ARS | Publication request: Analysis of Genotypic Diversity in Esterase Activity of Rice Bran

Submitted to: United States Japan Natural Resources Protein Panel
Publication Type: Proceedings/Symposium
Publication Acceptance Date: August 1, 2008
Publication Date: September 30, 2008
Citation: Chen, M., Yan, W. 2008. Analysis of Genotypic Diversity in Esterase Activity of Rice Bran. United States Japan Natural Resources Protein Panel. p. 83-84.

Technical Abstract: Rice bran is a by-product of the rice milling process. It is rich in protein, fat, crude fiber, minerals and vitamins, and is a valuable source of antioxidants. It can be used for ingredients, be developed into a functional food, and can be extracted for rice bran oil production. However, rice bran becomes rancid rapidly after milling due, in part, to the lipase enzyme, which comes into contact with the lipid and hydrolyzes triglycerols into free fatty acids. Stabilizing the bran by inactivating the lipase through a heating treatment can prevent lipid deterioration, but might reduce the levels of heat-labile antioxidants. The objectives of this study are: 1) to analyze the genotypic diversity of esterase activity among 106 genotypes, a subset of rice germplasm from the National Small Grain Collection (NSGC); and 2) to understand the contribution of esterase activity to the hydrolytic rancidity of rice bran during storage. Esterase activity ranged from 0.91 to 5.34 µmol per hour per gram bran with an average of 2.46. When comparing two common US cultivars (2.92 and 3.77) with the germplasm evaluated in this study, it becomes evident that rice varieties with lower esterase activity exist. The linear regression model: 48h hydrolytic rancidity = -7.51 + 8.19 x (esterase activity), explained much of the 48h hydrolytic rancidity to esterase activity (R square= 0.76). Based on this determined relationship, a 3-fold reduction of esterase activity has the potential to reduce ffa accumulation in a 48h period by 5-fold. This indicates that the opportunity exists for improving the hydrolytic stability of bran fraction by reducing the esterase activity of rice through the use of breeding techniques.