Advanced near-real dynamic in vitro human stomach system for investigating gastric digestion and emptying of cooked black rice with gradient milling

The in vitro dynamic gastric digestion and emptying characteristics of black rice bolus with different milling degree were determined by the near-real dynamic in vitro human stomach (DHS-IV). The gastric retention rate for 120 min of in vitro gastric digestion ( GR 120 ) showed a decreasing trend (43.15%–25.66%) with the increase of milling degree, and the half-life of gastric emptying ( t 1/2 ) in DHS-IV for whole grain, lightly milled black rice and refined black rice were 78.36, 79.64 and 62.83 min, respectively. The contents of total phenols and total flavonoids exhibited the increased trend in DHS-IV compared to those in oral stage of digestion. The viscosity of the emptied liquid digesta fractions (the apparent viscosity at a shear rate of 50 s -1 (η 50 : 0.001–0.041 Pa·s)) increased with the prolonged time of gastric emptying in vitro . Correlation analysis further demonstrated that changes in the content of insoluble solids (mainly gelatinous substances) were the main reason for the viscosity changes in the liquid digesta fractions. This study revealed that whole-grain and lightly milled black rice showed good potential related to postprandial satiety and glucose release. • The pH changing patterns in the DHS-IV from 0 to 120 min were in accordance with the human stomach. • The DHS-IV system showed the "sieving effect" for the solid fractions of black rice digesta. • Whole and lightly milled black rice exhibited the delayed gastric emptying. • The variations in insoluble solid content were the contributors to changes in digesta viscosity.