Anthocyanin and proanthocyanidin contents, antioxidant activity, and in situ degradability of black and red rice grains.

Objective: An experiment was conducted to assess the antioxidant contents and activities of colored rice grains and to evaluate their nutritive characteristics in terms of chemical composition and in situ ruminal degradation.

Methods: Ten cultivars of colored rice grains (Oryza sativa L.) collected from several areas of Japan were studied, and control rice without pigment, maize, barley, and wheat grains were used as control grains. Their chemical compositions, pigment, polyphenol contents, total antioxidant capacity (TAC), and degradation characteristics were determined.

Results: The starch contents of the colored rice grains were in the range of 73.5% to 79.6%, similar to that of the control rice grain. The black and red rice grains contained anthocyanin (maximum: 5,045.6 μg/g) and proanthocyanidin (maximum: 3,060.6 μg/g) at high concentrations as their principal pigments, respectively. There were significantly (p<0.05) positive relationships among the pigment contents, polyphenol content, and TAC values in the colored and control rice grains, indicating that the increase in pigment contents also contributed to the increased polyphenol content and TAC values in the colored rice grains. The dry matter and starch degradation characteristics, as represented by c (fractional degradation rate of slowly degradable fraction) and by the effective degradability, of the colored rice grains and the control rice grain were ranked as follows among commonly used grains: wheat>barley ≥rice>maize. The colored rice grains also included the most-digestible starch, since their potential degradable fraction and actual degradability at 48 h incubation were almost 100%.

Conclusion: Colored rice grains have high potential to be used as antioxidant sources in addition to starch sources in ruminants.