Retention of intact plant cells to the end of the small intestine leads to transport of entrapped macronutrients such as starch and protein for colonic microbial fermentation, and is a promising mechanism to increase the content of resistant starch in diets. However, the effect of gastro-intestinal bio-mechanical processing on the intactness of plant cells and the subsequent resistance to enzymatic digestion of intracellular starch and protein are not well understood. In this study, intact cells isolated from legume cotyledons are digested in a laboratory model which mimics the mechanical and biochemical conditions of the rat stomach and duodenum. The resulting digesta are characterised in terms of cell (wall) integrity as well as intracellular starch and protein hydrolysis. The cells remained essentially intact in the model with negligible (ca. 2–3%) starch or protein digestion; however when the cells were mechanically broken and digested in the model, the hydrolysis was increased to 45–50% suggesting that intact cellular structures could survive the mixing regimes in the model stomach and duodenum sufficiently to prevent digestive enzyme access. Apart from intact cell walls providing effective barrier properties, they also limit digestibility by restricting starch gelatinisation during cooking, and significant non-specific binding of α-amylase is observed to both intact and broken cell wall components, providing a third mechanism hindering starch hydrolysis. The study suggests that the preservation of intactness of plant cells, such as from legumes, could be a viable approach to achieve the targeted delivery of resistant starch to the colon.

A near real dynamic in vitro human stomach (new DIVHS) system has recently been advanced in this study, based on the previous rope-driven in vitro human stomach model (RD-IV-HSM). The new DIVHS mainly consists of a J-shaped silicone human stomach model fabricated using 3D-printing technology which has a similar stomach morphology, dimension and wrinkled inner structure to those present in vivo, and an electromechanical instrument composed of a series of motors, rollers and eccentric wheels to produce peristaltic contractions. The simulated stomach system was able to generate consistent gastric emptying ratios of both the solid and liquid fractions in beef stew mixed with orange juice with that reported in vivo (p > 0.05). By fitting the gastric retention data with a modified power-exponential model, the solid fractions showed an average emptying half-time (t_1/2) of 74.1 min and a lag phase (t_lag) of 36.3 min in the new DIVHS, similar to that obtained in vivo where the average values of t_1/2 and t_lag were 75.8 min and 40.2 min, respectively. The performance of the new DIVHS was further validated by showing good qualitative matches of the gastric pH, particle size distribution and emptying profiles of cooked rice with the literature in vivo data. These results indicate that it is a reasonable approach to perform in vitro gastric digestion experiments using the new DIVHS, which is practically meaningful.