Sorghum phenols as antioxidants

Abstract

Sorghum varieties grown in Texas in 1998 and 1999 were analyzed for tannins, phenols and anthocyanins. Representative varieties of black, brown, red and white sorghums were decorticated to sequentially remove bran fractions, which were also analyzed for tannins, phenols and anthocyanins. Selected fractions were analyzed for oxygen radical absorbance capacity (ORAC), proximate composition and dietary fiber. Wide variations in phenol levels were observed with values ranging from 0.07-2.45 mg gallic acid equivalents (GAE)/100 mg. Only brown sorghums had significant levels of tannins which ranged between 1.5 and 5.6 mg catechin equivalents (CE)/100 mg. Anthocyanin levels ranged between 24-40 abs/g/ml among the black sorghums, and between 1.5-7.2 abs/g/ml among the red and brown sorghums. Maximum tannin levels in brown sorghum brans ranged between 7.4-17.5 mg CE/100 mg. The brown sorghum brans generally had higher levels of phenols than the other sorghums, with maximum values ranging between 3.0-7.2 mg GAE/100 mg. The black and red sorghum brans attained maximum phenol values of between 1.7-3.2 mg GAE/100. White sorghum bran had maximum phenol content of 0.6 mg GAE/100 mg. Anthocyanin levels were highest among the black sorghum brans, with maximum values of 318-417 abs/g/ml. The red and brown sorghum brans had maximum anthocyanin values ranging between 6.7 and 40.5 abs/g/ml. ORAC values of the brown and black sorghum brans were higher than that of berries; the early sumac (Br-1) bran had the highest ORAC values (410 mg Trolox equivalents (TE)/g). White sorghum and wheat bran had the lowest ORAC values (23 and 31 mg TE/g respectively) due to their low levels of phenols. Positive correlation was observed between the ORAC value and the level of tannins (r = 0.89) and phenols (r = 0.94) in the sorghum brans. Dietary fiber levels in the bran fractions ranged between 36.1-42.9% dry weight basis. Wheat bran had a dietary fiber value of 47.6%. Sorghum brans have high levels of phenolic compounds with high antioxidant potentials and could be exploited as a source of phytonutrients in foods. The high levels of dietary fiber in these fractions could offer additional benefits.