Jie Luo

Ultrasound-assisted fermentation (UAF) was evaluated as a calorimetrically calibrated strategy for biotransforming Astragalus membranaceus isoflavones using Lactiplantibacillus plantarum. Water-based calorimetry yielded power-density estimates of 46.51 ± 4.03 and 86.05 ± 4.03 W/L for the fermentation vessel configuration. High-dose UAF accelerated the conversion of isoflavone glucosides into calycosin and formononetin, reaching 99.7 ± 2.4% of the conventional 24 h aglycone level by 18 h with a 50% higher mean formation rate over 10–18 h. No aglycone formation was detected in the sterile ultrasound control under the tested conditions. At the 18 h time-matched sampling point, high-dose UAF yielded higher in vitro antioxidant capacities, stronger DPP-IV and pancreatic lipase inhibition, and greater measured intestinal-phase calycosin recovery (374.80 vs. 314.31 μg/g) than conventional fermentation. At 16 h, extracellular β-glucosidase activity increased dose-dependently from 3.52 ± 0.82 to 11.19 ± 0.45 U/mL (conventional vs. high-dose UAF), whereas intracellular activity remained comparable across treatments. Combined with qualitative SEM and CLSM observations, these findings are consistent with enhanced extracellular enzyme availability and plant matrix disruption, without establishing de novo enzyme synthesis or a specific permeabilisation mechanism.

Lactic acid bacteria exopolysaccharides (LAB EPS) have garnered significant interest owing to their beneficial biological properties and safety. This study aimed to screen LAB EPS with comprehensive biological activities and anti-allergic potential from four high-yield strains, isolate and characterize their homogeneous polysaccharide fractions, and preliminarily explore their anti-allergic mechanism. Through in vitro evaluation of antibacterial, hyaluronidase inhibitory, antioxidant and immunomodulatory activities, Lacticaseibacillus casei LZ9183 EPS (183 EPS) was identified as the optimal candidate with the most superior comprehensive performance. Further purification via DEAE-52 anion exchange chromatography and Sephadex G-100 gel filtration chromatography yielded two homogeneous polysaccharide fractions, LZEPS-1 and LZEPS-2. Structural characterization results showed that LZEPS-1 (28.73 kDa) was a neutral polysaccharide composed of rhamnose, galactose, glucose and mannose with a total sugar content of 94.39 ± 0.92%, while LZEPS-2 (95.58 kDa) was an acidic polysaccharide containing glucose, galactose, arabinose, mannose, xylose and glucuronic acid with 92.17 ± 1.22% total sugars and 1.72 ± 0.04% protein. Using the RBL-2H3 cell degranulation model, we demonstrated that 183 EPS, LZEPS-1 and LZEPS-2 effectively alleviated IgE-mediated allergic responses by inhibiting the release of β-hexosaminidase and histamine, and modulating the secretion of IL-4 and TNF-α to restore the Th1/Th2 balance. These results propose that LAB EPS could potentially be utilized as natural anti-allergic functional ingredients in the development of functional foods or dietary supplements.

Xiangxi radish paocai is a regionally distinctive fermented vegetable whose characteristic aroma depends on microbial succession during brine fermentation, but the active microbial and metabolic basis of this flavor remains unclear. Here, metatranscriptomics, metabolomics, and HS-SPME-GC-Q-TOF-MS were integrated to characterize flavor formation during Xiangxi radish paocai fermentation. Organic acid accumulation, especially lactic and acetic acid, together with free sugar depletion, represented the main environmental pressure associated with microbial succession (R2 > 0.79). This shift favored acid-tolerant bacteria, with active Levilactobacillus namurensis becoming dominant and increasing from 41.01% to 47.18%. HS-SPME-GC-Q-TOF-MS identified 24 key aroma-active compounds, including the novel meat flavour compound 2-pentylpyridine, which showed a relative odour activity value as high as 2700.02. Correlation analysis further showed that L. namurensis abundance was strongly correlated with 16 characteristic aroma compounds, likely linked to precursor metabolism involving serine, alanine, glycine and histidine. These findings provide a mechanistic basis for understanding flavor development in Xiangxi radish paocai and support for optimization of the fermentation process.

Lactic acid bacteria exopolysaccharides (LAB EPS) have garnered significant interest owing to their beneficial biological properties and safety. This study aimed to screen LAB EPS with comprehensive biological activities and anti-allergic potential from four high-yield strains, isolate and characterize their homogeneous polysaccharide fractions, and preliminarily explore their anti-allergic mechanism. Through in vitro evaluation of antibacterial, hyaluronidase inhibitory, antioxidant and immunomodulatory activities, Lacticaseibacillus casei LZ9183 EPS (183 EPS) was identified as the optimal candidate with the most superior comprehensive performance. Further purification via DEAE-52 anion exchange chromatography and Sephadex G-100 gel filtration chromatography yielded two homogeneous polysaccharide fractions, LZEPS-1 and LZEPS-2. Structural characterization results showed that LZEPS-1 (28.73 kDa) was a neutral polysaccharide composed of rhamnose, galactose, glucose and mannose with a total sugar content of 94.39±0.92%, while LZEPS-2 (95.58 kDa) was an acidic polysaccharide containing glucose, galactose, arabinose, mannose, xylose and glucuronic acid with 92.17±1.22% total sugars and 1.72±0.04% protein. Using the RBL-2H3 cell degranulation model, we demonstrated that 183 EPS, LZEPS-1 and LZEPS-2 effectively alleviated IgE-mediated allergic responses by inhibiting the release of β-hexosaminidase and histamine, and modulating the secretion of IL-4 and TNF-α to restore the Th1/Th2 balance. These results propose that LAB EPS could be potentially utilized as natural anti-allergic functional ingredients in the development of functional foods or dietary supplements.

Interactions mediated by quorum sensing critically influence metabolic coordination in lactic acid bacterial fermentations, yet the extent to which exogenous signaling molecules modulate flavor formation remains insufficiently defined. Here, a binary yogurt fermentation model comprising Levilactobacillus brevis 54 and Lacticaseibacillus casei 56 was employed to elucidate how externally supplied autoinducing peptides (AIP) and autoinducer-2 (AI-2) reprogram microbial behavior and flavor-associated metabolism. Targeted supplementation with strain-specific AIP (AGQYYINHR and AYFQT) significantly enhanced bacterial growth, with elevated viable cell counts closely associated with accelerated casein hydrolysis and increased accumulation of AA-derived metabolites. In parallel, exogenous AI-2 (24 μM) stimulated bacterial growth and activated the AI-2/LuxS signaling cascade, accompanied by increased transcription of luxS, plnB, and plnC. Metabolomic analyses revealed that AIP primarily modulated AA metabolic pathways, whereas AI-2 exerted broader regulatory effects spanning AA, carbohydrate, and central carbon metabolism, partly mediated through upregulation of the AI-2-associated enzyme MtnN. Integrated profiling of nonvolatile and volatile flavor compounds demonstrated that coordinated AIP- and AI-2-mediated signaling redirected metabolic fluxes toward flavor-active derivatives, leading to enhanced formation of alcohols, ketones, and organic acids that contribute to yogurt aroma. Collectively, this study delineates how parallel intraspecies and interspecies quorum-sensing pathways integrate to reshape metabolic networks during yogurt fermentation, providing mechanistic insight into signal-driven flavor modulation and a framework for the rational design of flavor-enhanced fermented dairy systems.