Meta-analysis of retrogradation effect on starches of white rice, and comparative study of different cooking oils and cooking methods on in vitro glucose release from white rice

Abstract

Cooling is a technique employed to reduce the high glucose release from white rice by altering the proportion of rapidly digestible (RDS), slowly digestible (SDS), and resistant (RS) starches. Retrogradation of the gelatinised starches to a crystalline structure increases the RS content that does not spike blood glucose on consumption. The meta-analysis showed that following different retrogradation durations, there were significant mean differences (MD), viz. an increase in RS (MD: 4.17 g/100 g, p < 0.00001) and decrease in RDS (MD: -7.09 g/100 g, p < 0.0001). The addition of cooking oil to rice retards the release of glucose due to the formation of an amylose-lipid complex (ALC), and together with retrogradation, further lowers glucose release. In the present work, palm oil (PO) and coconut oil (CO) were added to steamed rice by three methods: (A) stir-frying raw rice with oil before steaming, (B) adding oil in cooking water during steaming, and (C): stir-frying the steamed rice with oil, following by refrigeration at 4°C for 12 h. For nutritional composition, the moisture, fat, and carbohydrate contents of white rice were affected upon treatments. Besides, oil-treated rice released glucose slower than control in the in vitro digestibility test, showing increased RS and decreased RDS. Moreover, rice with CO added by Method A might serve as a potential prebiotic as it increased the growth of Lacticaseibacillus casei and Lacticaseibacillus rhamnosus in tandem with the decrease in oligosaccharides over 24 h. Coconut oil was the better cooking oil for reducing glucose release from white rice due to its greater ability to form ALC. The addition of CO via Method C is recommended as the lower moisture content in the rice aided formation of perfectly crystalline starch during retrogradation.