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In order to investigate the changes of volatile flavor substances in the process of beeves spoilage, beeves with different storage time were employed. The volatile flavor substances of beeves in spoilage process were analyzed by using gas chromatography ion transfer spectroscopy (GC-IMS) and electronic nose. The results showed that a total of 55 volatile flavor substances were detected through GC-IMS, mainly including 12 ketones, 10 alcohols, 9 esters, 8 aldehydes and 4 hydrocarbons. GC-IMS and electronic nose analysis indicated that the types and contents of volatile flavor substances significantly increased during the spoilage process. The alcohols, aldehydes, esters, acids, furans, pyrroles, thiophenes, amines, pyridines and ethers continuously increased during the spoilage process. However, ketones, hydrocarbons, and sulfur compounds gradually increased and reached peak at the seventh day, and then gradually decreased. PCA and PLS-DA analysis suggested that there were significant differences in volatile flavor substances of beeves in spoilage process. Sixteen different volatile flavor substances were identified by variable importance for the projection (VIP) value, with the extension of storage, the contents of irritating and unpleasant flavor substances such as n-hexanal-D, n-hexanal-M, butyraldehyde-M, butyraldehyde-D, tetrahydropyrrole-M, isoamyl-D, isoamyl-M, n-propanol-D, 2,3-butanedione gradually increased, which could be used as potential biomarkers to distinguish beeves with different degrees of spoilage. This work provides a theoretical basis for monitoring beef spoilage process.

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 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.

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.

In order to test the effects of the crude extracts from Rhodobacter sphaeroides (CCRS) on the volatile flavor substances and flavor amino acids of sausages during storage, the sausages were respectively processed with addition of CCRS at higher, medium and lower concentrations. Sausage processed without addition of CCRS was used as control. The volatile flavor substances and free amino acids were respectively analyzed using headspace solid-phase micro-extraction gas chromatography mass spectrometry (HS-SPME-GC-MS) and amino acid analyzer. The experimental results showed that a total of 36 volatile flavor substances were detected by GC-MS, including 17 alcohols, 1 ester, 10 aldehydes, 2 acids, 3 alkanes and 3 other components, among which 8 substances were considered the main flavor substances. Multivariate statistical analysis showed that the content and types of alcohols in sausages added CCRS were lower than those in control after 3 months storage. After 6 months storage, the alcohol content in the sausages with CCRS was higher than that of the control. However, the aldehyde content of the sausages with CCRS was lower than that of the control. Moreover, the CCRS promoted the production of ethenyl hexanoate, which was the only one ester in the sausages. On the other hand, the addition of low concentration of CCRS reduced the content of heptaldehyde, octanoic acid and other odor substances. Amino acid analysis suggested that the CCRS increased the proportion of delicate and sweet amino acids. The taste activity value (TAV) analysis indicated that the histidine TAV value was the strongest and had the greatest impact on sausage taste. The present study would provide a theoretical basis and technical support for enhancing the flavor quality of Chinese traditional sausages based on the metabolites of Rhodobacter sphaeroides.

In order to investigate the effect of natural air-drying on the quality and flavor of raw mustard roots, the moisture content, water activity, hardness, crispness, protein content, amino acid nitrogen content, total plate count and total lactic acid bacteria were measured and compared before and after air-drying of the raw mustard roots. The changes of volatile flavor substances were analyzed by solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC-MS). The results showed that the hardness of mustard roots after natural air-drying was significantly enhanced and the crispness was reduced (P1, P

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.

A low-temperature and low-salt industrially fermented Chinese kohlrabi (LSCK) was developed in this study, with the salt usage decreased by approximately 70% compared to the traditional high-salt fermented Chinese kohlrabi (HSCK). The differences in physicochemical properties, metabolites and overall flavors during LSCK fermented for 0, 45 and 90 days (d) were analyzed by gas chromatography-time-of-flight mass spectrometry (GC-TOF-MS), electronic nose (E-nose) and other techniques. The results showed that the total acid content increased significantly from 3.68 to 8.59 g/kg. However, the protein content significantly decreased from 2.52/100 to 0.66 g/100 g. The number of lactic acid bacteria cells increased significantly from 3.69 to 4.46 log10CFU/g. Based on multivariate statistical analysis, 21, 14, and 15 differential metabolites were identified in the three treatment groups A1 (0 and 45 days), A2 (45 and 90 days), and A3 (0 and 90 days) respectively (VIP > 1, p

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.

To explore the effect of low-temperature and low-salt fermentation on the volatile flavor substances of Chinese kohlrabi, low-temperature and low-salt fermented Chinese kohlrabi (LSCK) and traditional high-salt fermented Chinese kohlrabi (HSCK) were produced. The physicochemical and texture properties of the two kinds of Chinese kohlrabies were evaluated. Headspace gas chromatography-ion mobility spectrometry (GC-IMS) and electronic nose (E-nose) were used to analyze the volatile flavor substances of the kohlrabi. The results showed that the total acid content significantly decreased (p < 0.05), while protein and reducing sugar contents significantly increased (p < 0.05) by low-temperature and low-salt fermentation. A total of 114 volatile flavor substances were identified. The alcohol, ketone, pyrazine, ether, and nitrile contents in LSCK were significantly higher than those in HSCK (p < 0.05). Moreover, the unpleasant flavor from the 3-methylbutyric acid formation was effectively depressed in LSCK. The principal component analysis (PCA) and orthogonal partial least squares discrimination analysis (OPLS-DA) models established by multivariate statistical analysis significantly distinguished the two types of kohlrabies. Multivariate statistical analysis suggested that 16 volatile flavor substances with VIP >1, including tetrahydrothiophene, ethyl 3-(methylthio)propanoate, 3-methylbutyric acid, hexanenitrile, and 3-methyl-3-buten-1-ol, could be used as potential biomarkers for identifying LSCK and HSCK. The E-nose analysis further demonstrated that there was a significant difference in overall flavor between the LSCK and HSCK. The present study provides support for the development of green processing technology and new low-salt Chinese kohlrabi products.

Fermented kohlrabi is a very popular side dish in China. Chinese kohlrabies industrially fermented for 0 years (0Y), 5 years (5Y), and 10 years (10Y) were employed and analyzed by non-targeted metabolomics based on GC-TOF-MS, and the differential metabolites were screened using multivariate statistical analysis techniques, including principal component analysis (PCA) and orthogonal partial least squares discrimination analysis (OPLS-DA). The results showed that 47, 38, and 33 differential metabolites were identified in the three treatment groups of 0Y and 5Y (A1), 0Y and 10Y (A2), and 5Y and 10Y (A3), respectively (VIP > 1, p < 0.05). The metabolites were mainly carbohydrates, amino acids, and organic acids. Furthermore, 13 differential metabolites were screened from the three groups, including L-glutamic acid, L-aspartic acid, γ-aminobutyric acid, and other compounds. Four metabolic pathways termed alanine, aspartate, and glutamate metabolism, arginine biosynthesis, arginine and proline metabolism, and glycolysis/gluconeogenesis were the most significant pathways correlated with the differential metabolites, as analyzed according to the Kyoto Encyclopedia of Genes and Genomes (KEGG). The odors for the three ultra-long-term industrially fermented kohlrabies were significantly different, as detected by E-nose. The present work describes the changes in metabolites between different ultra-long-term industrially fermented kohlrabies and the associated metabolic pathways, providing a theoretical basis for the targeted regulation of characteristic metabolite biosynthesis in Chinese fermented kohlrabi.

Modeling the impact of space weather events such as coronal mass ejections (CMEs) is crucial to protecting critical infrastructure. The Space Weather Modeling Framework is a state-of-the-art framework that offers full Sun-to-Earth simulations by computing the background solar wind, CME propagation, and magnetospheric impact. However, reliable long-term predictions of CME events require uncertainty quantification (UQ) and data assimilation. We take the first steps by performing global sensitivity analysis (GSA) and UQ for background solar wind simulations produced by the Alfvén Wave Solar atmosphere Model (AWSoM) for two Carrington rotations: CR2152 (solar maximum) and CR2208 (solar minimum). We conduct GSA by computing Sobol' indices that quantify contributions from model parameter uncertainty to the variance of solar wind speed and density at 1 au, both crucial quantities for CME propagation and strength. Sobol' indices also allow us to rank and retain only the most important parameters, which aids in the construction of smaller ensembles for the reduced-dimension parameter space. We present an efficient procedure for computing the Sobol' indices using polynomial chaos expansion surrogates and space-filling designs. The PCEs further enable inexpensive forward UQ. Overall, we identify three important model parameters: the multiplicative factor applied to the magnetogram, Poynting flux per magnetic field strength constant used at the inner boundary, and the coefficient of the perpendicular correlation length in the turbulent cascade model in AWSoM. [ABSTRACT FROM AUTHOR]

Cas9, the RNA-guided DNA endonuclease from the CRISPR-Cas (clustered regularly interspaced short palindromic repeat-CRISPR-associated) system, has been adapted for genome editing and gene regulation in multiple model organisms. Here we characterize a Cas9 ortholog from Streptococcus thermophilus LMG18311 (LMG18311 Cas9). In vitro reconstitution of this system confirms that LMG18311 Cas9 together with a trans-activating RNA (tracrRNA) and a CRISPR RNA (crRNA) cleaves double-stranded DNA with a specificity dictated by the sequence of the crRNA. Cleavage requires not only complementarity between crRNA and target but also the presence of a short motif called the PAM. Here we determine the sequence requirements of the PAM for LMG18311 Cas9. We also show that both the efficiency of DNA target cleavage and the location of the cleavage sites vary based on the position of the PAM sequence. [ABSTRACT FROM AUTHOR]