The combination of high-throughput sequencing and LC-MS/MS reveals the mechanism of Staphylococcus inoculation on bacterial community succession and taste development during the processing of dry-cured bacon

Flavor effect, application status, and research trend of umami peptides based on microbial fermentation in food

Umami peptides are important non-volatile compounds produced by protein degradation, contributing to food umami flavor and enhancing product quality. Microbial fermentation promotes the production of taste peptides, including umami peptides, which act as key flavor substances and precursors. Microbial-derived umami peptides are cost-effective, easy to produce, and a major source of umami peptide production. Although microbial fermentation of umami peptides has been extensively studied in preparation, screening, and evaluation, a systematic review of microbial fermentation is still lacking. Therefore, this paper aims to address the following aspects: (1) umami peptide taste characteristics, influencing factors, and preparation methods; (2) microbial sources of umami peptides; (3) the current application status of microbial fermentation-derived umami peptides in various foods; and (4) future directions for microbial fermentation of umami peptides. Consequently, this literature review seeks to offer insights for advancing microbial fermentation in umami peptide production.

LC-MS/MS-based metabolomics and multivariate statistical analysis reveal the mechanism of yeast extracellular proteases on myofibrillar protein degradation, metabolite development and sensory characteristics improvement

Yeast extracellular proteases play a key role in developing the taste of dry-cured ham, whereas the mechanism of yeast proteases on taste formation of dry-cured ham is not fully studied. The proteases characteristics of yeast isolated form Jinhua ham, hydrolysis capacities for myofibrillar proteins (MP), free amino acid contents, metabolite compositions, taste parameters and the relationship between metabolites and taste parameters were investigated to reveal the mechanism of Rhodotorula mucilaginosa AUMC 9298 (RM) and Candida parapsilosis d70a (CP) proteases on MP hydrolysis and taste development of dry-cured ham. The proteases of RM and CP showed high hydrolysis activities at the conditions of pH 5.0-8.0 and 30-50 °C. The proteases of RM showed higher capability to degrade myosin compared with CP proteases and Pichia kudriavzevii XS-5 (PK) proteases. The total free amino acid contents increased from 18.44 mg/100 mL in PK to 33.91 mg/100 mL in RM and 25.28 mg/100 mL in CP after 4 h hydrolysis of MP. Thirty-two metabolites were identified by LC-MS/MS, and peptides and amino acid derivatives were the key components of MP hydrolysates. The scores of umami, richness and aftertaste showed the largest values in RM among these groups. PLS-DA and correlation demonstrated that aspartic acid, N-Methyl-aspartic acid, Glu-Glu, γ-Glu-Cys, glutamic acid, γ-Glu-Glu and γ-Glu-Gln were positive correlation with the improvement of umami, richness and aftertaste.

TMT-labelled quantitative proteomics reveals the mechanism of Rhodotorula mucilaginosa on proteolysis of dry-cured ham: Structural protein degradation, amino acid release and taste improvement

To investigate the mechanism of Rhodotorula mucilaginosa on structural protein degradation and taste development of Jinhua ham, the effects of Rhodotorula mucilaginosa and Pichia kudriavzevii on proteolytic enzyme activities, surface hydrophobicity, myofibril microstructure, protein degradation, free amino acids and sensory attributes were investigated during the dry-ripening of Jinhua ham. The inoculation of Rhodotorula mucilaginosa EIODSF019 (RE) and Rhodotorula mucilaginosa XZY63-3 (RX) consistently exhibited higher proteolytic enzyme activities compared with Pichia kudriavzevii XS-5 (PK). The decrease of α-helix exposing more internal hydrophobic groups of myofibrillar proteins, contributed to higher surface hydrophobicity of RE compared with PK and RX. RE showed the highest proteolysis index among all groups, which could be attributed to more degradation of myosin, actin and troponin; the changes were confirmed by the intense breakdown of myofibrils observed by atomic force microscopy and transmission electron microscopy. 36 down-regulated proteins mainly derived from myofibrils and catalysis-related enzymes were identified in RE by TMT-labeled quantitative proteomics analysis. The degradation of myosin, actin and troponin showed the most intense response to the accumulation of glutamic acid, lysine and alanine. Partial least square regression analysis and correlation analysis revealed that the breakdown of MYH14, MYH3, TNNI1 and TNNTI was highly correlated with improvement of umami, richness and aftertaste.

Comparative analysis of lipolytic enzymes involved in the surface fermentation of dried katsuobushi by xerophilic molds

BACKGROUND

Fermented katsuobushi, a traditional Japanese seasoning, is produced from skipjack tuna through smoking, drying and fermentation by xerophilic Aspergillus molds, primarily Aspergillus chevalieri and Aspergillus pseudoglaucus. In this study, we characterized lipolytic enzymes (cLip_1 to cLip_5 and pLip_1 to pLip_3) to clarify their roles in lipid hydrolysis during katsuobushi production under low water activity.

RESULTS

The enzymes showed significant diversity in their activity, stability and substrate specificity, and in the hydrolysis profiles of their reactions with fish oil. Phylogenetic analyses revealed that cLip_5 showed a high identity with pLip_2 (94%) and these enzymes formed a phylogenetic cluster with filamentous fungal lipases. Purified recombinant enzymes (rcLip_1, rcLip_2, rcLip_4 and rcLip_5) and wild-type enzymes (cLip_3 and pLip_3) showed varying substrate preferences toward p-nitrophenyl esters. The addition of glycerol to reduce the water activity in the reaction mixture led to increased activities of rcLip_1 and rcLip_4, but it did not affect the activity of the other three enzymes. Among the tested six enzymes, cLip_5 showed the highest hydrolytic activity toward fish oil. The cLip_5 and pLip_2 gene transcript levels were moderately high in strains MK86 and MK88, respectively.

CONCLUSION

cLip_5 and its homolog pLip_2 were identified as the most promising enzymes for katsuobushi fermentation, because of their high hydrolytic activities toward fish oil and adaptability to low water activity conditions. These findings support the selection of optimal Aspergillus strains as starter cultures to potentially shorten the fermentation time and improve the quality and shelf life of katsuobushi. © 2025 Society of Chemical Industry.

Insights into the flavor contribution, mechanisms of action, and future trends of coagulase-negative staphylococci in fermented meat products: A review

During fermentation, meat is pre-treated and cured to cultivate a diverse microflora, resulting in fermented meat products with distinctive flavors. Coagulase-negative staphylococcus holds a crucial role in all fermented meat products, contributing to the breakdown of proteins, carbohydrates, and fats, and the creation of flavor compounds. Fermentation technology has important research value and significance in fermented meat products. The optimization and improvement of flavor by CNS can be achieved by regulating the fermentation environment, initial microflora and processing conditions. The review explores the ways in which coagulase-negative staphylococci contribute to the flavors in fermented meat products. The mechanism of flavor substance formation and means of regulation in coagulase-negative staphylococci were also investigated. The review concludes by summarizing future development trends and drawing conclusions.

Astral-based DIA proteomics explored the flavor enhancement mechanism of Chinese traditional smoked bacon by staphylococcal co-fermentation

The proteolysis pattern during mixed fermentation of Staphylococcus cohnii WX-M8 and S. saprophyticus MY-A10 on Chinese bacon was still unknown. In this study, the changing laws of protein degradation products during staphylococcal mixed fermentation were analyzed, followed by an investigation of endogenous enzymes and cellular components, and finally an examination of flavor profiles. Results indicated that mixed fermentation improved protein degradation and promoted the production of peptides and free amino acids (FAAs). Proteolysis of S. saprophyticus MY-A10 was non-specific, and it promoted protein degradation by cooperating with cathepsin L1. S. cohnii WX-M8 was specific and acted mainly with calpain-3 in the thin filament. The fulfillment of S. cohnii WX-M8 function was enhanced in the presence of S. saprophyticus MY-A10. Mixed fermentation showed synergism with endogenous peptidases in degrading peptides to small-molecule peptides or FAAs and complementarity with endogenous dehydrogenases in converting FAAs to volatile organic compounds (VOCs).

Influence of sonication-assisted fermentation on the physicochemical features and antioxidant activities of yogurts fortified by polyphenol-rich pineapple peel powder with varied chemical profiling

This study investigated the effects of pineapple peel powder with varied chemical profiles and sonication-assisted polyphenol biotransformation during fermentation on the quality characteristics of yogurt products. It aimed at exploring the feasibility of sonication-assisted fermentation to enhance the physicochemical properties, control post-acidification, and improve antioxidant activities in yogurts fortified with polyphenol-rich pineapple peel powder. Targeted analysis showed that polyphenol-rich pineapple dietary fiber obtained by ultrasonication-assisted extraction (NPFU) exhibited the slowest rates of acidification, highest antioxidant capacity, and lowest degree of whey separation at 21.67 %. Sonication pretreatments significantly increased transformation of free phenolic acids derived from pineapple peel fiber during fermentation, particularly increasing the accumulation of ferulic acid, caffeic acid and 5-hydroxyflavone, revealing the positive effects of sonication-mediated fermentation in promoting the hydrolysis of conjugated phenolics into free fractions. Yogurts fortified with pineapple peel fiber displayed significantly higher antioxidant activities (p < 0.05) compared to those with pineapple peel whole powder, corresponding with the increased free phenolics. Non-targeted metabolomics analysis was employed to explore the mechanisms underlying the alleviated post-acidification by sonication-assisted fermentation during storage. Metabolomic profiling revealed that the bioactive components from pineapple peel extract significantly influenced the metabolism pathways of lactic acid bacteria particularly involving galactose metabolism, glycerophospholipid metabolism, closely associated with the acid production of the strains and the regulation of the post-acidification rates of yogurt during storage. These results confirmed the potential of ultrasound-assisted fermentation combined with the addition of pineapple dietary fiber to enhance yogurt quality, providing an innovative tool to develop future yogurt products with high marketability.

New insights into the dominance of mixed fermentation of Staphylococcus cohnii and Staphylococcus saprophyticus in Chinese bacon: Complete genomic and comparative genomic perspectives

Previous studies have demonstrated that Staphylococcus cohnii WX_M8 and S. saprophyticus MY_A10 significantly enhanced the flavor of Chinese bacon in a mixed fermentation. However, due to the complexity of the processing, the contribution of the bacteria is deceptive when investigating only the phenotypic changes at the time of fermentation. In order to clarify the metabolic mechanisms of mixed fermentation, a technological characterization, whole genome and comparative genomics analysis, and metabolites were approached in this study. Results showed that differences in tolerance characteristics existed between WX_M8 and MY_A10. And the genomes of both the two strains consisted of one chromosome and four circular plasmids. Their genome sizes were 2.74 Mp and 2.62 Mp, the GC contents were 32.45% and 33.18%, and the predicted coding genes (CDS) were 2564 and 2541, respectively. Based on the annotation of gene functions and assessment of metabolic pathways in the KEGG database, WX_M8 and MY_A10 strains were found to harbor complete protein degradation and amino acid metabolic pathways, pyruvate and butanol metabolic pathways, and isoleucine metabolic pathways, and their diverse enzyme-encoding genes superimposed the metabolic functions, whereas the alcohol dehydrogenase genes, adh and frmA, achieved complementary functions in the production of esters. Comparative genomics analysis revealed a diversity of encoding genes of aminotransferases and a greater metabolism for sulfur-containing amino acids, aromatic amino acids, and branched-chain amino acids in the mixed fermentation of strains WX_M8 and MY_A10. Metabolites analysis showed that MY_A10 focused on the production of soluble peptides and free amino acids (FAAs), while WX_M8 focused on volatile organic compounds (VOCs), resulting in a significant enhancement of the flavor of Chinese bacon when the two were mixed fermented. This result may provide direction for strains WX_M8 and MY_A10 to be used as starter cultures and targeted to regulate flavor.

Impacts of Aspergillus oryzae 3.042 on the flavor formation pathway in Cantonese soy sauce koji

To investigate the mechanism of flavor formation during the traditional preparation Cantonese soy sauce koji (TP), the changes of microorganisms, physicochemical properties, and flavor compounds in TP were comprehensively and dynamically monitored by absolute quantitative methods. Results demonstrated that inoculating Aspergillus oryzae 3.042 in TP was crucial role in enhancing enzyme activity properties. Absolute quantification of flavor combined with multivariate statistical analysis yielded 5 organic acids, 15 amino acids, and 2 volatiles as significantly different flavors of TP. Amplicon sequencing and RT-qPCR revealed that the dominant genera were Staphylococcus, Weissella, Enterobacter, Lactic streptococci, Lactobacillus, and Aspergillus, which exhibited a increasing trend in TP. Correlation analysis exhibited that Staphylococcus and Aspergillus were the pivotal genera contributing to the enzyme activities and flavor of TP. The flavor formation network involved lipid and protein degradation, carbohydrate metabolism and other pathways. Simultaneously, TP can appropriately increase the fermentation time to improve product quality.

Fungal-Bacterial Mutualism: Species and Strain-Dependent Simultaneous Modulation of Branched-Chain Esters and Indole Derivatives in Fermented Sausages through Metabolite Cross-Feeding

The precise impact of species and strain diversity on fungal-bacterial interactions and the overall community functioning has remained unclear. First, our study revealed how Debaryomyces hansenii influences diverse bacteria to accumulate key metabolites in a simulated fermented food system. For flavor, D. hansenii promoted the accumulation of branched-chain esters in Staphylococcus xylosus by promoting growth and facilitating the precursor branched-chain acids transformations but hindered the accumulation of Staphylococcus equorum. Furthermore, fungal-bacterial interactions displayed diversity among S. equorum strains. For bioactive compounds, species and strain diversity of lactic acid bacteria (LAB) also influences the production of indole derivatives. Then, we investigated specific metabolic exchanges under reciprocal interaction. Amino acids, rather than vitamins, were identified as the primary drivers of the bacterial growth promotion. Moreover, precursor transformations by D. hansenii played a significant role in branched-chain esters production. Finally, a synthetic community capable of producing high concentrations of branched-chain esters and indole derivatives was successfully constructed. These results provide valuable insights into understanding and designing synthetic communities for fermented sausages.

Generation of key aroma compounds in fat and lean portions of non-smoked bacon induced via lipid pyrolysis reaction

This study explored the evolution of key aroma compounds and their lipid precursors in the lean (LN) and fat (FT) portions of non-smoked bacon during hot air drying. The results showed that the LN portion contained most of the aroma compounds in the bacon (>88%). The volatile content of the FT portion increased as the drying time increased, whereas that of the LN portion reached a maximum within 24 h and then decreased. Based on the highest volatile contents (4889.48 ± 202.06 µg/kg) and sensory scores, 24 h was considered the optimal drying time. For key aroma compounds, hexanal and 2,3-octanedione were derived from free fatty acids and polar lipids. Notably, 1-octen-3-ol was generated only from polar lipids in the FT and LN portions. The 2-undecenal and (E, E)-2,4-decadienal were produced by the oxidation of neutral lipids in the FT portion. Dihydro-5-pentyl-2(3H)-furanone was derived from polar lipids in the LN portion. Altogether, these findings provide theoretical insights into improving the aroma of bacon by optimizing raw material selection and processing methods.

TMT-labeled quantitative proteomic reveals the mechanism of proteolysis and taste improvement of dry-cured bacon with Staphylococcus co-inoculation

To understand the mechanism of co-inoculation of Staphylococcus xylosus and Staphylococcus vitulinus (SX & SV) on structural protein degradation and taste enhancement of dry-cured bacon, protease activities, protein degradation, surface morphology of proteins and taste parameters of dry-cured bacon with Staphylococcus inoculation were investigated. The dry-cured bacon with co-inoculation of Staphylococcus xylosus and Staphylococcus vitulinus showed the best taste attributes. High residual activities in cathepsin B + L (more than 1.6-fold) and alanyl aminopeptidase (more than 1.4-fold) accelerated structural protein degradation in SX & SV. 32 down-regulated proteins were identified in SX & SV by TMT-labeled quantitative proteomic compared with control group; myosin and actin showed the most intense response to the accumulation of sweet and umami amino acids, and atomic force microscopy confirmed structural proteins breakdown by morphological changes. The accumulation of glutamic acid, alanine and lysine was mainly responsible for taste improvement of dry-cured bacon with Staphylococcus co-inoculation.

Staphylococcus inoculation enhances the sensorial attributes of Chinese bacon by coordinating the composition of flavor compounds through amino acid metabolism

In this study, we aimed to uncover the potential underlying mechanisms of the flavor modulation of Chinese bacon by Staphylococcus. To that end, taste-enhancing S. cohnii WX-M8 and S. saprophyticus MY-A10 screened from Chinese bacon were used to investigate the effects of their individual and mixed fermentations and their synergistic fermentation with Lactobacillus plantarum BL-1 on the sensorial attributes, physicochemical properties, microbial diversity, and volatile compounds (VOCs) of Chinese bacon. Our results revealed that S. cohnii WX-M8 and S. saprophyticus MY-A10 significantly increased a* (redness) and Aw and reduced thiobarbituric acid reactive substances (TBARS) when fermented in a mixture. Moreover, they promoted the formation of esters, aldehydes (especially straight-chain aldehydes), and phenolic compounds through pathways related to amino acid metabolism, enhancing sensorial attributes. While synergistic fermentation with L. plantarum BL-1 resulted in an improved a* (redness) of Chinese bacon, and the increased microbial metabolism of the carbohydrate and lipid metabolic pathways, the increase in TBARS and the higher content of acidic volatiles, led to a change in the composition of the flavor substances. The advantage of co-fermentation of Staphylococci in sensory attributes can be attributed to their capability to metabolize amino acids and associates. These findings provide insights into the role of Staphylococcus as a starter in regulating bacon flavor.

Effects of lactic acid bacteria-derived fermented feed on the taste and quality of duck meat

The present study aimed to examine the impact of lactic acid bacteria- fermented feed (FF) on the taste and quality of duck meat, in addition to elucidating the potential metabolomic mechanism at play. The findings revealed that ducks fed with FF exhibited elevated pH levels and reduced cooking loss in their meat when compared to the control group. In addition, the sensory evaluation and e-tongue analysis revealed that the tenderness, juiciness, umami, richness, saltiness, and sweetness of duck meat were all enhanced by feeding FF. Moreover, an examination of the metabolome using 1H nuclear magnetic resonance (1H NMR) identified the principal differential metabolites that exhibited a correlation with taste, which included 2-aminoadipate, glucose, glycine, N-acetylcysteine, niacinamide, proline, and threonine. Furthermore, the differential metabolites that exhibited the greatest enrichment in duck meat could be primarily traced to glutathione metabolism, glycine, serine and threonine metabolism, taurine and hypotaurine metabolism. The potential factors contributing to the effect of FF and basic commercial duck feed (CF) were found to be primarily regulated via the aforementioned metabolic pathways. The study, therefore, offers a viable approach for enhancing the taste and quality of duck meat.