67B-5 |
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R. J. ELIAS, E. A. Decker, and D. J. McClements. Dept. of Food Science, Univ. of Massachusetts, Amherst, Chenoweth Laboratory, Amherst, MA 01003-1410 Amino acids, such as methionine, cysteine and tryptophan, are capable of scavenging free radicals. It is thought that methionine serves as an important endogenous antioxidant defense mechanism through the scavenging of free radical species within proteins. Both cysteine and tryptophan have also been reported to have high oxidative susceptibility. Therefore, the addition of proteins enriched in methionine, cysteine and tryptophan residues to oil-in-water emulsions could inhibit lipid oxidation. The objective of this study is to assess the antioxidant capacity and oxidation kinetics of methionine, cysteine and tryptophan in b-lactoglobulin (bLG) and bovine serum albumin (BSA) within oil-in-water emulsions. Brij 35-stabilized oil-in-water emulsions (pH 7) containing 25 wt % menhaden oil were homogenized with a probe-style ultrasonicator. The continuous phase surfactant was removed by centrifugation and the emulsions were reconstituted with buffer. Protein (bLG or BSA, 1 wt %) was added to the aqueous phase of emulsions subsequent to dilution (5% final oil concentration). The emulsions were transferred (6 ml aliquots) to glass tubes and stored at 37°C in the absence of light. Samples were tested daily for methionine, cysteine, tryptophan oxidation, as well as for lipid oxidation. Lipid oxidation was inhibited in samples containing bLG or BSA dissolved within the aqueous phase. Amino acid oxidation was observed after 1 day and preceded lipid oxidation, which was observed after 3 days. It can be concluded that methionine, cysteine and tryptophan residues are oxidized before the lipid component of the emulsions, and thus inhibit lipid oxidation by acting as endogenous free radical scavengers. The results indicate that methionine, cysteine and tryptophan in proteins are effective antioxidants in oil-in-water food emulsions and oxidize preferentially relative to lipids. Therefore, the incorporation of proteins, enriched in these amino acids, in oil-in-water emulsions can more effectively inhibit lipid oxidation.
Session 67B, Food Chemistry: Antioxidants and bioactive agents
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