Factors affecting plant food particle behaviour during in vitro colonic microbial fermentation

Dietary fibre (DF) plays an important role in maintaining human health, partly mediated by the gut microbiota and their responses. Diverse plant foods are the main source of DF in human diets, which generally reach the colon in particulate form. Factors such as botanical origin and particle size influence the physicochemical and digestive properties of these particles and are also likely to impact ( in vitro ) colonic fermentation. This review examines the identified effects of botanical origin and particle size of different plant foods on human colonic microbial responses in vitro . It highlights how variations in the microstructure and chemical composition of representative examples from cereals, legumes, nuts, fruits and vegetables influence colonic microbial fermentation. The functional pathways of human colonic microbes involved in degrading these plant foods are identified, providing insights into the connection between plant food characteristics and microbial responses. The combined effects of botanical origin and particle size determine the in vitro colonic fermentability of plant foods. Gut microbial responses are linked to specific plant cell wall structures and the nutrients they encapsulate, which interact with substrate-degrading microbes. Size reduction of plant food particles can effectively modify microbial responses, and water-holding capacity is identified as a potentially important functional factor. A better understanding of these interactions is critical for defining and optimising the nutritional value of plant foods in the human gut, as well as identifying opportunities for innovative food products that target gut microbiota responses. • Plant food colonic fermentation is influenced by both particle size and chemical composition. • Particle size influences fermentation outcomes for compact more than expanded microstructures. • Starch, protein and lipids trapped in plant cell structures contribute to fermentation outcomes. • Food formulation with selected plant particles could target desirable gut fermentation effects.