Phenolics characterization and antioxidant activity of six different pigmented Oryza sativa L. cultivars grown in Piedmont (Italy)

•Six different colored Oryza sativa L. cultivars grown in Piedmont were compared.•Black rice showed higher contents of phenolics, flavonoids, and anthocyanins.•Cyanidin-3-glucoside was the major anthocyanin in black rice grains.•Black rice showed higher antioxidant activity compared to white and red ones.

The three principal black rice varieties grown in Piedmont (Artemide, Venere, Nerone) have been studied in comparison with other three at different pigmentations: red (Ermes, Russ) and white, partially refined (Selenio). The extracts from these six different cultivars, processed as “husked” rices, were analyzed by high-performance liquid chromatography coupled with diode array detection and electrospray ionization-mass spectrometry (HPLC-DAD-ESI-MS/MS). Both qualitative and quantitative characterizations of the flavonoids (anthocyanins, flavonols, and flavan-3-ols) and non-flavonoid (hydroxycinnamic acids) phenolic compounds were achieved. 2,2-Diphenyl-1-picrylhydrazyl radical (DPPH) scavenging activity and total phenolic content were evaluated to determine the antioxidant properties of different rices. Black rice showed higher contents of phenolics, flavonoids, and anthocyanins showing higher antioxidant activity when compared to white and partially if compared to red rices. Cyanidin-3-glucoside was the major anthocyanin in black rice grains, followed by peonidin-3-glucoside and cyanidin-3-rutinoside. With respect to the diglycosyl anthocyanins, cyanidin-3-O-gentiobioside was confirmed and quantified in black varieties. Significant differences in phytochemical content and antioxidant activity were achieved also among the three black varieties. The results demonstrate that the black rice varieties contain a rich heterogeneous mixture of phytochemicals which may provide a basis for the potential health benefits, and highlights the rice as a functional food.