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In this study, six lipase-producing strains from food sources were screened for their ability to produce lipase. Among them, Staphylococcus epidermidis N30 and Yarrowia lipolytica C11 demonstrated high enzyme activities of 1.07 and 0.84 U/mL, respectively. They had the following enzymatic properties: optimum reaction temperature of 50 ℃ and pH of 8.0. The optimum substrate for S. epidermidis N30 was C4 ester, while that for Y. lipolytica C11 was C8 ester. The inoculation of sour meat with S. epidermidis N30 or Y. lipolytica C11 effectively enhanced the production of flavor substances, especially ethyl butyrate, ethyl caproate, ethyl caprylate, ethyl caprate, nonanal and 1-octen-3-ol, thus promoting the production of fruity, floral, wine-like, mushroom-like and fatty aromas in sour meat.

Strong-flavor Daqu, as a fermentation agent, plays a significant role in shaping the quality of strong-flavor baijius, and fungal species in Daqu are important factors affecting the quality of Daqu. Therefore, we selected strong-flavor Daqu from seven different origins to study the fungal composition and the effects of the fungal composition on the physicochemical properties and volatile organic compounds (VOCs). It was found that the fungal composition influences the physicochemical properties of Daqu. Specifically, there was a positive link between Rhizomucor, Rhizopus, Thermomyces, and liquefying activity and a positive correlation between Aspergillus and fermenting activity. Furthermore, the relationships between esterifying activity and Thermomyces, Rhizomucor, Aspergillus, Pichia, and Saccharomycopsis were found to be positive. The VOCs in Daqu were affected by Aspergillus, Issatchenkia, Pichia, and Thermoascus. Issatchenkia was significantly positively correlated with benzeneethanol as well as Aspergillus and pentadecanoic acid ethyl ester, ethyl myristate. Pichia and Thermoascus were significantly negatively correlated with benzaldehyde and 2-furaldehyde. This study deepens our understanding of the relationship between VOCs, the physicochemical properties with microbial communities, and reference significance for the production of better-quality strong-flavor Daqu. [ABSTRACT FROM AUTHOR]

Cider flavor has a very important impact on the quality. Solid-phase microextraction-gas chromatography–mass spectrometry (SPME-GC-MS) combined with gas chromatography–ion mobility spectrometry (GC-IMS) tested different kinds of non-Saccharomyces yeasts and Saccharomyces cerevisiae (S. cerevisiae) co-inoculated for the fermentation of cider to determine differences in aroma material, and the determination of odor activity value (OAV) is applied less frequently in research. Through Rhodotorula mucilaginosa, Debaryomyces hansenii, Zygosaccharomyces bailii, and Kluyveromyces Marxianus, four different strains of non-Saccharomyces yeast fermented cider, and it was found that, in both the chemical composition and flavor of material things, compared with monoculture-fermented cider using S. cerevisiae, all differences were significant. Co-inoculated fermentation significantly improved the flavor and taste of cider. As in the volatile compounds of OVA > 1, octanoic acid (Sc 633.88 μg/L, co-inoculation fermented group 955.49 μg/L) provides vegetable cheese fragrance and decanoic acid, ethyl ester (Sc 683.19 μg/L, co-inoculation fermented group 694.98 μg/L) a creamy fruity fragrance, etc., and the average content increased after co-inoculated fermentation. Phenylethyl alcohol, which can produce a rose scent, was relatively abundant in cider samples and varied greatly among the groups. Moreover, the contents of ethyl lactate and 1-butanol in the Sc+Rm (ciders fermented by S. cerevisiae and R. mucilaginosa) were the highest of all of the cider samples. Different types of non-Saccharomyces yeast produced cider with different flavor characteristics. This study demonstrates that different species of non-Saccharomyces yeast do have an important impact on the characteristics of cider and that co-inoculation with non-Saccharomyces yeast and S. cerevisiae for cider fermentation may be a strategy to improve the flavor of cider. [ABSTRACT FROM AUTHOR]

In this study, three Lactiplantibacillus plantarum, namely 3-14-LJ, M22, and MB1, with high acetate esterase activity, acid, salt, and high-temperature tolerance were selected from 708 strains isolated from fermented food. Then, L. plantarum strains MB1, M22, and 3-14-LJ were inoculated at 107 CFU/mL in the model and 107 CFU/g in actual Suanzhayu systems, and the effects during fermentation on the physicochemical properties, amino acid, and volatile substance were investigated. The results showed that the inoculated group had a faster pH decrease, lower protein content, higher TCA-soluble peptides, and total amino acid contents than the control group in both systems (p < 0.05). Inoculation was also found to increase the production of volatile compounds, particularly esters, improve the sour taste, and decrease the bitterness of the product (p < 0.05). L. plantarum M22 was more effective than the other two strains in stimulating the production of isoamyl acetate, ethyl hexanoate, and ethyl octanoate. However, differences were discovered between the strains as well as between the model and the actual systems. Overall, the isolated strains, particularly L. plantarum M22, have good fermentation characteristics and have the potential to become excellent Suanzhayu fermenters in the future. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the effect of papain on the physicochemical and microbiological properties, volatile compound profiles, and sensorial attributes of Chouguiyu. Papain was applied at a dose of 10, 50, 200, 400 U/g fish. Results showed that papain addition improved the release of free amino acids, essential amino acids, eicosapentaenoi acid (EPA, C20:5n3), and docosapentenoic acid (DPA, C22:5n6), respectively. Lower biogenic amines content, higher the volatile compound concentrations and relative abundance of Lactobacillales were also observed. Further results showed that the papain dose group decreased the fermentation time from 10 to 7 days while good organoleptic quality was remained, especially in the 200 U/g dose group. The redundancy analysis (RDA) showed a high correlation between Lactobacillus and the key volatile compounds in the 200 U/g and 400 U/g groups, which indicated that Lactobacillus could contribute to the fatty flavor. In summary, proper papain addition (i.e. 200 U/g or 400 U/g) could reduce biogenic amines contents and maintain acceptable sensorial properties of Chouguiyu in a shorter fermentation time. [Display omitted] [ABSTRACT FROM AUTHOR]

Chouguiyu (stinky Mandarin fish), a traditional spontaneously fermented fish in China, is famous for its unique aroma and pleasant taste. However, the relationships between the succession of microorganisms during the fermentation and the formation of Chouguiyu 's unique aroma and taste remain to be characterized. In this study, 16S rRNA gene amplicon sequencing was done to investigate the evolving microbiota during Chouguiyu fermentation, and the volatile compounds and amino acids profiles were measured alongside with chemical characterization of the samples (e.g., determination of pH, TVB-N, TBARS, and TCA-soluble peptides). Based on the changes of the microbiota, the fermentation was categorized into two stages: early-fermentation, 1st-3rd days; and late-fermentation, 4th-7th days. Linalool, piperitone, anethole, 1-octen-3-ol, 2-methyl-3-octanone and indole were identified as characteristic volatile compounds in Chouguiyu. According to the sensory evaluation results, the flavor of the Chouguiyu was reinforced in the late-fermentation stage. Redundancy analysis showed the relationships between evolving microbiota and the formation of Chouguiyu 's aroma and taste, and Psychrilyobacter was identified to be the most important bacterial genus contributing to flavor and aroma development, followed by Fusobacterium , Arcobacter and O c eanisphaera. These genera were positively correlated with Glu, Met, Tyr, Pro, linalool, piperitone, indole, TBARS, TVB-N, and TCA, and influenced the flavor and aroma of the Chouguiyu. The results of this study provided a scientific basis to further improve Chouguiyu production. • Chouguiyu 's fermentation process was divided into early-fermentation and late-fermentation. • The changes of features in Chouguiyu were more pronounced during the late-fermentation stage. • Four genera were found to be highly related to the change of Chouguiyu' s flavor and aroma. • These 4 genera included Psychrilyobacter , Fusobacterium , Arcobacter and Oceanisphaera. • The Psychrilyobacter was highly related to the flavor and aroma of Chouguiyu. [ABSTRACT FROM AUTHOR]

Decanal is one of the main products of lipid oxidation. It has been shown that decanal can oxidize to form volatiles with shorter carbon chains during heating, but the mechanism is still unclear. In this study, volatile compounds formed in the decanal thermal oxidation were verified using thermal-desorption cryo-trapping combined with GC–MS. A total of 32 volatile compounds were identified. The oxidation mechanism of decanal was studied by applying density functional theory. Results revealed that the carbonyl carbon atom was the thermal oxidation site of decanal and two pathways of peroxide oxidation were determined: the ortho‑carbon and the meta‑carbon oxidation. The ortho‑carbon oxidation pathway is superior to the occurrence of the meta‑carbon oxidation pathway. The oxidative mechanism of decanal was finally summarized as the peroxide oxidation based on radical attack on the carbonyl carbon, which would provide a theoretical basis for exploring the oxidation mechanism of other saturated aldehydes. [Display omitted] • Carbonyl carbon atom was the thermal oxidation site of decanal. • Oxidative cleavage of decanal was caused by peroxides formed by free radical attack. • Ortho‑carbon and meta‑carbon oxidation pathways were elaborated. • Priority order was ortho‑carbon oxidation pathway > meta‑carbon oxidation pathway. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermal oxidation mechanism of (E)−2-decenal was discussed by applying DFT. • Obtained reactions grouped into peroxide, alkoxy radical, peroxyl radical pathway. • Priority order is alkoxy radical > peroxide > peroxyl radical pathway. Unsaturated fatty aldehydes are the main products of fatty acid oxidation, and could be further oxidized to form volatile compounds with shorter carbon chains. Therefore, studying the oxidation of unsaturated fatty aldehydes is an important way to reveal the mechanism of food flavor formation during heating. In this study, volatile profiling of (E)-2-decenal during heating was firstly investigated by using thermal-desorption cryo-trapping combined with gas chromatography-mass spectrometry (GC–MS). A total of 38 volatile compounds were detected. Then, twenty-one reactions in the heating process of (E)-2-decenal were obtained by using density functional theory (DFT) calculations, and grouped into three oxidation pathways, namely, peroxide pathway, peroxyl radical pathway and alkoxy radical pathway. Meanwhile, the priority of these three pathways was the alkoxy radical reaction pathway > peroxide pathway > peroxyl radical reaction pathway. Moreover, the calculated results agreed well with the experimental results. [ABSTRACT FROM AUTHOR]

Little is known about the relationship between the chemical and microbial properties of Chouguiyu, a traditional Chinese fermented fish with unique aroma and plentiful taste. Therefore, we explored this relationship by determining the bacterial and fungal distribution of 14 brands of Chouguiyu. The distribution of microorganism and their effect on product quality, such as volatile flavor compounds (VFCs), free amino acids (FAA), physicochemical features and organoleptic properties were evaluated. Five VFCs (2-ethyl-1-hexanol, eucalyptol, 1-octen-3-ol, nonanal and indole) and three FAAs (Glu, Vla and Ala) were considered as core components. LAB (Vagococcus and Lactococcus) were found to contribute greatly to critical aroma formation and inhibition of TVB-N, leading to a moderate fermentation and good quality. While excessive increases in TVB-N, VFCs and FAA contents were found to be related with Psychrilyobacter and Fusobacterium , leading to poor organoleptic properties. The addition of Sufu to these products may be associated with the accelerating the fermentation process. Moderate fermentation with LAB is beneficial to typical aroma and good organoleptic properties, while excessive fermentation related with Psychrilyobacter and Fusobacterium may lead to overpowering flavors and lowered organoleptic properties. • Bacterial and fungi diversities were firstly studied among different Chouguiyu. • Psychrilyobacter and Fusobacterium might be related with overfermentation. • Moderate fermentation lead to typical aroma and good organoleptic properties. [ABSTRACT FROM AUTHOR]

Flavourzyme is known to promote protein decomposition, resulting in more peptides and amino acids which can improve the quality of fermented foods. In this study, the effects of flavourzyme addition on the fermentation of Suanzhayu fish were investigated. The results showed that the addition of 50 U/g flavourzyme reduced the water activity (a w) of products and promoted the release of trichloroacetic acid (TCA)-soluble peptides and free amino acids (FAAs). Thus, the stability of the product was improved and its nutritional value was increased. In addition, with the addition of flavourzyme, Lactobacillus and Saccharomyces more quickly became the dominant genera in the fermentation. Furthermore, the formation of alcohols, aldehydes, and esters was promoted in flavourzyme addition group. Redundant analysis (RDA) indicated that Lactobacillus and Lactococcus play important roles in the formation of flavors, especially for the characteristic flavors of Suanzhayu. Flavourzyme addition may be a novel method to greatly improve the properties of Suanzhayu and shorten the fermentation time. • The addition of 50 U/g flavourzyme help prolong the shelf life and increased the nutritional value. • Lactobacillus and Saccharomyces were easier to establish dominant position with flavourzyme addition. • Flavourzyme addition prompted the formation of alcohols, aldehydes, and esters. • Lactobacillus and Lactococcus played important roles in the flavor formation. • Flavourzyme addition may be a novel method that can potentially improve the properties of Suanzhayu. [ABSTRACT FROM AUTHOR]

• Firmicutes and Cyanobacteria were major phylum in Suancai. • Lactobacillus and Pediococcus were the biomarker of LS and HS, respectively. • Lactobacillus and Pediococcus were correlated with flavors in Suancai. • The inoculated of P. pentosaceus improve the alcohols and nitriles in Suancai. • The co-inoculated of L. plantarum and P. pentosaceus improve the flavors in Suancai. Suancai, a popular traditional fermented cabbage in northeast China, is commonly prepared by the spontaneous fermentation process at a certain salt concentration. The salt can affect the metabolites by affecting the microorganisms during Suancai fermentation. The bacterial community and volatile flavor compounds in commercial Suancai from different regions of Northeastern China at different salt concentrations were investigated using next-generation sequencing and GC–MS. Firmicutes and Cyanobacteria were the dominant phyla in the commercial Suancai, and Lactobacillus , Pediococcus , and Leuconostoc were the dominant genera. Among them, Lactobacillus and Pediococcus were considered as the biomarkers of the low and high salt Suncai, respectively. Eighty-five volatile flavor compounds were detected, and HS exhibited higher contents of volatile flavor compounds than LS. Based on the results of correlation analysis, Pediococcus were highly correlated with the alcohols and nitriles in Suancai. The contents of alcohols and nitriles significantly increased in the Suancai, fermented by Pediococcus pentosaceus. The co-inoculated fermentation of Lactobacillus plantarum and P. pentosaceus could increase the concentrations of alcohols, esters, aldehydes, hydrocarbons, and nitriles in Suancai. This study provides a perspective for understanding the ecology of Suancai fermentation and facilitating the fermentation with multispecies inoculation fermentation at an appropriate salt concentration. [ABSTRACT FROM AUTHOR]

The bacterial diversity and volatile flavor compounds (VFCs) during suancai fermentation in different temperatures were investigated by Illumina Hiseq sequencing and GC-MS. Firmicutes and Proteobacteria were observed to be the dominant phyla during the fermentation. Lactobacillus , Serratia , Leuconostoc , Pseudomonas , Pseudomonas , Pediococcus , etc., were observed as the main genus. Serratia and Pseudomonas predominated the early stage of suancai fermentation, while Lactobacillus predominated the later stage. Leuconostoc predominated the fermentation at 10 °C and 15 °C, while Weissella and Lactococcus predominated at 20 °C and 25 °C. A total of 86 VFCs were detected in all suancai samples. With the increase of the fermentation temperature, the kinds of VFCs were also increased. Lactobacillus , Pediococcus , Lactococcus , Brochothrix , Psychrobacter , Pseudoalteromonas , Acinetobacter and Enterobacter were the important bacteria related to VFCs during the fermentation. The bacteria were highly correlated with the VFCs in suancai fermentation. As the most dominant genus, Lactobacillus was significantly positive correlated with 13 VFCs. The correlation between the bacteria and VFCs in suancai could be used to search for microbial markers. In conclusion, 20 °C could accelerate the maturation and improve the sensory quality of suancai. This study could provide useful guidelines for screening of strains that contribute to the flavor formation in suancai fermentation. • Firmicutes and Proteobacteria were observed as dominant phylum in suancai. • Lactobacillus predominated the later stage of the suancai fermentation. • The biomarkers in suancai fermented under different temperature were different. • Eight important genera were significant correlated with the VFCs in suancai. • Lactobacillus was significant positive correlated with 13 VFCs in suancai. [ABSTRACT FROM AUTHOR]

This study was designed to explore the temperature effects on bacterial communities and metabolites, as well as their relationships during the fermentation of sour meat, a traditional fermented meat product in the ethnic minority regions of China. Results showed that reduction of pH and increase of lactic acid and free amino acid contents occurred (p < 0.05) as the fermentation temperature and time increased, and the tendency was more apparent at higher temperature. During the fermentation, Lactobacillus gradually replaced other genera, and higher the temperature, more rapid was the process. Both the number and amount of volatile organic compounds increased at higher temperatures. Hexanal, benzaldehyde, nonanal, (E,E)-2,4-decadienal, 1-octen-3-ol and octanal were identified as the key volatile organic compounds produced by Lactobacillus in sour meat as main contributors to odor as confirmed by variable importance in the projection analysis. Redundancy analysis and Pearson correlation showed positive correlation between Lactobacillus and desired product characteristics, such as higher content of lactic acid, free amino acids, volatile organic compounds, and lower pH and water activity values, which may represent a better quality and longer shelf life after fermentation at higher temperature. Therefore fermentation at 20 °C and 25 °C are proposed as optimum temperatures for sour meat production. • Faster fermentation process of sour meat were obtained at higher temperatures (20 °C and 25 °C). • There were more abundant metabolites in batches of higher fermentation temperatures. • Lactobacillus was the dominant genus eventually. • Lactobacillus was positively related to the desirable quality and flavor of sour meat. [ABSTRACT FROM AUTHOR]