Effects of degree of milling on phenolics and antioxidant activity of cooked rice during in vitro digestion

Abstract

Background and objectives The degree of milling (DOM) can affect the phenolics and antioxidant activity of brown rice, but rice as food needs to be cooked and plays its role when passing through the digestive system. Yet, digestion has a significant impact on the phenolic content and antioxidant activity. This study aimed to investigate the effects of DOM on the phenolics and antioxidant activity of cooked rice during in vitro digestion and how these phenolics and antioxidant activities are affected by in vitro digestion. Findings After in vitro digestion, as the DOM increased from 0% to 12.31%, the total phenolic content (TPC), total flavonoid content (TFC), DPPH•, and ABTS•+ scavenging activities decreased by 26.8%, 68.5%, 48.8%, and 29.9%, respectively. The maximum release amount of phenolics occurred at the intestinal digestion phase for all cooked rice samples. The increased proportions of DPPH• and ABTS•+ scavenging activities at every stage were not consistent with those of TPC and TFC. Compared with control samples, the TPC and TFC, DPPH•, and ABTS•+ scavenging activities significantly increased in most digested samples. Conclusions The increased DOM resulted in loss of phenolics including flavonoids and phenolic acids in digestion samples as well as in DPPH• and ABTS•+ scavenging activities of cooked rice. The release of phenolics and the improvement of antioxidant activity of cooked rice during in vitro digestion were mainly due to the digestive enzymes. Significance and novelty Compared with traditional organic solvent extraction combined with alkaline hydrolysis, the in vitro digestion model simulated the digestive process of food in the human body, making the evaluation of rice with different DOMs more practical.