Effects of processed oats and pinto beans on the composition of human gut microbiome: An in vitro study

Oats and pinto beans, which are rich in dietary fibers and plant proteins, are two common ingredients for many processed food products, such as puffed snacks and canned foods. The objective of this study was to investigate the gut microbiome response to processed oats and pinto beans food products. Raw oats and pinto beans were canned, boiled, and extruded at selected temperatures to simulate the commercial food processing practices. The processed oat and pinto bean samples were digested in an in vitro digestion system, and were subjected to in vitro fermentation by gut bacteria from human feces, which simulated the reactions between the undigested food components and the gut microbiome. The resulting metabolites were quantitatively and qualitatively measured, the compositions of the gut microbiome were determined by 16S rRNA sequencing, and the microbiota were classified and clustered based on their amplicon sequence variants (ASVs) and co-abundancies. The results showed that pinto beans generated more gas and short-chain fatty acids (SCFA) than oats. Boiled oats had a good retention of non-digestible fermentable contents (NDFCs) for the gut microbiota to act on, resulting in greater gas and acid production than other processed oat samples. However, for processed pinto beans, high-temperature extrusion and canning resulted in more NDFCs through starch gelatinization and retrogradation. Guild-based analysis was applied to microbiome analysis to identify key bacteria contributing to microbial shift. Bacteria such as Escherichia-Shigella, Streptococcus, Anaerostipes were promoted in extruded oats, while Lachnospiraceae, Eubacterium hallii, Butyricicoccus were significantly promoted in boiled and low-temperature extruded pinto beans.