Avenanthramide content and related enzyme activities in oats as affected by steeping and germination

Samples from three different oat (Avena sativa L.) cultivars, Vista, Gem and Dane were steeped and germinated in a pilot plant malting system. The content of avenanthramides, antioxidant compounds unique to oats, and some unknown compounds as well as the activities of the avenanthramide-synthesising enzyme hydroxycinnamoyl-CoA:hydroxyanthranilate N-hydroxycinnamoyl transferase (HHT) and the avenanthramide-oxidizing enzyme phenoloxidase (PO) were measured. An increase in avenanthramide content of germinated seeds, as compared to raw grains, was observed for Dane (125%, p < 0.001) and for Vista (29%, p = 0.007). The HHT activity increased 62% (p = 0.014) in Dane, whereas no change was detected in Vista and Gem. The PO activity decreased slightly during the germination process for Gem (p < 0.001) and Vista (p = 0.005). Many of the unknown compounds increased significantly during germination in all three cultivars, and one of them was identified to be the avenanthramide N-(4′-hydroxy-3′-methoxy-(E)-cinnamoyl)-5-hydroxy-4-methoxyanthranilic acid. This study indicates that a highly controlled steeping and germination process can be a valuable method to increase the content of endogenous avenanthramides in oats.