The health benefits of eating barley have renewed our interest in its food uses. Dark-gray color appearing in barley foods, however, limits its prevalent use by food processors and consumers. We observed a large variation in the discoloration potential among barley genotypes, as determined by the brightness of flour dough and gel, polyphenol content and polyphenol oxidase (PPO) activity. Genotypic influence was greater than environmental factors on polyphenol content, PPO activity and discoloration potential of barley. Removal of the outer layer of barley grain, heat treatment, exclusion of oxygen and use of ascorbic acid effectively retarded the discoloration in flour dough and gel. Barley grain contained phenolic acids, catechin, and six dimeric and trimeric proanthocyanidins (PAs). Significant increase in discoloration of dough by addition of PAs and considerable reduction in discoloration of dough by heat treatment of flour further indicate that both polyphenols and PPO are responsible for the discoloration of dough. Despite its low concentration, monomeric PA fraction composed mainly of catechin was most capable of causing the discoloration of barley flour dough.
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