EFFECTS, QUENCHING MECHANISMS, AND KINETICS OF NICKEL CHELATES IN SINGLET OXYGEN OXIDATION OF SOYBEAN OIL

Effects of 0, 7 x 10(-8), 14 x 10(-8), and 21 x 10(-8) M bis(di-n-butyldithiocarbamato)nickel chelate (BTC) and 0, 9 x 10(-7), 18 x 10(-7), and 27 x 10(-7) M [2,2'-thiobis(4-1,1,3,3-tetramethylbutyl)phenolato)](n-butylamine)nickel chelate (TPB) on the singlet oxygen oxidation of soybean oil containing 4.4 x 10(-9) M chlorophyll were determined by measuring peroxide value and depleted headspace oxygen of oil. The samples were stored in the 4000-lx light storage box for 24 h at 20-degrees-C and evaluated for the oxidative stabilities every 4 h in duplicate. The reaction rate constant of singlet oxygen with soybean oil was 1.38 x 10(5) M-1 s-1. As the concentrations of BTC and TPB increased, peroxide values and depleted headspace oxygen decreased significantly at P < 0.05. BTC was significantly more effective than TPB in reducing the singlet oxygen oxidation of soybean oil at P < 0.05. Quenching mechanisms and kinetics of 0, 0.75 x 10(-5), 1.50 x 10(-5), and 3.0 x 10(-5) M BTC and 0, 1.25 x 10(-4), 2.50 x 10(-4), and 5.0 x 10(-4) M TPB in the singlet oxygen oxidation of soybean oil containing 3.3 x 10(-9) M chlorophyll were studied by measuring the depleted headspace oxygen of sample bottles. BTC and TPB quenched singlet oxygen to minimize the chlorophyll photosnsitized oxidation of soybean oil. The total singlet oxygen quenching rate constants of BTC and TPB were 1.23 x 10(9) and 3.70 x 10(7) M-1 s-1, respectively.