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Lipid Oxidation and Quality

Edible Applications Technology

Award Winner

Session:: Oxidation in Emulsions and Structured Systems

Analysis of antioxidant synergism and its mechanisms between alpha-tocopherol and myricetin in stripped soybean oil-in-water emulsions at different pH values

Monday, May 1, 2023
2:50 PM – 3:10 PM MDT
Room: 205
Abstract: Lipid oxidation is a major challenge in food industry since it reduces shelf-life by producing off-flavors. Antioxidant combinations are often effective due to: 1) combination of different protection pathways, such as radical scavenging and metal chelating activities, and/or 2) antioxidants' ability to regenerate each other. This research examined interaction of myricetin with alpha-tocopherol in oil-in-water emulsions. Soybean oil was stripped to remove endogenous antioxidants. Alpha-tocopherol (30 µM), myricetin (6, 15, 30, 60, 150 µM), and their combinations were added to 1% emulsions (pH 4-7) stabilized by Tween20. Lipid hydroperoxides, hexanal formation, and alpha-tocopherol/myricetin depletion were measured for oxidative stability. Interaction index (experimental/theoretical lag phase) was calculated to determine synergism. When alpha-tocopherol:myricetin ratio was 5:1, 2:1, 1:1, 1:2, and 1:5 at pH 7, the indices were 1.67, 2.44, 3.00, 3.20, and 4.79, indicating synergism (index >1). However, when alpha-tocopherol:myricetin ratio was 2:1 and 1:1 at pH 4, the indices were 0.64 and 0.59, showing antagonism (index < 1). By mixing alpha-tocopherylquinone with myricetin and measuring alpha-tocopherol formation by HPLC, it was demonstrated that myricetin (E=360mV) can regenerate alpha-tocopherol (E=500mV) in acidic and neutral emulsions. The fact that myricetin was consumed faster than alpha-tocopherol in both emulsions also suggested alpha-tocopherol regeneration. However, because myricetin has iron reducing and chelating properties, regeneration may not be the sole mechanism. Myricetin's increased ferric reducing activity and inability to chelate ferrous ions at pH4 (by ferrozine assay) were speculated to cause antagonism, as myricetin would increase iron-promoted hydroperoxide degradation. In contrast, myricetin at pH 7 has lower ferric reducing activity and effectively chelates ferrous ions (stronger than EDTA), decreasing its ability to promote iron-induced oxidation and allowing regeneration of alpha-tocopherol to be more effective. This research is significant for food industry since it presents novel strategy to protect emulsion-based foods and provides mechanistic approaches to predict synergism.