Antifungal mechanisms investigation of lactic acid bacteria against Aspergillus flavus: through combining microbial metabolomics and co-culture system.

AIMS: To develop antifungal lactic acid bacteria (LAB) and investigate their antifungal mechanisms against Aspergillus flavus in aflatoxin (AF) production. METHODS AND RESULTS: We isolated 179 LABs from cereal-based fermentation starters and investigated their antifungal mechanism against A. flavus through liquid chromatography-mass spectrometry and co-culture analysis techniques. Of the 179 isolates, antifungal activity was identified in Pediococcus pentosaceus, Lactobacillus crustorum, and Weissella paramesenteroides. These LABs reduced AF concentration by (i) inhibiting mycelial growth, (ii) binding AF to the cell wall, and (iii) producing antifungal compounds. Species-specific activities were also observed, with P. pentosaceus inhibiting AF production and W. paramesenteroides showing AF B1 binding activity. In addition, crucial extracellular metabolites for selecting antifungal LAB were involved in the 2',3'-cAMP-adenosine and nucleoside pathways. CONCLUSIONS: This study demonstrates that P. pentosaceus, L. crustorum, and W. paramesenteroides are key LAB strains with distinct antifungal mechanisms against A. flavus, suggesting their potential as biological agents to reduce AF in food materials.

Analytical factors for eight short-chain fatty acid analyses in mouse feces through headspace solid-phase microextraction-triple quadrupole gas chromatography tandem mass spectrometry.

This study developed a method for quantifying eight short-chain fatty acids (SCFAs) in mouse fecal samples using solid-phase microextraction (SPME) coupled with triple quadrupole gas chromatography tandem mass spectrometry. Furthermore, significant factors affecting SCFA analysis, including SPME fiber selection, pH, salting-out agent, and sample collection time, were investigated. Contrary to previous studies, we found that the CAR/PDMS fiber had the highest extraction efficiency for all SCFAs. The optimal extraction efficiency was observed at pH 2.0, particularly for low-molecular-weight SCFAs. NaH2PO4 showed a more effective extraction efficiency than NaCl, owing to its pH stability and less interference with the solvent matrix. Additionally, our results showed that the SCFA concentration increased over collection time. The composition ratio of the eight SCFAs was maintained for up to 24 h; thus, we concluded that samples should be collected within four hours to obtain reliable results. Our findings may improve laboratory methods for SCFA extraction and mouse fecal sample analysis.

MicroRNA function in NK-cell biology.

The important role of microRNAs in directing immune responses has become increasingly clear. Here, we highlight discoveries uncovering the role of specific microRNAs in regulating the development and function of natural killer (NK) cells. Furthermore, we discuss the impact of NK cells on the entire immune system during global and specific microRNA ablation in the settings of inflammation, infection, and immune dysregulation.

Gellan gum prevents non-alcoholic fatty liver disease by modulating the gut microbiota and metabolites.

Gellan gum (GG) is an anionic polysaccharide used as an additive in the food industry. However, the effect of GG on gut microbiota regulation and nonalcoholic fatty liver disease (NAFLD) has not yet been investigated. In vitro fermentation experiments have demonstrated that GG promoted the growth of probiotic strains such as Lactiplantibacillus rhamnosus and Bifidobacterium bifidum, producing metabolites beneficial to gut health. In mice, GG reduced hepatic triglyceride content, serum biomarkers, and body fat mass and weight gain induced by a high fat diet. Additionally, GG regulated the gut microbiota including Desulfovibrionales, Deferribacterales, Bacteroidales, and Lactobacillales at the order level and also promoted short-chain fatty acid production. Moreover, GG improved the expression of proteins related to hepatic inflammation and lipid metabolism. Taken together, GG ameliorated NAFLD, possibly by acting on the gut-liver axis via improving the gut health, indicating its potential as a food supplement and/or prebiotic against NAFLD.

The Probiotic Effects of the Saccharomyces cerevisiae 28-7 Strain Isolated from Nuruk in a DSS-Induced Colitis Mouse Model.

Probiotics are microorganisms that can benefit host health when ingested in a live state, and lactic acid bacteria are the most common type. Among fungi, Saccharomyces boulardii (SB) is the only strain known to have a probiotic function with beneficial effects on colitis; however, information on other probiotic yeast strains is limited. Therefore, this study aimed to discover yeast strains expressing intestinal anti-inflammatory activities by exhibiting probiotic properties in dextran sodium sulfate (DSS)-induced colitis mice model. Nuruk (Korean traditional fermentation starter) containing various microbial strains was used as a source for yeast strains, and S. cerevisiae 28-7 (SC28-7) strain was selected with in vitro and in vivo characteristics to enable survival in the intestines. After 14 days of pretreatment with the yeast strains, DSS was co-administered for six days to induce colitis in mice. The results revealed that the disease activity index score was lowered by SC28-7 treatment compared to the DSS group, and the colon length and weight/length ratio were recovered in a pattern similar to that of the normal group. SC28-7 administration significantly reduced the secretion of pro-inflammatory cytokines in the serum and modified the mRNA expression of inflammatory cytokines (interleukin-1ß, transforming growth factor-ß, and interferon-γ) and proteins involved in gut barrier functions (mucin 2, mucin 3, zonula occludens-1, and occludin) in colon tissues. These results indicate that SC28-7 attenuates DSS-induced colon damage and inflammation, supporting its future use as a probiotic yeast for treating and preventing intestinal inflammatory diseases such as inflammatory bowel disease.

Untargeted Metabolomics reveals Doenjang metabolites affected by manufacturing process and microorganisms.

Doenjang is a traditional Korean fermented soybean-based food that is now produced industrially as traditional Doenjang and modernized Doenjang, depending on the conditions of the manufacturing process. In this study, the effect of the production process on Doenjang metabolites was analyzed using untargeted capillary electrophoresis time-of-flight mass spectrometry (CE-TOF/MS). Of the 247 metabolites detected in 19 traditional and three modernized Doenjang samples, the level of 55 metabolites were significantly different between the two production groups. The S-plot of the orthogonal projection to latent structures-discriminant analysis (OPLS-DA) revealed that nine compounds (tryptamine, 2-phenylethylamine, citrulline, gamma-aminobutyric acid, putrescine, tyramine, 2-aminoisobutyric acid, stachydrine, and N5-ethylglutamine) were highly distributed in the traditional group, and six compounds (arginine, citric acid, choline, cytidine, hypoxanthine, and glucaric acid) were considered distinguishable metabolites of the modernized group. Microbial community analysis indicated that the levels of these metabolites were significantly altered by the presence of Bacillus spp., Enterococcus faecium, Tetragenococcus halophilus, Aspergillus oryzae, Penicillium spp., and Saccharomyces cerevisiae. These findings will give better understanding of the influence of the manufacturing process on Doenjang production in terms of both microbial activity and metabolite profiles.

Stachydrine derived from fermented rice prevents diet-induced obesity by regulating adipsin and endoplasmic reticulum homeostasis.

Makgeolli, a widely consumed traditional alcoholic beverage in Korea, is brewed mainly from rice using Nuruk as a fermentation starter, which contains fungi, yeast, and lactic acid bacteria. Among 58 Makgeolli samples brewed using various Nuruks, we found that one exhibited anti-obesity properties, with stachydrine shown to be responsible for these properties. Stachydrine promotes lipolysis and inhibits lipid accumulation in 3T3-L1 adipocytes; it also reduces weight gain and improves glucose tolerance and insulin resistance in a mouse model. Stachydrine dramatically suppresses adipsin mRNA levels in liver and adipose tissue, whereas serum adipsin levels were elevated in stachydrine-treated mice compared to mice fed a high-fat diet alone. Moreover, stachydrine recovers endoplasmic reticulum homeostasis and regulates adipsin expression. We highlight the potential use of stachydrine as a therapeutic agent for the treatment of obesity and insulin resistance and the use of Makgeolli fermented by Nuruk as a source of novel bioactive compounds.

Importance of lactic acid bacteria in Asian fermented foods.

Lactic acid bacteria play important roles in various fermented foods in Asia. Besides being the main component in kimchi and other fermented foods, they are used to preserve edible food materials through fermentation of other raw-materials such as rice wine/beer, rice cakes, and fish by producing organic acids to control putrefactive microorganisms and pathogens. These bacteria also provide a selective environment favoring fermentative microorganisms and produce desirable flavors in various fermented foods. This paper discusses the role of lactic acid bacteria in various non-dairy fermented food products in Asia and their nutritional and physiological functions in the Asian diet.

Characterization, prebiotic and immune-enhancing activities of rhamnogalacturonan-I-rich polysaccharide fraction from molokhia leaves.

Plant-derived polysaccharides possess potential health benefits that improve intestinal health and the immune system. Molokhia leaves have a large amount of mucilage polysaccharide; in the present study, crude polysaccharide extract was prepared from molokhia leaves. The molecular weight of molokhia leaf polysaccharide fraction (MPF) was estimated to be 51.2 × 103 Da. Polysaccharide was methylated and the structure of MPF was mainly composed of rhamnogalacturonan-I structure with side chains, such as galactans and linear glucan (starch), as shown by GC-MS analysis. To study the biofunctional effects of MPF, its prebiotic and intestinal immune-enhancing activities were assayed in vitro. MPF exhibited good prebiotic activity, as shown by its high prebiotic scores, and increased contents of total short-chain fatty acids on five probiotic strains. In addition, MPF showed immune-enhancing activity on Peyer's patches, as revealed by the high bone marrow cell proliferating activity and production of immunoglobulin A and cytokines. These results demonstrate that MPF may be a potential beneficial prebiotic and intestinal immune-enhancer, which may have wide implications in the food industry.

Influence of aflatoxin in Nuruk on the safety of starch-based alcoholic beverage.

Nuruk is a fermentation agent used to manufacture alcoholic beverages, which contains a variety of microorganisms. Most microorganisms in Nuruk are useful for the production of alcoholic beverages; however, Nuruk can be infected with Aspergillus flavus, which produces aflatoxin (AF). Therefore, this study analyzed total AF concentrations in Nuruk, the transfer of AF from Nuruk to alcoholic beverages, and AF-producing microorganisms to determine the safety of alcoholic beverages with respect to this toxin. ELISA showed that total AF levels in 14 of 61 Nuruk samples exceeded 15 ppb, the Korean permissible level in cereal products. In alcoholic beverages produced with Nuruk containing AF levels >15 ppb, only AF G1 was detected, at a level of 0.3 ppb, and the transfer ratio of AF G1 was approximately 1.2% to 1.3%. The dominant genera in Nuruk were Aspergillus and Rhizopus. Among 30 strains belonging to Aspergillus, 10 produced only AF B1 at levels of 0.1 to 2.4 ppb after incubation at 25 °C for 8 days on potato dextrose agar plates. Although AF in Nuruk was rarely transferred to alcoholic beverages and the aflatoxigenic strains were found to possess poor AF-producing capacity, further efforts to reduce AF in Nuruk are needed to ensure the safety of alcoholic beverages.