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Tentative Avenanthramide-Modifying Enzyme in Oats

¹Department of Food Science, Swedish University of Agricultural Sciences (SLU), P.O. Box 7051, SE-750 07 Uppsala, Sweden. ²Institute of Chemistry, Department of Organic Chemistry, Uppsala University, P.O. Box 531, SE-751 21 Uppsala, Sweden. ³Corresponding author. E-mail: Lena.Dimberg@lmv.slu.se. Phone:+46 (0)18 67 10 00. Fax: +46 (0) 18 67 29 95.

A decrease of the concentration of the synthetic avenanthramide N-(4′-hydroxy-(E)-cinnamoyl)-5-hydroxyanthranilic acid in a buffered slurry of milled oat groats (Avena sativa L.) was temperature and pH-dependent, with a maximum rate at 30°C and pH 9. The reaction was inhibited in the presence of 2-mercaptoethanol, acetic acid and at high temperature; suggestive of enzymatically catalyzed nature. Among eight different synthetic avenanthramides tested, the tentative enzyme had highest affinity for avenanthramides comprising caffeic and p-coumaric acids and lowest for those comprising sinapic and ferulic acids. The activity was found in samples from several oat cultivars and was equally pronounced in both bran and endosperm flour of oats. Steeping of oat grains did not influence the reaction.