In-vitro Antioxidant Activity and Physiochemical Properties of Some Improved Sri Lankan Red and White Rice (Oryza sativa L.) Varieties

Rice is a staple food providing essential nutrients to populations worldwide. In Sri Lanka, improved red and white varieties of Oryza sativa are widely consumed, yet limited research exists on their nutritional composition and antioxidant properties.  This study aimed to evaluate the antioxidant activity and nutritional properties of selected red and white rice varieties in Sri Lanka.  Six improved rice varieties (Ld408, Ld371, Ld368, Ld376, Ld253, and Ld365) were collected from the Rice Research Institute, Labuduwa, Sri Lanka. Methanolic extracts of the rice grains were analyzed for in-vitro antioxidant activity using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay, the ferric-reducing power activity assay, and the total phenolic content (TPC) assay. Nutritional composition, including total carbohydrate, protein, and amylose contents, was determined using the phenol-sulfuric acid method, Lowry method, and iodine colorimetric method, respectively. Statistical analyses were performed using GraphPad Prism 9, with statistical significance set at p<0.05. The red rice variety Ld408 exhibited the highest antioxidant activity, as indicated by ferric-reducing power, DPPH scavenging activity, and total phenolic content (p<0.05). Among the white rice varieties, Ld368 had the highest carbohydrate content (p<0.05), while Ld408, a red variety, had the highest protein content (p<0.05). The red rice variety Ld376 contained the highest amylose content. The results indicate that while white rice varieties often have a higher carbohydrate content, red rice variants, especially Ld408, possess higher protein content and stronger antioxidant potential. These findings highlight the nutritional benefits of red rice and the necessity of incorporating different types of rice varieties into daily diets to promote dietary diversity.