Characterization of color, phenolic profile, and antioxidant activity of Italian pigmented rice varieties after different technological treatments

Pigmented varieties are rich in different bioactive compounds, including anthocyanins, proanthocyanidins, carotenoids, and phenolic acid, with known antioxidant and anti-inflammatory activity [1,2,3]. Therefore, their consumption could exert beneficial effects on the health of the general population and in particular on that of people suffering from some chronic diseases such as celiac disease. Different pigmented rice varieties are present on Italian market; they are commercialized as brown rice or as a product after a technological treatment (e.g., parboiled, milling). Pigmented rice is commonly consumed as brown rice, but technological treatments could bring some advantages for both producers and consumers (higher milling yield, shorter cooking time, and longer shelf-life) [4] and have positive effects on rice nutritional values in terms of starch availability, glycemic index and/or vitamins and mineral contents. The objective of this study was the characterization of the samples in term of phenolic content and antioxidant capacity tested in vitro. In parallel the impact of two technological treatments (e.g., milling and parboiling) on their phytochemical composition was evaluated. Four pigmented (purple, black, orange, red) and one non-pigmented samples of Italian rice varieties, as such brown or processed with different technological treatments (parboiled and milled) were included in the study. Different spectrophotometric and chromatographic in vitro methods were applied: 1) Folin–Ciocalteu assay, 2) DPPH assay, 3) pH differential method, 4) High-Performance Thin Layer Chromatography (HPTLC), 5) HPLC-DAD method. According to our results, pigmented varieties represent a source of soluble polyphenols and anthocyanins with high antioxidant activity when compared to the non-pigmented ones. However, both technological processes affected the concentration of phenolic compounds and the relative antioxidant property. Milling reduced specifically the content of phenolic compounds and the antioxidant activity, while parboiling affected mainly the presence of anthocyanins. This work was supported by Fondazione Celiachia Onlus (FC) Grant n◦004_FC_2019.