Microwave stabilization and process optimization of rice bran cultivar <i>Jhelum</i>

Abstract

This study was optimizing microwave stabilization process of rice bran obtained from freshly milled paddy (Jhelum variety) using response surface methodology. This study was conducted at different moisture contents (12%–30%), sample weight (5–250 g), and heating time (1–5 min) which were examined to determine their influence on dependent variables––free fatty acids (FFAs) and color coordinates. Regression analysis showed effective influence of microwave heating on all response variables studied. Stabilization treatments resulted in reduction of FFAs, prime indicator of lipase activity, indicating that hydrolytic rancidity could be prevented thereby making it fit for human consumption and food applications. The optimum conditions obtained for microwave stabilization were found to be 16% sample moisture, 100 g sample weight, and 4 min microwave heating time. Proximate analysis showed that crude fat and crude fiber contents reduced while crude protein and ash contents increased after microwave heat treatment in rice bran. Practical applications Rice bran has the ability to be used as a food ingredient and oil source to satisfy the growing oil demands. However, the individual cells are disturbed and the inherent lipase enzyme comes into contact with fat during milling process while extracting bran layer from endosperm. This causes hydrolysis of fats to free fatty acids (FFAs) and glycerol leading to the development of hydrolytic rancidity which is responsible for off-flavor development during storage. The rate of oil degradation and FFA formation can be very high (about 5%–7% per day and 70% in a month) under favorable conditions. Bran oil with an excess of 10% FFA is unfit for human consumption. Now-a-days efforts are being made to stabilize the rice bran using stabilization techniques in order to improve its utilization in food. The microwave stabilization technique seems to be a wiser approach to widen the utilization of rice bran in food industry.