Structure–function studies of chickpea and durum wheat uncover mechanisms by which cell wall properties influence starch bioaccessibility

Positive health effects of dietary fibre have been established; however, the underpinning mechanisms are not well understood. Plant cell walls are the predominant source of fibre in the diet. They encapsulate intracellular starch and delay digestive enzyme ingress, but food processing can disrupt their structure. Here, we compare the digestion kinetics of chickpea (cotyledon) and durum wheat (endosperm), which have contrasting cell wall structures (type I and II, respectively), to investigate a cell wall barrier mechanism that may underpin the health effects of dietary fibre. Using in vitro models, including the dynamic gastric model, to simulate human digestion, together with microscopy, we show that starch bioaccessibility is limited from intact plant cells and that processing treatments can have different effects on cell integrity and digestion kinetics when applied to tissues with contrasting cell wall properties. This new understanding of dietary fibre structure is important for effective fibre supplementation to benefit human health. Starch bioaccessibility is limited by an intact cell wall. Type 1 and type 2 cell walls, exemplified by chickpea and durum wheat, confer variable dimensions of cell integrity, digestion kinetics and starch bioaccessibility to unprocessed and processed foods. Tissue fracture properties and cell wall permeability emerge here as mechanisms by which dietary fibre affects starch bioaccessibility.