HPLC Analysis of Oxidative and Polymerized Decomposition Products in Commercial Vegetable Oils and Heated Fats

A high performance liquid chromatographic (HPLC) method has been developed to analyze oxidative and polymerized decomposition products in commercial vegetable oils and heated fats. The oil was passed through a SEP-PAK where the minor constituents were concentrated. The SEP-PAK was eluted with hexane-ether 1:1 (v/v), and 2-propanol. The first eluate contained unsaponifiables and neutral lipids, and the second eluate contained the more polar oxidative and polymerized decomposition products. The second eluate was analyzed by normal phase HPLC. Five commercial vegetable oils were analyzed, and similarities and differences were observed. Four soybean oil samples from different manufacturers also showed differences. Soybean oil heated at 185°C was collected periodically and analyzed. As the heating time increased, the oxidation and polymerization products also increased. Used frying fat samples from a commercial fried chicken manufacturer were analyzed. The frying oil quality reached an equilibrium during three days of operation, because the oil lost in frying was replenished daily with fresh shortening.