Transcriptome analysis revealing the mechanism of soybean protein isolates and soybean peptides on Lacticaseibacillus rhamnosus Lra05

Transcriptome Analysis Reveals the Role of Sucrose in the Production of Latilactobacillus sakei L3 Exopolysaccharide

Latilactobacillus (L.) sakei is a species of lactic acid bacteria (LAB) mostly studied according to its application in food fermentation. Previously, L. sakei L3 was isolated by our laboratory and possessed the capability of high exopolysaccharide (EPS) yield during sucrose-added fermentation. However, the understanding of sucrose promoting EPS production is still limited. Here, we analyzed the growth characteristics of L. sakei L3 and alterations of its transcriptional profiles during sucrose-added fermentation. The results showed that L. sakei L3 could survive between pH 4.0 and pH 9.0, tolerant to NaCl (<10%, w/v) and urea (<6%, w/v). Meanwhile, transcriptomic analysis showed that a total of 426 differentially expressed genes and eight non-coding RNAs were identified. Genes associated with sucrose metabolism were significantly induced, so L. sakei L3 increased the utilization of sucrose to produce EPS, while genes related to uridine monophosphate (UMP), fatty acids and folate synthetic pathways were significantly inhibited, indicating that L. sakei L3 decreased self-growth, substance and energy metabolism to satisfy EPS production. Overall, transcriptome analysis provided valuable insights into the mechanisms by which L. sakei L3 utilizes sucrose for EPS biosynthesis. The study provided a theoretical foundation for the further application of functional EPS in the food industry.

The investigation of soybean protein isolates and soybean peptides assisting Lactobacillus plantarum K25 to inhibit Escherichia coli

Soybean protein isolates and their hydrolysates are considered as one of the most high-quality proteins among plant proteins, and current research has shown that they have potential probiotic functions. The purpose of this study was to investigate the effects of digested soybean protein isolates (dSPI) and digested soybean peptides (dPEP) on L. plantarum K25 alone and the two bacteria when co-cultured with E. coli. It showed that dSPI and dPEP promoted the growth and metabolism of L. plantarum K25, and dSPI had a better effect. Besides, dSPI and dPEP still promoted the growth and organic acid secretion of L. plantarum K25 when co-cultured with E. coli, and the dPEP treatment was more effective than dSPI. Moreover, dSPI and dPEP reduced the survival rate of E. coli when co-cultured with L. plantarum K25. These results to some extent explained the cooperation of dSPI and dPEP with L. plantarum K25 to produce acid thereby weaken the growth of E. coli.

Can proteins, protein hydrolysates and peptides cooperate with probiotics to inhibit pathogens?

Studies have shown that probiotics can effectively inhibit pathogens in the presence of proteins, protein hydrolysates and peptides (protein derivates). However, it is still unclear the modes of probiotics to inhibit pathogens regulated by protein derivates. Therefore, we summarized the possible effects of protein derivates from different sources on probiotics and pathogens. There is abundant evidence that proteins and peptides from different sources can significantly promote the proliferation of probiotics and increase their secretion of antibacterial substances. Such proteins and peptides can also stimulate the adhesion of probiotics to intestinal epithelial cells and contribute to regulating intestinal immunity, but they seem to have the negative effects on pathogens. Moreover, a direct effect of proteins on intestinal cells is summarized. Whether or not they can cooperate with probiotics to inhibit pathogens using above possible mechanisms were discussed. Furthermore, there seems to be no consistent conclusions that protein derivates have synergistic effects with probiotics, and there is still limited evidence on the inhibiting patterns. Therefore, the existing problems and shortcomings are noted, and future research direction is proposed.

Auricularia auricula Peptides Nutritional Supplementation Delays H2O2-Induced Senescence of HepG2 Cells by Modulation of MAPK/NF-κB Signaling Pathways

Auricularia auricula is a traditional medicinal and edible mushroom with anti-aging effects. Many studies focused on polysaccharides and melanin. However, the anti-aging effects and mechanism of the nutritional supplementation of Auricularia auricula peptides (AAPs) were not elucidated. In this study, AAPs were prepared by enzymolysis of flavor protease and the protective effects on H2O2-induced senescence of HepG2 cells were explored for the first time. The potential mechanism was also investigated. AAPs were mostly composed of low molecular weights with less than 1000 Da accounting for about 79.17%, and contained comprehensive amino acids nutritionally, including seven essential amino acids, aromatic, acidic, and basic amino acids. AAPs nutritional supplementation could significantly decrease the levels of intracellular reactive oxygen species (ROS) and malondialdehyde (MDA), and increase the activities of antioxidant enzymes (SOD, CAT, and GSH-Px). In addition, the senescence-associated-β-galactosidase (SA-β-gal) activity was restrained, and the expression levels of senescence-associated secretory phenotype (SASP) (IL-6, IL-8, IL-1β, and CXCL2) were also decreased. Ribonucleic acid sequencing (RNA-Seq) was carried out to screen the differentially expressed genes (DEGs) between different groups. GO and KEGG enrichment analysis showed that the mechanism was related to the MAPK/NF-κB signaling pathways. Quantitative real-time PCR (qRT-PCR) analysis and Western blot were carried out to verify the key genes and proteins in the pathways, respectively. AAPs nutritional supplementation resulted a significant down-regulation in key the genes c-fos and c-jun and up-regulation in DUSP1 of the MAPK signaling pathway, and down-regulation in the key genes CXCL2 and IL-8 of the NF-κB signaling pathway. The results of Western blot demonstrate that AAPs nutritional supplementation could inhibit MAPK/NF-κB pathways by reducing the expression levels of IKK, IκB, P65, and phosphorylation of ERK, thus decreasing the inflammatory reaction and delaying cell senescence. It is the first time that AAPs nutritional supplementation was proved to have protective effects on H2O2-induced oxidative damage in HepG2 cells. These results implicate that dietary AAPs could be used as nutrients to reduce the development or severity of aging.

Identification and characterization of soybean peptides and their fractions used by Lacticaseibacillus rhamnosus Lra05

Soybean peptides were reported to promote the growth and metabolism of Lacticaseibacillus rhamnosus (L. rhamnosus) Lra05. However, the relationship between L. rhamnosus Lra05 and the characteristics of soybean peptides is still unclear. Therefore, digested soybean peptides (dPEP) after 36 h utilization by L. rhamnosus Lra05 were identified and analyzed. We found that L. rhamnosus Lra05 tends to utilize hydrophobic peptides with three to five amino acids residues, and hydrophilic peptides with more than five residues. They also prefer peptides with proline at penultimate C-terminal position or arginine at ultimate C-terminal position. Moreover, fraction 1 (F1) and fraction 7 (F7) acquired from dPEP using RP-HPLC exhibited the strongest growth and metabolism promoting effects, and the utilized characteristics of F1 and F7 were similar with those of dPEP. These results explained why soybean peptides could promote L. rhamnosus to some extent and strengthen theoretical basis for the application of soybean peptides as potential prebiotics.