Variability in resistant starch, vitamins, carotenoids, phytochemicals and in-vitro antioxidant properties among diverse pigmented grains

Abstract

Maize, sorghum, quinoa and rice are important grains which serve as the major source of carbohydrates and micronutrients in the diet. Apart from their normal color, these crops are also cultivated in different colors among diverse regions of the world. In the present study, various pigmented grains including maize, sorghum, rice and quinoa of different color were evaluated for their nutrients, anti-nutrients, phytochemicals and antioxidant activity. Resistant starch, amylose, total starch, and damaged starch contents varied significantly (p < 0.05) among the evaluated samples. Water soluble vitamins, tocols and carotenoids showed wide variability among the grains. The findings showed riboflavin, niacin, pantothenic acid and total folic acid content were found significantly (p < 0.05) higher in red sorghum (177.01 μg/100 g), orange maize (2233.98 μg/100 g), red quinoa (1361.16 μg/100 g) and black quinoa (147.33 μg/100 g), respectively. Total tocopherols and tocotrienols ranged from 35.33 to 192.72 and 17.03 to 231.39 μg/100 g, respectively. Total phenolic, flavonoid and anthocyanin content varied significantly (p < 0.05) and were recorded between 282.12 to 900.54 mg gallic acid equivalents (GAE)/100 g, 120.29 to 174.11 mg catechin equivalents (CE)/100 g and 13.44 to 197.04 mg cyanidin-3-glucoside equivalents (CGE)/100 g, respectively. The total proanthocyanidin content varied significantly among pigmented grains and ranged from 2.11 to 32.18 mg catechin equivalent (CE)/100 g. The free radical scavenging activity evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) varied significantly among samples and was observed between 13.52 to 56.89% and 32.01 to 65.10%, respectively. Reducing power and metal chelating activity varied significantly among pigmented grains and were observed between 3.04 to 5.98 mol ascorbic acids equivalents (Mol AAE)/100 g and 56 to 67.1%, respectively. Maroon maize had the highest phytic acid content of 609.21 mg/100 g. The bioaccessibility of iron (Fe) and zinc (Zn) was found to be higher for both black and red quinoa. Overall, red and black quinoa had low content of phytic acid and high content of nutrient than other pigmented grains evaluated.