Effect of microwave heating or simple heat (pan roasted) treatment of rice bran on the rate of release of free fatty acids during storage at room temperature

Development of Free Fatty Acids (FFA) is a major problem which affects the use of rice bran as a feed ingredient. The purpose of this research was to evaluate the effect of microwave heating and pan roasting on FFA development of rice bran during storage, proximate composition and to study the available phosphorous (P) content. Rice bran from raw and parboiled rice obtained from paddy variety BG 358 was treated using microwave heat and pan roasting. An experiment was conducted in a two-factor factorial with 2×3 factorial design. Treated samples were studied for FFA content up to 8 weeks in weekly intervals. Proximate composition was studied immediately after heat treatment and at the eighth week. Availability of P in rice bran was studied after heat treatment. Both the treatments significantly reduced the formation of FFA in rice bran during storage (P<0.05), while microwave heat treatment showed a higher effect on reduction of the formation of FFA content in raw microwave heated rice bran from 2.68 to 12.44 g 100 g ˗1 and in parboiled microwave heated rice bran from 1.8 to 9.54 g 100 g ˗1 during eight weeks of storage. There was no significant (P>0.05) difference in proximate composition of rice bran during the period of storage in any of the treatments. Both treatments improved P availability; however, pan-roasting had a high effect on P availability where raw pan roasted rice bran and parboiled pan roasted rice bran showed an increment of 17.67 and 19.43%, respectively. It is concluded that pan roast and microwave heat retard development of rancidity in rice bran, although at different degrees. These findings could be used with suitable modifications to the milling and storage processes to improve the quality of the rice bran available for animal feeding in Sri Lanka.