Study On The Stabilization Of Rice Bran By Enzymatic Method And By Microwave Heating

Rice bran is a mixture of pericarp, germ and broken rice. It is rich in nutritionalcomponents of coarse rice. The fresh rice bran is easy to rancid, which can affect itsapplication. The current reported stabilization methods include chemical treatment,heating, extrusion cooking, enzymatic hydrolysis and microwave heating. Microwaveheating is just at research phase, not used in industrial production, but it has its ownadvantages. Microwave heating is rapid, easy to operate and of high efficiency ofelectricity transforming to heat. It is suitable for the small-scale industrial production.It was reported overseas by patents that protease can be used to deactivate lipase andto stabilize rice bran. By far, there are no domestic reports on the topic. In this paper,three commercial proteases were tested to stabilize rice bran. Procedure andeffectiveness of enzymatic stabilization were discussed. Effects of three methods ofmicrowave heating, oven heating and treatment with HCl on stabilization and onantioxidant activity of rice bran were also investigated. Finally, the application of ricebran in steamed bread was studied.In this paper, effects of three commercial proteases（alcalase, papain and neutralprotease）on lipase deactivation of rice bran were studied and evaluated by thedetermination of residual lipase activity. Results showed that neither of threeproteases could reduce lipase activity of rice bran. When tested on commercial lipase,also neither of three proteases could show obvious deactivation effect.The effect of moisture content of rice bran, microwave power and heating time,on stabilization of rice bran was studied. After exposure to microwave, the residualperoxidase activity was determined. It was evident by experiments that the moisturecontent of rice bran was the key element for the stabilization. The residual peroxidaseactivity of rice bran could be reduced to less than1%of original activity afterstabilization under condition of moisture content:24%, heating time:90s, microwavepower:640KW. The acid value of microwave-heated rice bran was18.7%of that offresh rice bran after storage at35℃for6weeks.The aim of rice bran stabilization is not only to deactivate the lipase, but also toreduce the loss of nutritional and bioactive components during the process. Effects ofthree methods of microwave heating, oven heating and treatment with HCl onresidual peroxidase activity, polyphenol content, DPPH radical scavenging rates,reducing power and inhibition of linoleic acid peroxidation were investigated. Resultsshowed that the residual peroxidase activities of rice bran with microwave heating,oven heating and HCl treatment were0.7%,1.6%and7.8%that of fresh branrespectively, and DPPH radical scavenging rates were89.0%、79.4%and63.5%. Rice bran stabilized by microwave heating and oven heating had similar inhibition oflinoleic acid peroxidation and reducing power, both lower than fresh bran and higherthan acidified bran. The antioxidant activity of rice bran extracts could be increasedeffectively by increasing the concentration of extracts.Effects of adding rice bran on quality of steamed bread and the improvedmethods were studied. The experimental results showed that with more addition ofrice bran to flour, steamed bread becomes smaller and poorer in sensory quality.Increasing gluten content of flour properly can prevent the decrease in volume ofsteamed bread. Using sodium bicarbonate solution to decrease fatty acids in rice brancan reduce bad smell of hot steamed bread. Considering both nutrition and flavor ofsteamed bread, steamed bread with the addition of10%~15%of rice bran isadvisable.