Lipid oxidation is a serious concern for the food industry, due to the production of off-flavors and odors, discoloration, and toxic compounds. Oxidation can also decrease the nutritional content in food products. There are two forms of oxygen which participant in lipid oxidation; singlet and triplet. Singlet oxygen (1O2) is a nonradical, high energy molecule that can react directly with fatty acids. Singlet oxygen can be formed during photosensitized oxidation, a process in which a photosensitizer, such as chlorophyll, absorbs light energy and becomes excited. Triplet oxygen (3O2)is the most stable and common form of oxygen. Autooxidation is triplet oxygen mediated lipid oxidation, and requires both the oxygen and the fatty acids to be in radical form.
The lipid oxidation process can be slowed or prevented by compounds known as antioxidants. Tocopherols (α, β, γ, and δ), which are commonly known as vitamin E, have been showed to have antioxidant activity. The present study examines the effect of tocopherol isomers on chlorophyll photosensitized oxidation and heat induced autooxidation of lard. The effects of tocopherol isomers on lard oxidation were measured by headspace oxygen and peroxide value analyses. α-, β-, γ-, and δ-Tocopherol were all found to prevent photosensitized oxidation of lard by quenching singlet oxygen. α-Tocopherol had the highest singlet oxygen quenching rate at 1.42 x 107M-1s-1 followed by β-tocopherol (1.11 x 107M-1s-1), γ-tocopherol (9.70 x 106M-1s-1), and δ-tocopherol (4.23 x 106M-1s-1). Lard thermal stability was increased, via autooxidation inhibition, by γ- and δ-tocopherol. The optimum concentrations were determined to be 250-1000ppm and 500ppm for the γ- and δ-isomer, respectively. α-Tocopherol did significantly increase lard stability, but it was found to have significant prooxidant activity (p<0.05) at concentrations greater than 250ppm.
Tocopherol isomers are able to inhibit both photooxidation and autooxidation in lard, however there is not one isomer that is superior than the others at preventing both types of oxidation.