Phenolic compounds in oats

This research project examined how to treat raw oat material for oat-based food products in order to sustain or increase the levels of phenolic compounds. The focus was mainly on the avenanthramides, which are potentially health beneficial bioactive components found exclusively in oats. A proposed enzymatic decrease in avenanthramide levels when non heat-treated milled oats are steeped in water was investigated. The decrease was strongly suggested to be caused by a polyphenol oxidase. Although the avenanthramides are only found in oats, the polyphenol oxidase enzyme that acted on avenanthramides was also found to be present in wheat, barley and rye. The effects of a highly controlled steeping and germination process on levels of phenolic compounds and related enzyme activities in oats were studied. The process resulted in increased levels of avenanthramides and some unknown compounds to various extents depending on cultivar. This increase was suggested to be partly due to enzymatically catalysed de novo biosynthesis. Whether germination was the reason behind elevated levels of avenanthramides in one harvest year compared with another, in the same oat genotypes, were investigated. The differences in avenanthramide levels between the two years could not be explained by preharvest sprouting of the oat grains in the field. The content and location of tricin was studied in various oat samples. Tricin was found to be localised to oat hulls and was detected and quantified in a minority of all oat samples analysed. The overall conclusion was that germination of oats can be a good method to sustain or increase avenanthramides and other potentially health beneficial phenolic compounds. It is important to inactivate the polyphenol oxidase present in oats and other cereal grain ingredients included in oat-based food products, since it may otherwise decrease the levels of avenanthramides in these products. Oat hulls may be a good source of tricin if high-tricin cultivars are chosen