From paddy to polished rice: investigating antioxidant activity and phenolic compounds in Italian conventional and pigmented rice varieties and their by-products

Rice is typically consumed in the polished form, but most of the bioactive compounds are lost by removing the outer layers of the caryopsis. This study proposed to analyze the phenolic pattern, including soluble (SPAs) and bound phenolic acids (CWBPAs) and anthocyanins, and the antioxidant activity of paddy, polished, and unpolished rice, and of outer layers (husk and bran) in fourteen Italian rice varieties. Unpolished black varieties showed higher levels of SPAs and anthocyanins compared to red and brown pericarp varieties. Among byproducts, rice husks were rich in SPAs (497-796 mg/kg) and CWBPAs (4060-7446 mg/kg), making them a cost-effective source of natural antioxidants. Conversely, anthocyanins are characteristic of pigmented bran fraction (2138-5041 mg/kg), which also demonstrates high free-radical scavenging activity and significant ferric reducing ability. These findings are relevant for future application of rice husk and bran antioxidants in functional ingredients and promote the consumption of unpolished pigmented rice varieties.