Evolutions of rheology, microstructure and digestibility of parboiled rice during simulated semi-dynamic gastrointestinal digestion

ABSTRACT Despite the general recognition about the beneficial effects of parboiled rice in lowering glycemic response, there are contradictory studies regarding the negligible effect of parboiling treatment on digestive behaviour of rice and its glycemic index (GI) value. In this study, the rheology, microstructure, particle size distribution, and starch hydrolysis before and within semi-dynamic in vitro gastrointestinal digestion were measured and compared between the cooked parboiled and non-parboiled (control) rice. The protein content was significantly increased from 4.04 to 5.26 g/100 g, while the fat and moisture contents were slightly decreased after parboiling. The apparent viscosity and moduli of parboiled rice were higher than that of the control rice before and during the in vitro digestive phases. Optical and confocal microstructures showed denser gel-networks with less disrupted granules or clusters in the parboiled rice during digestion. At the end of digestion, parboiled rice had a starch digestibility of around 74 g/100 g whereas it was 85 g/100 g for the control. The reduced starch digestibility of parboiled rice was supported by its higher digesta rheology and more compact microstructure during digestion. This work suggests that parboiling is a promising and practical approach to producing healthier cooked rice with lower starch digestibility.