Epoxy fatty acids in used frying fats and oils, edible oils and chocolate and their formation in oils during heating

摘要

The occurrence of monoepoxy fatty acids in used frying oils and in other common foods has been determined. Monoepoxy fatty acids with trans-9,10- and cis-9,10-epoxystearate and trans-12,13-, trans-9,10-, cis-12,13- and cis-9,10-epoxyoctadecenoate were found at average levels of 3.7 g/kg in used frying fats and oils, but also at about 2 g/kg in the fat fraction of chocolate. They were also detected in pumpkin seed, sweet almond, groundnut, sunflower, and olive oils at average levels of 3.4, 1.7, 1.4, 1.0, and 0.2 g/kg, respectively. Their formation during heating at 175 degrees C was observed for sunflower, rapeseed, soybean, and linseed oil and compared with the increase of polar compounds and polymerized triacylglycerols as other important quality indicators for frying oils. During heating for 16 h, the level of monoepoxy fatty acids increased to about 30, 18, 8, and 4 g/kg for olive, sunflower, linseed, and rapeseed oils, respectively. The influence of the heating temperature was surveyed for refined soybean oil at 160, 170, 180, and 200 degrees C. Heating of two sets of five different refined and virgin rapeseed oils revealed a significant lower formation of monoepoxy fatty acids for refined oils at a median level of 4.6 g/kg compared to 7.7 g/kg for virgin oils.