Levels of avenanthramides and activity of hydroxycinnamoyl-CoA:: Hydroxyanthranilate N-hydroxycinnamoyl transferase (HHT) in steeped or germinated oat samples

Concentrations of avenanthramides and activity of the biosynthetic enzyme hydroxycinnamoyl-CoA:hydroxyanthranilate N-hydroxycinnamoyl transferase (HHT) were analyzed in dry or, steeped nonmilled or milled, non-heat-treated (raw) or heat-treated oat samples (Avena sativa L.). Increased avenanthramide concentrations were found when intact raw groats were steeped. The increase was time- and temperature-dependent and maximal after 10 hr of steeping at 20degreesC. Continuous germination in air, after steeping, only contributed to a further increase in avenanthrantides when steeping times were shorter than 10 hr. Concentrations of avenanthramides and HHT activity were positively correlated during steeping of intact groats at 8 and 20degreesC. The increase in avenanthramides was suggested to be due to de novo synthesis and a whole grain structure seemed to be required as no increase was found when groats were milled before steeping. Avenanthramide levels also increased when heat-treated samples, lacking HHT activity, were steeped. This increase may be due to release of bound forms, possibly formed during the preceding heat treatment.