Phytochemical Properties, Antioxidant Activities, And Cytotoxicity Of Ethanolic Bran Extracts From Philippine Pigmented Rice Cultivars

Antioxidants are widely recognized for their immune-enhancing and disease-preventing properties. However, there are some reports that certain synthetic antioxidants can pose carcinogenic effects on human cells. Therefore, it is vital to look for an alternative source of natural, effective, and safe antioxidants for human consumption. In this study, ethanolic extracts of six pigmented rice bran samples were evaluated for their phytochemical properties, antioxidant activities, and cytotoxicity against normal human blood lymphocytes (NHBL). Results showed that the pigmented rice bran extracts had high total phenolic (70.1-178.4 mg.g(-1) gallic acid equivalent), flavonoid (123.3-378.0 mg.g(-1) rutin hydrate equivalent), and anthocyanin (0.8-152.5 m.g(-1) cyanidin-3-glucoside) content. They also had strong antioxidant activities that ranged from 116.4 to 461.7 mg.g(-1) trolox equivalent (TE) for ferric reducing antioxidant power (FRAP) and 85.4-367.7 mg.g(-1) TE for 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radical cation scavenging activity (ABTS-RCSA). All sample extracts showed low levels of effective concentration (EC) at 50 (EC50) (11.6-30.3 mg.L-1) and 25 (EC25) (1.2-10.1 mg.L-1), which is a good indication of high antioxidant activities. Pearson's correlation analysis revealed that there was a moderate to very strong positive correlation (R value: 0.623-0.993) among the phytochemical properties and antioxidant activities tested. Furthermore, pigmented rice bran extracts (100-1000 ppm) showed no toxic effect against NHBL, which implies that all samples are safe for human consumption. Therefore, pigmented rice bran extracts can be used as key ingredient in the development of safe and effective functional food and pharmaceutical products.