The Effect of Cooking and Simulated Digestion on the Antioxidants and Minerals in Rice Grains: A Predictor for Nutritional Efficiency

Abstract

Antinutrients in rice tend to impair nutrient bioavailability; hence, this study aimed to investigate the effects of cooking and simulated digestion on the antioxidant activity and phenolic content of white and brown rice, as well as the bioavailability of some minerals. The rice grains were cooked in a pressure cooker, using a 1:2 (w/v) rice-to-water ratio. The digestion of the cooked rice grains was then simulated using pepsin and pancreatin systems. The phenolic (total, free, and bound) and flavonoid content; antioxidant activity (DPPH, ABTS, and FRAP); phytic acid and tannin levels; and mineral HCl-extractability were all determined in the raw, cooked, and digested grains. The cooking process significantly lowered (p ≤ 0.05) the phenolic content of the white rice; however, the phenolic content increased significantly (p ≤ 0.05) when these cooked grains were digested. The phenolic content of brown rice decreased at a higher rate during cooking than that of white rice, and it recovered at a lower rate after digestion. The flavonoid content in both cooked and digested white and brown rice followed a similar trend with the phenolic content. This reduction in the phenolic and flavonoid content in both types of rice after cooking was associated with a large decrease in antioxidant activity, whereas, after digestion, it was associated with a considerable increase. After cooking, the levels of phytate and tannin in both types of rice decreased significantly (p ≤ 0.05), and this drop was even more pronounced in the digested grains. Although the mineral content in the cooked samples of white and brown rice decreased, it recovered after digestion; however, the mineral content remained lower than that of the raw samples. Despite this, there was also a rise in the bioavailability of the minerals in the cooked rice after digestion (p ≤ 0.05), which was considerably higher than the rise in the mineral content itself. The findings indicate that, while cooking rice decreases its phenolic content and antioxidant activity, it also lowers its antinutrient content. Additional benefits were also noted following the simulated digestion.