Whole-grain foods have attracted emerging attention due to their health benefits. Whole grains are rich in bound polyphenols (BPs) linked with dietary fibers, which is largely underestimated compared with free polyphenols. In this study, in vitro simulated gastrointestinal digestion and colonic fermentation models were used to study the release profile and metabolism of BPs of oat bran. Significantly higher level of BPs was released during in vitro colon fermentation (3.05 mg GAE/g) than in gastrointestinal digestion (0.54 mg GAE/g). Five polyphenols were detected via LC-MS and their possible conversion pathways were speculated. Released BPs exhibited chemical antioxidant capacity. 16S rRNA sequencing further revealed that Clostridium butyricum, Enterococcus faecalis, Bacteroides acidifaciens were the key bacteria involved in the release of BPs, and this was verified by whole-cell transformation. Our results helped to explain the possible mechanism of the health benefits of BPs in whole grains.

This study provides different opinion for exploring the mechanism of catechin (CAT) relieving nonalcoholic steatohepatitis (NASH), it is more innovative to explore from the perspective of intestinal microorganism. Through in vitro fermentation experiments, CAT could improve the abundance of Enterococcus, and Enterococcus faecalis (EF) accounts for the vast majority of Enterococcus in human gut. The experimental results in vivo showed that EF group and CAT+EF group could reduce the body weight, liver weight and epididymal fat weight of NASH mice, and improve the changes of serum and liver indexes. HE staining observation showed that these two groups have greatly improved the fatty degeneration, balloon degeneration and necrotic focus caused by NASH. The alleviation of CAT+EF group was more obvious. Results of targeted metabonomics showed that CAT could promote EF to produce more methyl palmitate (MP, C16:0), which plays a great role in relieving NASH. Our results indicated that EF could alleviate NASH and CAT+EF group had better alleviation may due to more production of MP by EF. This study provides a new idea for CAT to alleviate NASH.

Oat avenanthramides (AVNs) have been found to exhibit novel lipid-lowering effects. However, the mechanism remains unclear. In this study, the effect of avenanthramide B (AVN B), as one of the major AVNs, on high-fat diet (HFD)-induced mice was investigated. Results showed that AVN B significantly inhibited weight gain and improved hepatic and serum lipid biochemical indices. Hepatic RNA-Sequencing analysis suggested that AVN B significantly modulates fatty acid (FA) metabolism. Hepatic real-time qualitative polymerase chain reaction (RT-qPCR) and Western blot results indicated that AVN B could alleviate FA synthesis by activating the AMPK- SREBP1c-FAS, and increase FA oxidation by activating the AMPK/CPT1A and PPARα. Additionally, AVN B had a regulating effect on ileum lipid metabolism by inhibiting intestinal cell differentiation and down-regulating the expression levels of FA absorption-related protein and gene. Moreover, AVN B promoted the growth of beneficial bacteria and fungi such as Coriobacteriaceae_UCG-002, Parvibacter, Enterococcus, and Aspergillus, while decreasing the abundance of Roseburia, unclassified_f_Lachnospiraceae Cladosporium, Eurotium, unclassified_f_Aspergillaceae and unclassified_f_Ceratocystidaceae. All these results provided new points of the lipid-lowing mechanism of AVNs and oats via the gut-liver axis.

Fermentation substrates of rice with different milling degrees (MDs) were prepared and fermented with human feces to compare their fermentation properties and effects on gut microbiota. MD 0s, MD 5s and MD 60s represented brown rice, moderately-milled rice and white rice, respectively. After in vitro fermentation, the MD 5s group showed higher starch utilization, compared with the MD 0s and 60s groups evaluated by Fourier transform infrared spectrometer, and confocal laser scanning microscope. Effects of fermentation substrates of rice with different MDs on gut microbiota were evaluated by 16S rDNA sequencing. All the sample groups reduced the pH and produced short-chain fatty acids (SCFAs) and branched-chain fatty acids. The MD 5s group exhibited higher α-diversity than the MD 0s and 60s groups. Abundances of Phascolarctobacterium, Blautia and norank_f_Ruminococcaceae were higher in the MD 0s and 5s groups, compared with the MD 60s group. These bacteria were also positively correlated with the SCFAs production via Spearman correlation analysis. In vitro culture assay revealed that fermentation substrates of MD 0s and 5s promoted the growth of two probiotics (Akkermansia muciniphila and Bifidobacterium adolescentis). Our results showed that moderate milling might be an appropriate way to produce rice products with richer nutrients and better fermentation properties.