Genotypic variation in color and discoloration potential of barley-based food products

Barley has a variety of potential food uses. However, the dark gray color of the final products negatively affects consumer acceptability. We determined the discoloration potential of barley from different classes and genotypes, and evaluated the relationship of barley composition, total polyphenol content, and polyphenol oxidase (PPO) activity with discoloration potential of barley. Barley grains were abraded, milled into flour, and analyzed for composition, total polyphenol content, and PPO activity. Total polyphenol content of abraded barley, expressed as gallic acid %, was lowest in hulled proanthocyanidin-free barley (0.02-0.04%), followed by hulled proanthocyanidin-containing barley (0.11-0.18%), and hull-less barley (0.19-0.26%). PPO activity of abraded kernels ranged from 62.1 units/g in hulled proanthocyanidin-containing Baronesse to 116.5 units/g in hulled proanthocyanidin-free CA803803. Dough sheet brightness (L* value) was the best indicator of discoloration potential of barley. Large variation in L* value of dough sheets was observed among different classes and among genotypes within classes. Brightness of dough sheets measured at 24 hr were significantly higher in hulled (65.3-78.1) than in hull-less (59.0-63.9) barley, and within hulled barley, higher in proanthocyanidin-free (72.2-78.1) than in proanthocyanidin-containing (65.3-69.6) barley. Total polyphenol content significantly correlated with the discoloration potential of barley. Protein content and ash content also had a significant negative correlation with discoloration of dough sheets. The results indicated that polyphenol compounds may play a major role in discoloration potential of barley-based products.