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In the food industry, the competition and reciprocity between lactic acid bacteria (LAB) and yeasts in co-culture and the interactions of their metabolites affect product quality. Quorum sensing (QS) is a communication mechanism between bacterial cells, which participates in multiple physiological behaviors. The effects of Saccharomyces cerevisiae YE4 cell-free supernatant (CFS) on LAB were explored from the aspects of growth and metabolism, QS, and protein expression. The results showed the CFS inhibited not only the growth of Enterococcus faecium 8–3 and Lactobacillus fermentum 2-1 but also their acid production and biofilm formation. The acid production and biofilm amount was significantly decreased by 18.4% and 12.8% in L. fermentum 2–1 and E. faecium 8–3, respectively. The effect of CFS on QS was shown in the changes of Autoinducer-2 (AI-2) activity, luxS and pfs genes expression. Moreover, a total of 136 proteins of E. faecium 8-3 differed significantly in co-cultured with CFS, which involved in metabolic pathways including oxidative phosphorylation, pyruvate metabolism, metabolic pathways, mismatch repair, QS system, two-component system, and ABC transporters. Therefore, S. cerevisiae YE4 CFS might affect the physiological metabolism of E. faecium 8-3 by affecting the energy metabolism and QS system. • S. cerevisiae YE4 CFS influenced E. faecium and L. fermentum physiological behaviors. • S. cerevisiae YE4 CFS caused changes in AI-2 activity and QS gene expression. • YE4 CFS might achieve inhibition by affecting energy metabolism and QS system. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the effect of the signal molecule AI-2 on biofilm formation in Lactobacillus sanfranciscensis. We found that the influence of signal molecule AI-2 on strains is related to a variety of physiological metabolic behaviors, such as bacterial growth, morphological characteristics, biofilm development, related gene expression, and bile salt stress tolerance. The survival rates of planktonic and biofilm forms of L. sanfranciscensis were measured after acid, bile salt, and in vitro digestion. The results showed that the biofilm strain had stronger stress resistance. Next, the effects of endogenous and synthetic AI-2 on L. sanfranciscensis growth were compared. The addition of synthetic AI-2 improved L. sanfranciscensis cell density and enhanced bacterial cohesion. Upregulated expression of ftsH was found to promote biofilm formation and growth. AI-2 intervention will improve bile salt tolerance in L. sanfranciscensis. In conclusion, the signal molecule AI-2 is involved in the regulation of biofilm formation and development in L. sanfranciscensis. • The biofilm of Lactobacillus sanfranciscensis had stronger stress resistance. • Effect of endogenous AI-2 on the growth and biofilm was studied for the first time. • The synthetic AI-2 increased the biofilm formation and enhanced bacterial cohesion. • AI-2 intervention will improve bile salt tolerance in L. sanfranciscensis. [ABSTRACT FROM AUTHOR]

As a recognized safe starter, lactic acid bacteria can improve the quality characteristics of fermented sausages and ensure the safety characteristics of sausages to a certain extent. The purpose of this study was to analyze the effects of Lactobacillus helveticus IMAUJBH1 on lipid profiles and volatile flavor compounds of Inner Mongolia mutton fermented sausage by lipidomics and GC-MS. The results showed that a total of 2024 lipid molecules were identified, and 1135 differential lipids were screened by multivariate analysis (P < 0.05, VIP>1). Pathway topology analysis showed that glycerophospholipid metabolism, glyceride metabolism and sphingolipid metabolism pathways were the three most active pathways. Furthermore, 21 key differential lipid molecules and 5 key volatile flavor compounds were selected as characteristic substances for correlation analysis. The results of correlation study indicated that the addition of Lactobacillus helveticus IMAUJBH1 would further affect the flavor of fermented mutton sausage by affecting the relative expression of lipid molecules LPC (17:0), LPC (22:6), LPC (18:1), LPC (18:3), LPC (22:4), Cer (d18:1/16:0), and Cer (d18: 1/22:0). The results provide a scientific theoretical basis for the application of IMAUJBH1 in mutton fermented sausage, and further promote the development of mutton processing industry in Inner Mongolia. • Lipidomics was used to evaluate the lipid metabolism of fermented sausages. • 21 Key differential lipid molecules were identified as characteristic substances. • 5 key volatile flavor substances (OAV>1) were used as characteristic substances. • IMAUJBH1 can reduce the content of related aldehydes and esters. [ABSTRACT FROM AUTHOR]

To explore the effects of different quorum sensing inhibitors (QSIs) on the biofilm formation of Lactobacillus fermentum , a high-production signal molecule AI-2 screened by the research group, was taken as the research object and subjected to various QSIs. Three QSIs, namely 100 μmol/L d -galactose, 200 μmol/L d -ribose, and furanone, could inhibit the AI-2 activity of L. fermentum and the biofilm formation in a certain concentration range but not significantly affect the growth of the strain. Scanning electron microscopy and fluorescence microscopy revealed that each QSI did not significantly affect the bacterial cell morphology in planktonic and biofilm states at the optimal inhibitory final concentration, although they reduced the adhesion of the strain. The expression of luxS , a key gene of quorum sensing, was downregulated. When biofilm production increased, QSIs were added, and the activity of the AI-2 was consistent with the change in biofilm production. Whole-genome technology revealed that QSIs inhibited the expression of the luxS , resulting in restriction of pyruvate synthesis and downregulation of the expression of genes such as gapA , pgmB , ribBA , and ribF , which in turn affected the transport and metabolism of carbohydrates and coenzymes in the strain and ultimately reduced the biofilm formation of L. fermentum. • The signal molecule AI-2 of Lactobacillus fermentum does not depend on cell density. • The effect of quorum sensing inhibitors on L. fermentum biofilm is strain-specific. • Different QSIs reduce biofilm formation by interfering with the transduction of AI-2. • QSIs may affect the transport and metabolism of carbohydrates and coenzymes in cell. [ABSTRACT FROM AUTHOR]

Increasingly attention has been paid to the active substances in grapefruit peel. In this study, insoluble bound phenolic compounds (BP) were released from grapefruit peel insoluble dietary fiber (GP-IDF) by microwave extraction (M-BP), enzymatic hydrolysis (E-BP) and combined microwave and enzymatic treatment (ME-BP). The results showed that the yield of ME-BP was the highest (148.856 ± 0.620 GAE mg/100 g), and conditions of microwave treatment (microwave power, temperature, time) were 600 W, 85 °C, and 37 min, while that of enzymatic treatment were 8% addition, 60 °C, and 2 h. Scanning electron microscopy displayed that GP-IDF became looser by ME. ME mainly resulted in the removal of lignin in IDF from X-ray diffraction, which was consistent with FT-IR. Twenty seven BP were identified by UPLC-ESI-QTOF-MS/MS. The high content of gallic acid (42.50 ± 3.21 μg/g DW), ferulic acid (18.46 ± 1.65 μg/g DW) and protocatechuic acid (6.16 ± 0.72 μg/g DW) was quantified by LC-ESI-QqQ-MS/MS. Furthermore, ME-BP showed stronger antioxidant capacities than that of others (ABTS, oxygen and DPPH free radical scavenging ability), and showed good inhibition of α-glucosidase. Our results demonstrated that combined microwave and enzymatic treatment was an effective treatment for improving the release of BP. • Combined microwave and enzymatic treatment (ME) released bound phenolic compounds. • Optimal condition was 600 W, 85 °C for 37 min and 8% enzyme dosage, 60 °C for 2 h. • ME-IDF (insoluble dietary fiber) was more seriously disintegrated than others. • Composition and content of ME-BP (bound phenolic compounds) was analyzed. • ME-BP exhibited higher antioxidant capacities and α-glucosidase inhibition. [ABSTRACT FROM AUTHOR]