A study of biodiversity of flavonoid content in the rice caryopsis evidencing simultaneous accumulation of anthocyanins and proanthocyanidins in a black-grained genotype

Rice genotypes with pigmented caryopses have received increased attention because of their antioxidant properties. Previous works evidenced that the kernel of red rice is characterized by the presence of proanthocyanidins, whereas black rice is characterized by the presence of anthocyanins. In the present study, the total antioxidant capacity (TAC) and the polyphenol content of the caryopsis were evaluated on a set of Italian rice varieties (three white, two black and five red ones). The pigmented rices, on average, had a TAC four times higher than the white ones. As expected, red-grained genotypes contained no detectable anthocyanins and one black rice contained no detectable proanthocyanidins. However, the black-grained cv. Artemide had large amounts of both proanthocyanidins and anthocyanins. This genotype was also characterized by the highest TAC and polyphenol content: its TAC was about twice the TAC of the other pigmented rices, and it had a polyphenol content 2–3 times the content found in the other pigmented rices. Pigmented genotypes are confirmed to be very interesting to breed rice for high polyphenol content and TAC. Furthermore, the possibility to select for genotypes accumulating both anthocyanins and proanthocyanidins provides a way to substantially increase the polyphenol content and TAC of the rice caryopsis.