Ipek Bayram

Developing antioxidants interventions to retard lipid oxidation reactions
Determining and analyzing antioxidant synergism in different food matrices

Teaching assistant for a general Food Chemistry Laboratory course (40 students)
Designed and prepared eight different undergraduate level food chemistry experiments
Supervised students with using laboratory equipments and learning experimental procedures
Trained and mentored many Masters, PhD, Postdoc, and Visiting students/scholars on basics of lipid oxidation, antioxidants, laboratory equipments and designing experiments

Investigated production lines and processes
Assessed beer quality (iodine value, degree of fermentation, filterability, pH measurement, turbidity, color, carbon dioxide, and foam analysis)
Prepared a detailed report for production process, operating conditions, raw materials, product capacity, quality control tests and mass/energy balances

The kinetics of lipid oxidation includes a lag phase followed by an exponential increase in oxidation products, which cause rancidity. Current models focus on the slope of this exponential curve for shelf-life estimation, which still requires the measurement of full oxidation kinetics. In this paper, we analyzed the formation of lipid oxidation products in stripped soybean oil containing different levels of α-tocopherol. The lag phases of lipid hydroperoxides and headspace hexanal formation were found to have a strong positive correlation with the α-tocopherol depletion time. We propose that the kinetics of antioxidant (α-tocopherol) depletion occur during the lag phase and could serve as an early shelf-life indicator. Our results showed that α-tocopherol degradation can be described by Weibull kinetics over a wide range of initial concentrations. Furthermore, we conducted in silico investigations using Monte Carlo simulations to critically evaluate the feasibility and sensitivity of the shelf-life prediction using early antioxidant degradation kinetics. Our results revealed that the shelf life of soybean oil may be accurately predicted as early as 20% of the overall shelf life. This innovative approach provides a more efficient and faster assessment of shelf life, ultimately reducing waste and enhancing product quality.

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.

α-Tocopherol (α-TOC) and myricetin (MYR) synergistically inhibit lipid oxidation in bulk oil but the mechanism underlying this effect is unknown. In this research, stripped soybean oil (SSO) was treated with α-tocopherol (50μM), myricetin (10–250μM), and their combinations. Taxifolin (TAX) was also tested because it has structural similarities to myricetin but with a higher redox potential. α-Tocopherol: myricetin ratios of 5:1, 2:1, 1:1, 1:2, and 1:5 resulted in extended lag phases ranging from 16 to 99 days, with lag phase increasing with increasing myricetin concentrations. Synergism between α-tocopherol and myricetin was also observed in phospholipid-containing bulk oils both in the absence and presence of reverse micelles, although the reverse micelles shortened the lag phases. Myricetin (redox potential=360 mV) delayed the oxidation of α-tocopherol (redox potential=500 mV) whereas taxifolin (redox potential=500 mV) did not. Both myricetin and taxifolin were able to chelate iron as determined by UV–VIS spectroscopy. These results suggested that the lower redox potential of myricetin allowed it to produce synergistic antioxidant activity potentially by regenerating oxidized α-tocopherol and through its ability to decrease oxidation by metal chelation.