Dairy products, due to manufacturing processes, exhibit an array of possible structures at different length scales and are associated with beneficial nutritional and health effects. However, to date there is very little mechanistic understanding of such links. Unravelling the fate of food in the gastrointestinal tract is essential to better understand the health effects of food.
The investigation of different dairy structured matrices was performed using a semi-dynamic model of gastric digestion, developed in this thesis, to simulate the main dynamics of the adult stomach, i.e. gradual gastric acidification, fluid secretion and emptying. It was validated with two dairy matrices obtaining a similar gastric behaviour compared to the corresponding in vivo digestion.
The ‘fast’ and ‘slow’ digestion kinetics of whey proteins and caseins were shown to be due to their behaviour in the stomach, presenting soluble aggregates and solid, firm coagulation, respectively, which was linked to a higher ex vivo Leu absorption at early and late stages of digestion. The gastric restructuring of caseins was modulated by changing the whey protein to casein ratio, addition of lipid, and processing by heating and homogenisation. The most intensive processing resulted in weaker, fragmented coagulation, leading to quicker kinetics of nutrient emptying and rapid protein hydrolysis. The latter was linked to an easier access of pepsin into the weaker structure. The modulation of nutrient digestion kinetics was also obtained by comparing specific dairy macrostructures of semi-solid versus liquid through different gastric behaviours, which could be linked to the satiety responses observed in vivo.
This thesis clearly demonstrated the key role of the gastric phase on nutrient bioaccessibility, which can be associated to physiological responses of dairy products. The modulation of gastric behaviour should be further studied and can be exploited to develop food structures with improved and/or tailored biofunctional properties addressing health/nutritional requirements
