Xin Nie

Objectives: The primary objective of this study was to investigate the effects of Macrococcus caseolyticus isolated from Chinese bacon on the quality of Chinese-style sausages. Methods: The physicochemical properties and volatile flavor compounds (VOCs) of sausages inoculated with M. caseolyticus at different concentrations (10⁵, 10⁶, and 10⁷ CFU/g) were investigated. VOCs were detected using gas chromatography–ion mobility spectrometry (GC-IMS). Results: The sausages inoculated with M. caseolyticus showed progressive decreases in Aw, total volatile base nitrogen (TVB-N), malondialdehyde and carbonyl content during fermentation compared to the control sausage. A total of 90 VOCs were identified based on GC-IMS analysis, including 20 esters, 17 aldehydes, 22 alcohols, 12 ketones, 5 acids compounds, and 14 other compounds. M. caseolyticus-inoculated sausages exhibited elevated levels in alcohols and aldehydes, while the content of ketones was reduced compared to the control sausage. Multivariate statistical analysis indicated the significant differences in volatile flavor profiles among the sample and control sausages. Notably, seven VOCs in sausages, including 1-octen-3-ol, isoamyl alcohol, heptanal, hexanal, methyl 2-methylbutyrate, ethyl isovalerate and 2-pinene, were identified as the key aroma compounds (ROAV ≥ 1). Conclusions: The fermented sausages inoculated with different concentrations of M. caseolyticus exhibited significant differences in VOCs. This study provides the support for employing M. caseolyticus to improve the overall quality and flavor profile of Chinese-style sausage.

Background : Feces and cecum content are commonly involved in metabolomic analysis to understand the gut metabolic profile of the host, while, in fact, they are different. Feces represent the terminal excretory product after extensive host enzymatic digestion, absorption, and significant modification by the distal gut microbiota. In contrast, cecum content reflects the localized, in situ metabolic microenvironment at that specific site. However, it is worth noting that feces are the most accessible sample type for non-invasive studies, which could be considered proxies for cecum content in some specific cases. Unfortunately, the validity of fecal samples as an alternative to cecum content has rarely been assessed. Methods: The current study attempted to illustrate the distinct metabolomic and microbiota features of feces and cecum content in eight animals (mouse, pig, chicken, duck, rabbit, Gansu yak, Sichuan yak, and sheep) by means of ¹H-NMR and 16S rRNA, respectively. Results: A total of 116 molecules were characterized in feces and cecum content samples. Among them, 22 molecules were shared in all groups. Taking advantage of the univariate analysis, twenty-seven of the quantified molecules were significantly different between feces and cecum content, mainly pertaining to amino acids and organic acids. Moreover, in terms of mammals and non-mammals, short-chain fatty acids could be considered the main factor discriminating the metabolomic profiles between feces and cecum content. Furthermore, to better understand the mechanism of their metabolomic differences, 16S rRNA sequencing analysis was performed on feces and cecum content samples of mice, which is the most widely used animal model. The result showed that the Ace, Shannon, and Sobs indexes in feces were significantly higher than those of cecum content (p < 0.05). At the phylum and genus levels, the microbiota structures of feces and cecum content were similar, while the relative abundances of their microbiota exhibited distinct features. Conclusions: The present study could reduce this gap in information by characterizing, for the first time, the metabolomic differences between feces and cecum content using ¹H-NMR. Moreover, this study is meant as a reference guide for researchers wishing to apply a metabolomics approach to the gut of the host.

To investigate the dynamic changes and potential correlations between microbial diversity and volatile organic compounds (VOCs) during Chinese medium-temperature Daqu (MTD) manufacturing at different key stages, in this study, high-throughput sequencing (HTS) and gas chromatography–ion mobility spectrometry (GC–IMS) were employed to analyze the microbial diversity and VOCs of MTD, respectively. The results showed that Weissella, Staphylococcus, Thermoactinomyces, Kroppenstedtia, and Lactobacillus were the dominant bacterial genera, while Aspergillus, Alternaria, Thermoascus, Thermomyces, Wickerhamomyces, and Saccharomyces were the dominant fungal genera. A total of 61 VOCs were detected by GC–IMS, among which, 13 differential VOCs (VIP > 1) were identified, that could be used as potential biomarkers to judge the fermentation stage of MTD. Kroppenstedtia and Saccharopolyspora were positively correlated with 3-methyl-2-butenal and 2,2,4,6,6-pentamethylheptane-D, respectively, and both of these were positively correlated with butanal-D. Acetobacter, Streptomyces, and lactic acid bacteria (LAB) including Leuconostoc, Pediococcus, Weissella, and Lactobacillus were negatively correlated with their associated VOCs, while fungi were generally positively correlated with VOCs. Wickerhamomyces, Saccharomyces, and Candida were positively correlated with butan-2-one-M. This study provides a theoretical basis for explaining the mechanisms of MTD flavor formation and screening functional microorganisms to improve the quality of MTD.

Low-temperature and low-salt fermented Chinese kohlrabi (LSCK) represents a novel approach to producing low-salt kohlrabi without the need for desalination during processing, as compared to traditional techniques. However, the profile of its non-volatile metabolites remains unclear. In order to investigate the non-volatile metabolites and their changes in LSCK during fermentation, the LSCKs fermented for 0 day (0D), 45 days (45D) and 90 days (90D) were analyzed using LC-MS/MS non-targeted metabolomics coupled with multivariate statistical analysis. The results showed that 60, 74, and 68 differential metabolites were identified in the three groups A1 (0D and 45D), A2 (0D and 90D), and A3 (45D and 90D) (VIP >1, p < 0.05, Log2FC >1), respectively. The differential metabolites were mainly amino acids, peptides, and analogues, fatty acyls, organic acids and derivatives, and carbohydrates and carbohydrate conjugates. Seventeen common differential metabolites were identified in A1, A2, and A3 groups. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis suggested that the alanine, aspartate and glutamate metabolism, butanoate metabolism, α-linolenic acid metabolism, arginine biosynthesis, and phenylalanine metabolism were significantly correlated with the differential metabolites. The present study elucidates for the first time the changes in non-volatile differential metabolites and their associated metabolic pathways in the novel Chinese low-salt kohlrabi, providing a theoretical basis for improving the industrial fermentation process of this innovative product.

Kiwi wine (KW) is tipically made by fermenting juice from peeled kiwifruit, resulting in the disposal of peel and pomace as by-products. However, the peel contains various beneficial compounds, like phenols and flavonoids. Since the peel is edible and rich in these compounds, incorporating it into the fermentation process of KW presents a potential solution to minimize by-product waste. This study compared the aroma and taste profiles of KW from peeled (PKW) and unpeeled (UKW) kiwifruits by combining intelligent sensory technology, GC-MS, and ¹H-NMR. Focusing on aroma profiles, 75 volatile organic compounds (VOCs) were identified in KW fermented with peel, and 73 VOCs in KW without peel, with 62 VOCs common to both. Among these compounds, rose oxide, D-citronellol, and bornylene were more abundant in UKW, while hexyl acetate, isoamyl acetate, and 2,4,5-trichlorobenzene were significantly higher in PKW. For taste profiles, E-tongue analysis revealed differences in the taste profiles of KW from the two sources. A total of 74 molecules were characterized using ¹H-NMR. UKW exhibited significantly higher levels of tartrate, galactarate, N-acetylserotonin, 4-hydroxy-3-methoxymandelate, fumarate, and N-acetylglycine, along with a significantly lower level of oxypurinol compared to PKW. This study seeks to develop the theoretical understanding of the fermentation of kiwifruit with peel in sight of the utilization of the whole fruit for KW production, to increase the economic value of kiwifruit production.

To investigate the diversity and dynamics of microorganisms in Chinese fresh beef (CFB) without acid discharge treatment during cold storage, high-throughput sequencing was employed to analyze the CFB refrigerated for 0, 3, 7, and 10 days. The results showed that the community richness of the fungi and bacteria decreased significantly. However, the diversity decreased in the early stage and increased in the later stage. At the phylum level, Ascomycota (74.1–94.1%) and Firmicutes (77.3–96.8%) were the absolutely dominant fungal and bacterial phyla. The relative abundance of both fungal and bacterial phyla displayed a trend of increasing and then decreasing. At the genus level, Candida (29.3–52.5%) and Lactococcus (19.8–59.3%) were, respectively, the dominant fungal and bacterial genera. The relative abundance of Candida showed a trend of increasing and then decreasing, while Lactococcus possessed the opposite trend. KEGG metabolic pathways analysis suggested that carbohydrate metabolism, membrane transport, and amino acid metabolism were the major metabolic pathways of bacteria. Bugbase prediction indicated the major microbial phenotype of bacteria in CFB during cold storage was Gram-positive (17.2–31.6%). Correlation analysis suggested that Lactococcus, Citrobacter, Proteus, and Rhodotorula might be the main microorganisms promoting the production of off-flavor substances in CFB. This study provides a theoretical basis for the preservation of Chinese fresh beef.

Guizhou sour meat and sour fish, Chaoshan fish sauce, Sichuan sausage and bacon, Cantonese sausage, Jinhua ham, and Xinjiang air-dried beef are eight representatives of Chinese traditional fermented meat and fish products (FMFPs), which are favored by Chinese consumers due to their high nutritional value and quality. The quality of the spontaneously fermented Chinese traditional FMFP is closely correlated with microorganisms. Moreover, the dominant microorganisms are significantly different due to regional differences. The effects of microorganisms on the texture, color, flavor, nutrition, functional properties, and safety of Chinese traditional FMFPs have not been not fully described. Additionally, metabolic pathways for flavor formation of Chinese traditional FMFPs have not well been summarized. This article describes the seven characteristic Chinese traditional FMFPs and correlated dominant microorganisms in different regions of China. The effects of microorganisms on the texture, color, and flavor of Chinese traditional FMFPs are discussed. Furthermore, the metabolic pathways of microbial regulation of flavor formation in Chinese traditional FMFPs are proposed. This work provides a theoretical basis for improvement of Chinese traditional FMFPs by inoculating functional microorganisms isolated from Chinese traditional fermented foods.

The objective of this study was to explore the microbial diversity, volatile flavor substances, and their potential correlations in inner and surface Chinese Qingcheng Mountain traditional bacon (CQTB). The results showed that there were 39 volatile flavor substances in inner and surface CQTB detected by headspace solid-phase microextraction and gas chromatography–mass spectrometry (HS-SPME-GC-MS). Moreover, significant differences in volatile flavor substances between the inner and surface CQTB were observed. Sixteen key volatile flavor substances were screened (OAV > 1), including guaiacol, nonanal, ethyl isovalerate, and others. High-throughput sequencing (HTS) result indicated that Firmicutes, Proteobacteria, and Actinobacteria were the predominant bacterial phyla, and Ascomycota and Mucoromycota were the predominant fungal phyla. Staphylococcus, Psychrobacter, and Brochothrix were the predominant bacteria, and Debaryomyces, Penicillium, and Mucor were the predominant fungal genera. Spearman correlation coefficient analysis suggested that Apiotrichum and Lactobacillus were closely and positively correlated with the formation of key phenol compounds. The present work demonstrates the microbial diversity and related volatile flavor substances and their potential correlations in CQTB and provides a theoretical basis for the development of microbial starter culture and green processing of CQTB.

A novel Chinese-style sausage with Chinese traditional fermented condiments used as additional ingredients is produced in this study. The aim of this study was to investigate the microbial community’s structure, the volatile flavor substances and their potential correlation in the novel Chinese sausage. High-throughput sequencing (HTS) and solid-phase microextraction-gas chromatography-mass spectrometry (GC-MS) were, respectively, used to analyze the microbial diversity and volatile flavor substances of the novel Chinese-style sausage during storage. The results showed that Firmicutes, Proteobacteria and Actinobacteria were the predominant bacterial genera, and Hyphopichia and Candida were the predominant fungal genera. A total of 88 volatile flavor substances were identified through GC-MS, among which 18 differential flavor compounds were screened (VIP > 1), which could be used as potential biomarkers to distinguish the novel sausages stored for different periods. Lactobacillus exhibited a significant negative correlation with 2,3-epoxy-4,4-dimethylpentane and acetoin and a significant positive correlation with 2-phenyl-2-butenal. Hyphopichia significantly positively correlated with ester. Leuconostoc significantly positively correlated with ethyl caprate, ethyl palmate, ethyl tetradecanoate and ethyl oleate while it negatively correlated with hexanal. This study provides a theoretical basis for revealing the flavor formation mechanisms and the screening of functional strains for improving the flavor quality of the novel Chinese-style sausage.

This study aimed to investigate the effects of ultra-long-term fermentation on the formation of non-volatile metabolites of Chinese solid-fermented kohlrabies. Liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) based non-targeted metabolomics coupled with multivariate statistical analysis were employed to respectively analyze the kohlrabies solid fermented for 5 years (5Y), 8 years (8Y), and 11 years (11Y). The results showed that 31, 169, and 123 differential metabolites were identified in the three groups of 5Y and 8Y (A1), 5Y and 11Y (A2), and 8Y and 11Y (A3), respectively (VIP > 1, p < 0.05 and |log₂FC| > 1). The differential non-volatile metabolites were mainly organic acids and derivatives, organoheterocyclic compounds, benzenoids, lipids and lipid-like molecules, and organicoxygen compounds. Furthermore, 11 common differential metabolites were screened in the three groups, including diaminopimelic acid, ectoine, 9,10,13-TriHOME, and 9 others. The citrate cycle, glycine, serine and threonine metabolism, pantothenate and CoA biosynthesis, and glyoxylate and dicarboxylate metabolism were the four pathways most significantly correlated with the differential non-volatile metabolites based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis (p < 0.05). The present study describes the effects of ultra-long-term fermentation periods on the formation of non-volatile metabolites in solid fermented kohlrabies, providing a theoretical basis for cooking with the three solid fermented kohlrabies to make different Chinese dishes.