Metabolite profiling and antioxidant activities of white, red, and black rice (Oryza sativa L.) grains

Abstract

In the present study, several lipids- and water-soluble metabolites from white, red, and black rice were analyzed using HPLC–DAD, GC–FID, and GC–MS/MS. The quantitative data showed that black rice contains the highest amount of cyanidin (4.34 mg/g), γ-oryzanol (380.2 µg/g), total folate (39.1 µg/100 g), tocols (tocopherols and tocotrienols; 21.7 µg/g), all-E-lutein (7.14 µg/g), polyunsaturated fatty acids (37.7%), and total phenolic contents (4.88 mg gallic acid eq./g). Additionally, the ascorbic acid equivalent (AAE) antioxidant assays showed that the metabolites from black rice were potent scavengers of ABTS cations (18.99 mg AAE/g) and DPPH radicals (16.20 mg AAE/g), probably because of the presence of high contents of phenolic (e.g., anthocyanin) and non-phenolic compounds (e.g., carotenoids, tocols, and γ-oryzanols). Among the studied metabolites, the least variation was recorded for fatty acid composition. In the three types of rice grains, oleic acid (C18:1n9c) was found in the highest quantity (38.60–40.35%), followed by linoleic (LA; C18:2n6c) and palmitic acid (C16:0) (18.90–21.15%). Overall, black rice was found to be the most abundant source of nutritionally important compounds, followed by red rice and white rice. Thus, this study provides a basis for the incorporation of pigmented rice into our daily diet for potential health benefits.