Oxidation of emulsified oat proteins

A review of the literature emphasised the significance of protein oxidation, which can lead to such modifications as the loss of essential amino acids and protein cross-links, and may bring about adverse effects on human nutrition and protein functionality. As the globulin fraction constitutes the predominant storage protein in oats, oxidation of oat globulin is in great need of attention and understanding. Oat globulin-containing oil-in-water emulsions were used as a food model. Thus, the objectives of the present work include the oxidation of oat proteins as well as lipid oxidation in prepared food emulsions together with a commercial oat protein-containing cream, and the possible antioxidant activities of berry phenolics (i.e. ellagitannins) towards protein oxidation. Oat globulin was extracted with a cold isolation buffer preceded by the removal of water-soluble impurities. Oxidation took place in darkness by placing the emulsion and cream samples in an oven with continuous stirring and a constant temperature at 37 oC. Sampling for lipid and protein oxidation measurements was carried out at day 0, 3 6 and 9. During the 9-day oxidation, no hexanal was detected in any oat protein-containing samples except for the ones without oat proteins, which were measured by headspace gas chromatography. The development of protein oxidation in prepared emulsions could not be revealed by the proposed loss of tryptophan fluorescence, as the tryptophan fluorescence actually increased and then decreased in the current study as opposed to continuous decrease as indicated in references, but carbonyl and dityrosine formation reflected the progression of protein oxidation. However, the same fluorescence techniques as in prepared emulsions ended up with contradictory fluorescence results in cream samples due to syneresis of oat creams during oxidation. In conclusion, fluorescence spectroscopy is a promising technique to investigate protein oxidation in food emulsions using carbonyl and dityrosine formation as oxidation markers