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Analysis of antioxidant synergism and its mechanisms in different food systems

Abstract
Lipid oxidation results in off-flavors, toxic aldehydes, and co-oxidation of proteins and color compounds. Combining antioxidants to achieve synergistic interactions has been practiced for decades to improve oxidative stability. Nevertheless, synergism mechanisms have been poorly understood and rarely studied. This dissertation examines the mechanisms of antioxidant synergism in a model system with α-tocopherol (α-TOC) and myricetin (MYR). The interactions between α-tocopherol and taxifolin (TAX) were also tested because it has structural similarities to myricetin but has a higher redox potential. The first part of this research focused on the antioxidant interactions between α-tocopherol and myricetin in stripped soybean oil-in-water emulsions at pH 4.0 and pH 7.0. At pH 7.0, α-tocopherol: myricetin ratios of 2:1 and 1:1 yielded interaction indices of 3.00 and 3.63 for lipid hydroperoxides, and 2.44 and 3.00 for hexanal formation, indicating synergism. Myricetin's ability to regenerate oxidized α-tocopherol and slow its degradation was identified as the synergism mechanism. At pH 4.0, an antagonistic interaction was observed, which was associated with high ferric-reducing activity of myricetin in acidic environment. α-Tocopherol and taxifolin exhibited non-synergistic effects both in acidic and neutral emulsions. This was due to taxifolin's inability to recycle α-tocopherol at both pHs, unlike myricetin, and taxifolin's high ferric-reducing activity at pH 4.0, similar to myricetin. The second part of this research focused on antioxidant interactions between α-tocopherol and myricetin in stripped soybean oil. α-Tocopherol and myricetin ratios of 5:1, 2:1, 1:1, 1:2, and 1:5 resulted in interaction indexes of 1.14, 1.50, 1.55, 1.30, and 1.16, showing synergistic activity for both lipid hydroperoxide and hexanal formation. Synergism was also observed in phospholipid-containing bulk oils, both in the absence and presence of reverse micelles. α-Tocopherol and taxifolin, however, had additive effect at all antioxidant ratios. Antioxidant degradation results showed that myricetin delayed α-tocopherol oxidation, whereas taxifolin did not. These results revealed that myricetin's lower redox potential allowed it to cause synergism through regenerating oxidized α-tocopherol rather than by decreasing oxidation by metal chelation since both myricetin and taxifolin chelated iron. Thus, this study advises combining α-tocopherol with myricetin in bulk oils and neutral oil-in-water emulsions to improve oxidative stability and reduce food waste.
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