In vitro fermentation of legume cells and components: effects of cell encapsulation and starch/protein interactions

Intact legume cotyledon cell walls (CW) hinder the access of digestive enzymes and maintain the physical integrity of cellular structures under in vitro and in vivo conditions, resulting in the transport of cellular structures and their contents from food legumes to the large intestine. The subsequent colonic fermentation of intact legume cells and polymer components is not well understood. In vitro fermentation of intact cells, broken cells, isolated starch, and cell walls from low (60 °C; LHT) and high (95 °C; HHT) heat-treated pea, and mungbean was carried out for 72 h after inoculation with mixed faeces from five pigs fed a controlled (legume-free) diet. The rate and extent of cumulative gas production, short chain fatty acid end-products, as well as alpha-amylase and protease activities, were found to be dependent on cellular integrity, botanical origin, and thermal treatment. For isolated CW and starch substrates, similar fermentation behaviour was found across the three legume types, including a decrease in starch molecular order during the fermentation process. However three different fermentation extents were observed for intact and broken cells: intact > broken for mungbean, intact ~ broken for HHT pea, and intact < broken for LHT pea. These differences can be rationalised on the basis of substrate differences in cell wall porosity and starch/protein interactions. The fermentability of processed legumes containing intact or broken cells therefore cannot be predicted from a knowledge of the fermentation behaviour of constituent starch and cell wall components and depends on both botanical origin and processing history.