RELATIONSHIP BETWEEN HYDROLYTIC RANCIDITY, OIL CONCENTRATION AND ESTERASE ACTIVITY IN RICE BRAN

Authors: Goffman, Fernando; Bergman, Christine

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2003
Publication Date: 1/1/2004
Citation: Goffman, F.D., Bergman, C.J. 2004. Relationship between hydrolytic rancidity, oil concentration and esterase activity in rice bran. Journal of the Science of Food and Agriculture. 80(6):689-392.

Interpretive Summary: The release of fatty acids by enzymatic hydrolisis of lipids limits rice bran utilization in human nutrition. We have studied the intensity of hydrolytic decomposition in rice bran in three groups of cultivars showing different levels of bran oil content (high-, medium- and low-oil concentration) and measured their enzymatic -esterase- activity. The hydrolytic decomposition of bran lipids was strongly related to the esterase activity. No relationship was found between oil content and hydrolytic rancidity. The results suggest that it is possible to create new cultivars with increased stability against hydrolytic rancidity by selecting plants with low esterase activity.

Technical Abstract: Hydrolytic rancidity restricts the utilization of rice bran, reducing its potential value. In the present study, three groups of eight rice cultivars each displaying different levels of oil concentration (high-, medium- and low-oil) were cultivated under field conditions and evaluated for bran oil content, hydrolytic rancidity and esterase activity. Genotype effects were statistically significant for all measured traits (p is less than 0.05), whereas environment (year) was nonsignificant. Hydrolytic rancidity was strongly correlated with esterase activity (r equals 0.89***), but not with oil concentration (r equals -0.01). A wide variation was found for both hydrolytic rancidity and esterase activity, which ranged from 6.8 to 56.0 mg C8:0/g bran (CV equals 49.1 percent) and from 4.3 to 22.8 mg C8:0/g bran (CV= 34.3 percent), respectively. Red bran displayed the lowest values for both hydrolytic rancidity (mean equals 10.2 mg C8:0/g bran) and esterase activity (mean equals 5.4 mg C8:0/g bran). Apparently, the low values for hydrolytic rancidity were related to the inhibitory effect of bran tannins on lipase activity. In conclusion, cultivar variation was detected for both hydrolytic rancidity and esterase activity in the studied genotypes, esterase activity being the principal factor explaining the variation found for the former trait. Therefore it may be possible to create new cultivars with increased stability against hydrolytic rancidity by selecting for lower esterase activity.