Digestive dynamics of yoghurt structure impacting the release and bioaccessibility of the flavonoid rutin

Rutin is a dietary flavonoid and a potent antioxidant with clinically relevant functions. Hence, rutin-enriched food products can be used as functional foods. However, rutin has low bioavailability because of its low water solubility, poor stability and limited membrane permeability. We previously reported a casein-rutin co-precipitate that significantly increased water solubility, compared with commercially available rutin powders. This work investigated the gastrointestinal behaviour of a yoghurt enriched with casein-rutin co-precipitate (RuYO) and an unfortified yoghurt combined with powdered rutin in a vegetable-based capsule (CtYO + Ru). A semi-dynamic in vitro digestion protocol was followed; the gastric phase was simulated in a human gastric simulator. The physical properties and rutin content of digesta samples were determined at different digestion times. The solids retention of RuYO and CtYO + Ru in the gastric phase decreased with increasing digestion time, confirming that gastric emptying occurred at a constant rate. Confocal microscopy indicated that the protein network was increasingly hydrolysed during gastric digestion. The release and stability of rutin during the digestion of RuYO were dramatically different from those of CtYO + Ru. Although a significant amount of the flavonoid remained in the insoluble fraction during gastric digestion, it was more stable in RuYO than in CtYO + Ru (total cumulative recoveries of 98% and 61% respectively). Similarly, rutin degradation was lower in RuYO in the intestinal phase (total cumulative recovery: RuYO, 26%; CtYO Ru, 17%). Overall, yoghurt fortified with rutin-casein co-precipitate gives better in vitro rutin bioaccessibility than the same yoghurt co-digested with a rutin supplement capsule.