Modifications of Tryptophan Oxidation by Phenolic-Rich Plant Materials
2008
Salminen, Hanna | Jaakkola, Helena | Heinonen, Marina
The role of plant phenolics as possible antioxidants was studied toward oxidation of tryptophan. Sources of plant phenolics included byproducts of deoiling processes, such as camelina, rapeseed, and soy meals and Scots pine bark drink, as well as berry phenolics from raspberry, black currant, and rowanberry. The oxidation of tryptophan and its individual oxidation products with and without added phenolics were analyzed by using a validated high-performance liquid chromatography method with diode array and fluorescence detection. Tryptophan in the presence of hexanal and iron (FeCl2) was degraded by 77% after 6 days of oxidation, resulting in oxidation products, such as 3a-hydroxypyrroloindole-2-carboxylic acid B, dioxindolylalanine, 5-hydroxy-tryptophan, kynurenine, N-formylkynurenine, and β-oxindolylalanine. The tryptophan modifications formed upon hexanal and iron treatment were efficiently inhibited by camelina meal followed by rapeseed meal and soy meal. In contrast, phenolics from raspberry, black currant, and rowanberry acted as weak pro-oxidants.
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