore, POD may be a promising alternative to reduce the pollution of AFM1 in model solution, milk, beer, and minimize their impact on the environment in humans.

Exploration of microbial profile of traditional starters and its influence on aroma profile and quality of Chinese steamed bread.

BACKGROUND: Chinese steamed bread (CSB) is a popular staple food in China with traditional ethnic characteristics. CSB with traditional starters has good flavor and texture but is unstable and requires a long preparation time. Therefore, it is necessary to analyze the traditional starters (ST) and their influence on the flavor and quality of steamed bread to meet people's requirements as a staple food. RESULTS: The count of yeast, lactic acid bacteria and total microbial population significantly varied in different traditional starters; Saccharomyces and Lactobacillus were the predominant genera. Among the tested samples, fungi were found in ST from Shijiazhuang (SJ), Handan (HD) and Langfang (LF), while bacteria were found in ST from Tangshan (TS) and SJ at sub-predominant levels. In terms of the bread quality, the highest specific volume and porosity were in XT-CSB (Xingtai); the highest height/diameter ratio was in SJ-CSB; and the highest sensory score was in TS-CSB. A total of 26 aroma compounds (VIP > 1; variable importance for predictive components) were identified to discriminate CSB fermented with different starters, which were separated by stepwise canonical discriminant analysis using two functions. The correlation analysis among microbiota, aroma compounds and bread quality showed a higher contribution of bacteria than of fungi. CONCLUSION: Differences in microbial profiles caused different aroma profiles and quality of CSB; and the CSB fermented with traditional starters were sufficiently separated by stepwise canonical discriminant analysis based on aroma compounds. © 2023 Society of Chemical Industry.

Microbiology, flavor formation, and bioactivity of fermented soybean curd (furu): A review.

Soybeans are an important plant-based food but its beany flavor and anti-nutritional factors limit its consumption. Fermentation is an effective way to improve its flavor and nutrition. Furu is a popular fermented soybean curd and mainly manufactured in Asia, which has been consumed for thousands of years as an appetizer because of its attractive flavors. This review first classifies furu products on the basis of various factors; then, the microorganisms involved in its fermentation and their various functions are discussed. The mechanisms for the formation of aroma and taste compounds during fermentation are also discussed; and the microbial metabolites and their bioactivities are analyzed. Finally, future prospects and challenges are introduced and further research is proposed. This information is needed to protect the regional characteristics of furu and to regulate its consistent quality. The current information suggests that more in vivo experiments and further clinical trials are needed to confirm its safety and the microbial community needs to be optimized and standardized for each type of furu to improve the production process.

The aroma profile and microbiota structure in oil furu, a Chinese fermented soybean curd.

The aroma compounds and the microbial community of oil furu, a specific fermented soybean curd, during fermentation were investigated using HS-SPME-GC/MS and high-throughput sequencing, respectively, and their correlations and the predicted functional roles of the microbiota in oil furu were analyzed. Twenty two volatile flavor compounds (relative odor activity value ≥1) were identified that contributed to the aroma profile, which were mainly associated with the aroma attributes. Lactobacillales, Trichosporon and Mucor racemosus were the predominant genera during pre-fermentation, while Candida and Tetragenococcus were predominant during ripening. Correlation analysis showed significant correlation between the microbiota and aroma profiles, and Candida, Empedobacter, Lactobacillus, Pseudomonas, Stenotrophomonas, Trichosporon and Mucor racemosus were significantly and strongly correlated with the characteristic volatile aroma compounds of oil furu (P < 0.05, r > 0.6). Functional analysis showed that metabolic pathways showed higher activity in oil furu, which mainly included amino acid, lipid and carbohydrate metabolism. The results allowed identification of the important aroma compounds and understanding the contribution of the microbiota, and would be useful for designing starter cultures to produce oil furu with desirable aroma properties and understanding its aroma formation pathways.

The fermentation-time dependent proteolysis profile and peptidomic analysis of fermented soybean curd.

The proteolysis and peptidomic profiles and potential bioactivities of fermented soybean curd (furu) during fermentation were studied. The degree of protein hydrolysis (DH) and peptide content significantly increased with fermentation time (p < 0.05), and reached the highest levels after ripening for 90 days. The variety and abundance of bioactive peptides in furu samples were fermentation-time dependent, and furu ripening for 30 and 90 days showed the highest similarity. An ACE-inhibitor and antioxidant peptides were the two main bioactive peptide components, and their abundance and bioactivities exhibited a significant increase with fermentation and reached the maximum levels at 90 days. All these results indicated that microbial fermentation is an effective way to obtain bioactive peptides with soy-based fermented products, and their effects on health might be explored in future studies. PRACTICAL APPLICATION: This work indicated that microbial fermentation is an effective way to obtain bioactive peptides with soy-based fermented products.

Comparative aroma and taste profiles of oil furu (soybean curd) fermented with different mucor strains.

The effects of different mucor strains (Mucor racemosus, Actinomucor, and Mucor wutungkiao) on aroma and taste profiles based on proteolysis, lipolysis, and their catabolism in oil furu were studied. Gas chromatography-mass spectrometry and relative odor activity were used to monitor the changes of key volatile compounds and the differences in the characteristic aroma contents of oil furu. Using principal component analysis, the different fermentation strains had an effect on aroma profiles. The volatile compounds from metabolism of protein and fatty acid contributed to the aroma of oil furu with different contribution from the different strains, presumably due to their different enzymes. The electronic tongue and free amino acid profiles also showed strain differences of taste. Based on these results, optimization of the amount of each of the different mucor strains during cofermentation might achieve better flavor.

Effects of alkaline pretreatments and acid extraction conditions on the acid-soluble collagen from grass carp (Ctenopharyngodon idella) skin.

This study investigated the effects of alkaline pretreatments and acid extraction conditions on the production of acid-soluble collagen (ASC) from grass carp skin. For alkaline pretreatment, 0.05 and 0.1M NaOH removed non-collagenous proteins without significant loss of ASC at 4, 10, 15 and 20 °C; while 0.2 and 0.5M NaOH caused significant loss of ASC, and 0.5M NaOH caused structural modification of ASC at 15 and 20 °C. For acid extraction at 4, 10, 15 and 20 °C, ASC was partly extracted by 0.1 and 0.2M acetic acid, while 0.5 and 1.0M acetic acid resulted in almost complete extraction. The processing conditions involving 0.05-0.1M NaOH for pretreatment, 0.5M acetic acid for extraction and 4-20 °C for both pretreatment and extraction, produced ASC with the structural integrity being well maintained and hence were recommended to prepare ASC from grass carp skin in practical application.