Cereal Chem. 91(6):560-565Rice bran lipid is rapidly made rancid by endogenous lipase enzymes. To inactivate rice bran lipase, an enzymatic hydrolytic method was developed and then compared with the thermal method. The efficiency of five proteolytic enzymes including trypsin, chymotrypsin, papain, bromelain, and Flavourzyme enzyme to stabilize rice bran was investigated. Moreover, the antioxidant content and storage stability of enzymatically stabilized rice bran (ESRB), thermally stabilized rice bran (TSRB), and raw rice bran (RRB) were studied. Trypsin, chymotrypsin, and papain showed a higher rate of hydrolysis than bromelain and Flavourzyme enzyme. After 120 min of hydrolysis, rice bran hydrolyzed by trypsin, chymotrypsin, and papain inactivated 80, 86, and 79% of lipase activity, respectively, whereas lipase activity of rice bran hydrolyzed by bromelain and Flavourzyme enzyme was higher than the initial rice bran. With a similar lipase inactivation level, the cheaper papain was used to produce ESRB. Total phenolics content of ESRB was 52.89 and 94.10% higher than in RRB and TSRB, respectively. In addition, γ-oryzanol content in ESRB was 2.23-and 2.05-fold of that in RRB and TSRB, respectively. Lipase activity of RRB increased throughout the two months of storage, whereas no change in lipase activity was observed in ESRB and TSRB. At the end of storage, free fatty acid contents of RRB, TSRB, and ESRB were 15.30, 4.67, and 3.92%, respectively. We propose enzymatic hydrolysis by papain for stabilization of rice bran with high antioxidant content and storage stability.

In recent years, there has been increased interest in antioxidants present in food and food products. Intake of foods rich in antioxidants may help to maintain oxido/redox balance and, therefore, normal physiological functioning in a living system (Kaur & Kapoor, 2000). Studies have shown that dietary intake of foods rich in natural antioxidants is correlated with a reduction in the risk of coronary heart disease, cancer, and inflammatory and aging-related disorders (Aune et al., 2018). In the food industry, antioxidants are used to protect food from oxidative deterioration, including rancidity and discoloration. The demand for natural antioxidants has expanded widely. Therefore, new sources of natural antioxidants are desirable for customers and many food industries.Rice is the staple food of people in Asia and many other countries (Zaky et al., 2020). In general, the outer layers of the rice grain, called rice bran, are polished out, due to a consumer's favor for white rice consumption. Unfortunately, most of the rice antioxidants are present in the bran. A large amount of bran as by-products are produced during a milling process and become a big challenge to use valuable rice bran more in