In vitro gastric digestion and emptying of cooked white and brown rice using a dynamic human stomach system

In this study, a dynamic in vitro human stomach system was employed to elucidate the influence of structural differences between white and brown rice on gastric emptying and starch digestion. The evolution of gastric digesta particle size distribution, pH, viscosity and starch hydrolysis was investigated during digestion. Due to the protective effect of the outer bran layer against structural breakdown, brown rice showed higher pH buffering capacity, larger digesta particle size and greater rheology, resulting in a delayed gastric emptying and consequently, lower starch hydrolysis in an overall starch digestibility in the stomach than the white rice. The current study has provided quantitative evidence regarding the importance of macrostructure (i.e. the bran layer) in rice gastric digestion that may further impact intestinal absorption. Meanwhile, the particle size was significantly smaller in the digesta emptied out of the stomach in both white and brown rice throughout the digestion compared to that retained in the stomach. This demonstrates an effective size reduction and sieving efficiency exhibited by the in vitro system. It is practically meaningful to use the in vitro system to track the dynamic changes in structural and physicochemical properties of food materials during digestion in the stomach.