Characteristics of Jasmine Rice (Oryza sativa L.) after Milling and Denaturing of Bran Oil Enzyme

Abstract

To produce a premium grade of milled jasmine rice, postharvest techniques employing heat andethanol were evaluated. Milled rice samples were heated using a modified vacuum-microwave oven orexposed to heat-moisture treatment and heat-moisture treatment in combination with different amountsof ethanol vapors. These treatments were done in order to prevent degradation of the residual bran oil onthe surface of the milled rice. After treating and storage for 3 months, the physico-chemical characteristicsrelated to quality of milled rice samples were determined. The results showed that heat-moisture treatmentand heat-moisture treatment in combination with ethanol vapor reduced free fatty acids on the milled ricesurface comparing with microwave and untreated rice. All heat and heat in combination with ethanoltreatments did not affect color of the milled rice as verified by L* a* b* values. Scanning electronmicroscope (SEM) analysis indicated that the surface of milled rice and the starch granule morphologywere not affected by condensation of the ethanol vapor or heat generated during treatments and confirmedby the similar pasting curves in all samples analyzed. In the present study, the effect of direct spraying ofethanol into milled rice during polishing step was investigated. It was found that the ethanol assist-polishedrice had low b* and n-hexanal values comparing with ordinary water assist-polished rice. Both polishingtechniques produced milled rice having the same amount of 2-acetyl-1-pyrroline. Application of ethanoltherefore, shows the potential of this practice in improving color and aroma quality of the jasmine rice.

Keywords : Rice Quality / Free Fatty Acid / Pasting Property / 2-acetyl-1-pyrroline / n-hexanal