Retardation of oxidation by residual phytate in purified cereal beta-glucans

Polysaccharides stabilize emulsions against phase separation and oxidation. This study focused on the role of molecule weight, origin, and residual phytate in the antioxidant activity of β-glucans. The antioxidant activity was investigated by measuring the retardation of lipid oxidation, iron binding capacity and hydroxyl radical scavenging ability of purified oat and barley β-glucans. Low molecular weight β-glucan stabilized the emulsions against phase separation and oxidation better than high molecular weight β-glucan. The oxidative stability of the emulsions, however, correlated to the content of residual phytate in the β-glucan samples. Oat β-glucans which contained higher amount of residual phytate showed higher antioxidant activity than barley β-glucans. When phytate was removed from the β-glucan samples by ion exchange, the antioxidant activity of all β-glucans was reduced to the same level. The study therefore showed that residual phytate played a major role in the antioxidant activity of cereal β-glucans. The study highlights that even at low concentration, phytate content should be considered when evaluating the antioxidant effect of plant polysaccharide extracts.