Quantification of polyphenol content, antioxidant properties and LC-MS/MS analysis in Malaysian indigenous rice cultivars (Oryza sativa L.)

Abstract

The study was carried out to evaluate the differences in the total phenolic content (TPC), total flavonoid content (TFC), antioxidant activities via 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulphonic) and 2,2-diphenyl-1-picrylhydrazyl assays and quantification of targeted polyphenol compounds in Malaysian upland and wetland rice (Oryza sativa L. indica) varieties. Of note, the Bario cultivar of upland rice-seed grain extracts had the highest TPC (47.84 mg gallic acid equivalents/g), TFC (7.14 mg rutin equivalents/g) and antioxidant activities 25% higher than for the other cultivars. Ferulic acid, salicylic acid and p-coumaric acid, (the most abundant polyphenol compounds and known as a group of flavonoids responsible for high antioxidant properties) were detected in all extracts tested; upland rice of the Bario cultivar had a higher portion of ferulic acid (10.31 mg/100g), salicylic acid (3.25 mg/100g) and p-coumaric acid (1.10 mg/100g). This finding of antioxidant compounds was further confirmed using liquid chromatography combined with tandem mass spectrometry analysis in which ferulic acid produced the most substantial peak at [M-H]^- m/z 193 to form the daughter ion of 134 at a retention time of 5.79 min, while p-coumaric acid was detected at m/z 163 to form the daughter ion of m/z 119 at a retention time of 4.95 min. The results indicated that the increased antioxidant quantity in upland rice could support the available upland rice grain database for the development of enriched health-promoting foods.