Rice kernel phenolic content and its relationship with antiradical efficiency

Authors: Goffman, Fernando; Bergman, Christine

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2004
Publication Date: 6/10/2004
Citation: Goffman, F.D., Bergman, C.J. 2004. Rice kernel phenolic content and its relationship with antiradical efficiency. Journal of the Science of Food and Agriculture. 84:1235-1240.

Interpretive Summary: Rice bran is a byproduct of the rice milling process that contains phenolic compounds. Rice phenolics exert beneficial effects on human health and may protect food against oxidative deterioration. Information about the concentration of these compounds as well as their antioxidant properties are very limited in rice. We have evaluated under field conditions a large germplasm collection selected for pericarp color diversity and analysed for phenolic content in the kernel. In this study we have confirmed previous results that suggested that phenolic content is strongly related to the pericarp color. Indeed, red and purple cultivars showed a much higher concentration of phenolics than light-colored cultivars, which was on average 10-times higher. The variation found for the studied trait can be used to increase the phenolic content in rice kernel.

Technical Abstract: Plant phenolics exert beneficial effects on human health and may also prevent oxidative deterioration of food. Two field experiments were carried out for characterizing phenolics in rice. The first assay was conducted in 1999 and 2000 in Beaumont, Texas and included five light-brown, two purple and ten red pericarp colored cultivars. `Bran color¿ was highly statistically significant for both bran phenolics concentration and antiradical efficiency (p<0.001). `Year¿ and its interaction with bran color were not significant for the analysed traits, suggesting that seasonal differences and their interactions may not affect phenolics content or antiradical efficiency. The accessions ranged from 3.1 to 45.4 mg gallic acid equivalents (GAE) g-1 bran, and from 10.0 to 345.3 µM trolox equivalents (TE) g-1 bran for total phenolic contents and antiradical efficiency, respectively. The light-brown bran genotypes exhibited the lowest values for phenolic contents and antiradical efficiency whereas red bran ones displayed ca. 10 times higher total phenolic content and more than 50 times higher tannin content than light-brown ones. The two purple lines showed either low or high values for the studied traits. Antiradical efficiency of rice bran extracts was highly positively correlated with total phenolic content (r= 0.99***), suggesting that phenolics are the main compounds responsible for the free radical-scavenging activity in rice bran extracts. In the second field experiment (Stuttgart Arkansas, 2001, and Beaumont Texas, 2000), one hundred thirty three colored rice cultivars were analysed for total phenolic content in whole grain. The accessions showed a large variation for total phenolics, ranging from 0.69 to 2.74 GAE g-1 grain. The data confirmed previous results suggesting bran color as the main factor affecting phenolic concentration in rice kernel and seasonal effects and their interactions as not significant. The results also confirm that within red and purple bran groups it can be found the highest phenolics concentrations in rice kernel.