การเปรียบเทียบการทำงานของเอนไซม์ไลเพสจากรำข้าวดิบและรำข้าวที่สกัดน้ำมันออกแล้ว / ปัทมา ฤาชาฤทธิ์ = Comparison of enzymatic reactions of lipases in rice bran and defatted rice bran
The purpose of this research was to study the comparison of enzymatic reactions of lipases in rice bran and defatted rice bran. The chemical composition of the Chainat 1 rice bran was examined. The moisture content was 12.75% wet basis. Carbohydrate, protein, ash, fat and crude fiber contents were 51.86%, 13.73%, 12.15%, 9.51% and 6.96%, dry basis, respectively. The effect of rice bran production on protein was determined. The amounts of soluble proteins in the Chainat 1 rice bran produced by using traditional and conventional milling methods, and the mixed rice bran produced by using conventional milling method were 2.33, 3.48 and 4.21 mg/ml, respectively. The defatted rice bran had 12.61% protein (wet basis) and 3.48 mg/ml soluble protein. Esterification reaction of rice bran lipase was studied and the defatted Chainat 1 rice bran lipase showed the highest specific activity of 2.15 unit/mg protein. The optimum esterification temperature was 40 oC. The properties of rice bran oil were determined. The L*, a*, and b* values of the rice bran oil were 40.87, -0.42, and 17.54, respectively. The viscosity and refractive index values were 68.08 cP and 1.4698. The amount of free fatty, acid value, and iodine value were 2.97 (% as oleic acid), 5.91 mg NaOH/g oil, and 99.80 g/100 g oil, respectively. Gamma oryzanol content in the rice bran oil was 174.67 mg/100g. The SFA : MUFA : PUFA content in rice bran oil was 19.00 : 42.06 : 38.96 (%g/100 g oli). The study of varying amount of rice bran and defatted rice bran in rice bran oil was conducted. The free fatty acid values which were obtained from 10% and 20% defatted rice bran addition, and 10% and 20% rice bran addition in rice bran oil (12-day storage) were 6.34, 8.95, 5.70 and 8.01 (% as oleic acid), respectively. The properties of rice bran oil, which reacted with defatted rice bran lipase for 15 days, were analyzed. The results showed the increases of free fatty acid, acid value, a* and b*, the decreases of reflective index and L* values, while the iodine value and viscosity were constant. In order to obtain the highest free fatty acid value, the optimum condition for applying rice bran lipase in rice bran oil was the using of 20% defatted-rice-bran lipase reacted with pre-unheated rice bran oil at 40oC. This resulted in increase in gamma oryzanol 3.92%, decrease in linolenic and lignoceric fatty acids 87.18% and 25.86%, whereas increase in myristic fatty acid 10.34%.
