Background – In-vitro models of the human digestive system are useful for identifying factors that may influence the molecular behaviour of nutritional ingredients during digestion and passage into the circulatory system. It is important that models faithfully represent important digestive processes with the minimum of operational complexity. Current models (a) usually use mechanical size reduction to mimic chewing and (b) sometimes use a Caco-2 epithelial cell monolayer to estimate uptake into cells, but not to evaluate metabolism across the cell layer. Objectives – To investigate (a) whether chewing can be substituted by mechanical size reduction and (b) whether passage across Caco-2 cells can be used to assess the potential for metabolism of food components during uptake. Design – (a) Using fresh and processed fruit as example foods, the size profile and microstructure of chewed (ready to be swallowed) pieces was examined. Subsequent release of fruit sugars during simulated gastric and intestinal processing was monitored. (b) The passage of beta-carotene and catechin across a Caco-2 epithelial cell monolayer was studied.
Outcomes – (a) Physiologically, chewing cannot be simulated with simple size reduction methods because of the heterogeneity of chewed particle sizes (75 μm – 7 cm) and shapes, and the effects of oral processing on bolus characteristics. The large size (> 0.5 cm) of chewed fresh or dried fruit results in incomplete release of sugars after simulated gastric and small intestinal digestion (up to 47% lower compared with juice). (b) After 2 h assay, beta- carotene is metabolized by the Caco-2 cell monolayer more extensively (in total, approximately 8.03% conversions to retinol) than catechin (about 1.43E-5% conversion to catechin metabolites).
Conclusion – (a) Chewed particle characteristics are a likely determinant of subsequent nutrient release from solid foods and should not be overlooked in the development of in-vitro digestion models. (b) the Caco-2 cell monolayer can be used to monitor metabolic transformation of nutrients that may be relevant to first pass metabolism in-vivo.