Submitted to: Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2016
Publication Date: 4/6/2016
Citation: Chen, M., McClung, A.M., Bergman, C.J. 2016. Concentrations of oligomers and polymers of proanthocyanidins in red and purple rice bran and their relationships to total phenolics, flavonoids, antioxidant capacity and whole grain color. Food Chemistry 208:279-287.
Interpretive Summary: Proanthocyanidins, also known as tannins, are proposed to have chronic disease modulation properties. Fruits, such as cranberries, apples and grapes, and chocolates are known to contain proanthocyanidins. With the eventual goal of enhancing rice phytonutrient concentrations, we investigated the genotypic variation of the concentrations of proanthocyanidins in dark-pigmented rice brans, such as purple and red color bran of whole grain rice. A 4.3-fold variation in total proanthocyanidins in bran of dark-pigmented whole grain rice was found. Using a non-destructive colorimeter to measure the red color of the whole grain rice, we found that the color of the whole grain rice negatively correlated with the concentrations of the proanthocyanidins suggesting the colorimeter would be an efficient and fast screening tool to select rice containing high proanthocynidins. In conclusion, we identified rice varieties with high levels of proanthocyanidins that can be used for breeding to enhance phytonutrient concentration in rice.
Technical Abstract: Proanthocyanidins, a flavonoids subgroup, are proposed to have chronic disease modulation properties. With the eventual goal of enhancing rice phytonutrient concentrations, we investigated the genotypic variation of the concentrations of individual oligomers and polymers of proanthocyanidins in dark-pigmented rice brans. A 4.3-fold variation in total proanthocyanidins (sum of oligomers and polymers) in the extractable fraction was found and the concentration was highly correlated with total phenolics, total flavonoids and antiradical capacity. Variation in the proportion of oligomers and polymers existed, with monomers to trimers, 4-6mers, 7-10mers and polymers accounting for 7, 18, 26.5 and 48.7%, respectively, of the total. The redness value a* of whole grain rice measured in CIE L*a*b* color space was negatively and positively correlated with extractable and non-extractable proanthocyanidins, respectively. The variation found indicates it is possible to select rice with bran containing high levels of total proanthocyanidins and specific degree of polymerization profiles.