Changes in free amino acids of fermented minced peppers during natural and inoculated fermentation process based on HPLC-MS/MS

Effect of Rhodotorula mucilaginosa inoculation on the aroma development of a fermented vegetables simulated system

Fermented vegetables are known for their unique flavors and aromas, which are influenced by the complex microbial processes that occur during fermentation. Rhodotorula mucilaginosa is a red yeast strain that is frequently isolated from fermented vegetables. However, the specific mechanisms underlying their effects on aroma production remain unclear. In this study, a simulated system of vegetables fermented using vegetable juices was used to investigate the effects of R. mucilaginosa inoculation on aroma development. The results demonstrated that this red yeast strain could utilize the nutrients present in the vegetable juices to support its growth and reproduction. Moreover, the inoculation of fermented vegetable juices with this yeast strain led to an increase in the levels of umami amino acids and sweet amino acids. Furthermore, this yeast strain was found able to significantly reduce the content of sulfur-containing compounds, which may decrease the unpleasant odor of fermented vegetables. Additionally, the yeast strain was capable of producing high concentrations of aromatic compounds such as phenylethyl alcohol, methyl 2-methylbutyrate, methyl butyrate, and nonanoic acid in a minimum medium. However, only phenylethyl alcohol has been identified as a core aromatic compound in fermented vegetable juice. The three fermented vegetable juices exhibited significantly different flavor profiles according to comparative analysis. Therefore, the core flavor compounds found in fermented vegetables are primarily derived from the release and modification of endogenous flavors naturally present in the vegetables, facilitated by the yeast during fermentation.

Investigating the mechanism of the flavor formation in Sichuan sun vinegar based on flavor-orientation and metagenomics

Fermentation and aging are the key stages of flavor formation in Sichuan sun vinegar (SSV), but the generation mechanisms of the flavor produced by these processes are unknown. However, complex microbial metabolism is critical to the flavor development of SSV. In this study, we analyzed the key flavor compounds present in SSV. Combined with odor activity value (OAV), the main aroma components of SSV were screened, and the relationship between microorganisms and key flavor formation was predicted using metagenomic sequencing technology. The results revealed 38 key flavor compounds in SSV. Lactobacillus, Weissella, Acetobacter, Lichtheimia, Pediococcus, Oenococcus, Brettanomyces, Kazachstania, Pichia, Xanthomonas, Lenconostoc are widely involved in the production of key flavor compounds such as 2,3-butanediol, 2-Furanmethanol, phenylethanol, 3-(Methylthio)-1-propanol, acetic acid, lactic acid, butyric acid, isovaleric acid and other organic acids. Among them, Lichtheimia and Lactobacillus are important genera for the degradation of starch, arabinoxylan and cellulose. The acetaldehyde,4-ethyl-2-methoxy-phenol and 2-methoxy-4-methyl-phenol production pathway may be related to Lactobacillus, Acetobacter and Brettanomyces. This study provides a new understanding of the key flavor-formation stage and flavor compound generation mechanism of SSV and provides a reference for the screening and isolation of functional strains and the reconstruction of microbial communities.

Insights into the metabolic profiling of Polygonati Rhizoma fermented by Lactiplantibacillus plantarum under aerobic and anaerobic conditions using a UHPLC-QE-MS/MS system

Introduction

Polygonati Rhizoma is a multi-purpose food with medicinal uses. Fermentation of Polygonati Rhizoma by lactic acid bacteria could provide new insights into the development of Polygonati Rhizoma products.

Methods

In this study, Lactiplantibacillus plantarum was fermented with Polygonati Rhizoma extracts in a bioreactor under aerobic and anaerobic conditions with pH and DO real-time detection. Metabolic profiling was determined by UHPLC-QE-MS/MS system. Principal component analysis and orthogonal partial least-squares discriminant analysis were used to perform multivariate analysis.

Results

A total of 98 differential metabolites were identified in broth after fermentation, and 36 were identified between fermentation under aerobic and anaerobic conditions. The main metabolic pathways in the fermentation process are ABC transport and amino acid biosynthesis. Most of the compounds such as L-arginine, L-aspartic acid, leucine, L-lysine, citrate, inosine, carnitine, betaine, and thiamine were significantly increased during fermentation, playing a role in enhancing food flavor. Compared with anaerobic fermentation, aerobic conditions led to a significant rise in the levels of some compounds such as valine, isoleucine, and glutamate; this increase was mainly related to branched-chain amino acid transaminase, isocitrate dehydrogenase, and glutamate dehydrogenase.

Discussion

Aerobic fermentation is more beneficial for the fermentation of Polygonati Rhizoma by L. plantarum to produce flavor and functional substances. This study is the first report on the fermentation of Polygonati Rhizoma by L. plantarum and provides insights that would be applicable in the development of Polygonati Rhizoma fermented products.

Anti-obesity effect of Angelica keiskei Jiaosu prepared by yeast fermentation on high-fat diet-fed mice

In this study, an Angelica keiskei (A. keiskei) Jiaosu (FAK) was prepared by yeast fermentation to investigate its anti-obesity effect on high-fat diet (HFD)-fed mice. 70 SPF grade male C57BL/6J mice were randomly divided into 7 groups (n = 10): blank control group (N), high-fat model group (M), positive control group (Orl), unfermented control group (NF), high-dose intervention group (FH), medium-dose intervention group (FM), and low-dose intervention group (FL). The results showed that FAK intervention significantly reduced the body weight, Lee's index and liver index of HFD-fed mice (P < 0.05). Compared with M group, the serum levels of triglyceride (TG), total cholesterol (TC), leptin and glucose (GLU) in FH group were remarkably decreased and that of interleukin-27 (IL-27) were increased (P < 0.05). The levels of TG, and TC in the liver of mice were also markedly decreased in the FH group (P < 0.05). HE staining results showed that the liver cells in the three intervention groups had less degeneration and fatty vacuoles in the cytoplasm, and the liver cords were orderly arranged compared with that of M group. Furthermore, FAK significantly inhibited epididymal adipose tissue cell expansion induced by HFD. FAK up-regulated the protein expression levels of p-AMPK and PPARα to promote lipolysis and down-regulated the expression of PPARγ to reduce lipid synthesis (P < 0.05). Additionally, the results of gut microbiota showed that after the intervention, a decrease trend of F/B value and Deferribacterota was noticed in the FH group compared with M group. At the genus level, FAK intervention significantly increased that of Ileiobacterium compared to the M group (p < 0.05). A rising trend of norank_f_Muribaculaceae, Lactobacillus, and Bifidobacterium were also observed in the HF group. Conclusively, these findings demonstrated that FAK intervention can effectively improve obesity in mice caused by HFD and the potential mechanisms was related to the regulation of serum levels of leptin and IL-27, lipogenesis and lipolysis in adipose tissue and gut microbiota composition.

High pressure processing improves the texture quality of fermented minced pepper by maintaining pectin characteristics during storage

Texture quality affects the sensory and market acceptance of fermentation minced pepper (FMP), but it will deteriorate during storage. Thus, high pressure processing (HPP) and thermal pasteurization (TP) were used to improve the texture quality of FMP during storage. The results showed that variations in texture quality and pectin characteristics under HPP and TP treatments were similar during storage. The hardness, cell wall material (CWM) and sodium carbonate-soluble pectin (SSP) content, water-soluble pectin (WSP) molecular weight (M_w ) decreased, while WSP content and sodium chelate-soluble pectin (CSP) M_w increased after storage. HPP-treated FMP showed higher hardness (66.64-85.95 N) than that in TP-treated one (57.23-62.72 N) during storage. Rhamnose (Rha), arabinose, mannose, and glucose were the crucial compositions in three pectins, and their total molar ratios, respectively, reached 89.19% and 87.97% after HPP and TP treatment. However, the molar ratio of most monosaccharide in three pectins decreased after storage. Atomic force microscope images indicated the short chains and branch structures increased but aggregates decreased in most pectin components during storage. Pearson correlation analysis demonstrated FMP hardness was extremely (p < 0.01) positively correlated with CWM and SSP content, and extremely (p < 0.01) negatively correlated with WSP content. Compared to TP treatment, HPP presented higher hardness, SSP content and M_w , Rha content, CSP M_w , and lower WSP content during storage. Hence, HPP was an effective method to improve the texture quality of FMP by maintaining pectin characteristics during storage. PRACTICAL APPLICATION: Softening is one of the main factors affecting market value and consumer preferences for FMP, and it is closely related to the modification and depolymerization of pectin. Changes of texture quality and pectin properties in HPP- and TP-treated FMP during storage were assessed, including hardness, the content, monosaccharide compositions, M_w distribution, and nanostructure of WSP, SSP, and CSP. Compared to TP treatment, HPP could effectively improve the texture quality of FMP by inhibiting pectin degradation during storage. All the findings presented in this study would help to provide new insights into regulating the texture quality of FMP.