Complex role of monoacylglycerols in the oxidation of vegetable oils: different behaviors of soybean monoacylglycerols in different oils.

The relationship between fatty acid composition of oils and their oxidative stability in the presence of monoacylglycerols was investigated. Purified vegetable oils were added at increasing amounts (0.5, 1, 2, and 3%) of monoacylglycerols obtained from purified soybean oil and submitted to an oven test (60 °C for 18 days). The obtained results showed a generally antioxidant effect of monoacylglycerols, with remarkable differences among oils. The antioxidant effect was significantly higher in less unsaturated oils, such as palm and olive oils. Among the more unsaturated vegetable oils, peanut and sunflower oils showed an almost linear slowdown of oxidation, slightly less pronounced in sunflower oil, which was the most susceptible to oxidation due to its high content of linoleic acid. A peculiar trend was highlighted for soybean oil, where the antioxidant effect of high amounts of monoacylglycerols was opposed to a pro-oxidant effect observed up to 1%.

Effects of monoacylglycerols on the oxidative stability of olive oil.

BACKGROUND: The study of pro- and anti-oxidant compounds is important for their influence on the shelf-life and nutritional value of food. The aim of this research was to evaluate the activity of monoacylglycerols (MAG), obtained by partial saponification of a purified olive oil, added in increasing amounts to the same oil and submitted to the Rancimat test and oven test at 60 °C. Besides routine analyses, high-performance size exclusion chromatography analysis of polar compounds was performed. RESULTS: The addition of MAG led in all cases to a significant slowdown of the oxidative processes. These trends were more evident as the oxidation went on. The purified oil added with 30 g kg(-1) of MAG after 9 days of oven test at 60 °C presented a level of oxidative degradation significantly lower than the control after only 4 days. CONCLUSION: The data showed a marked antioxidant effect of MAG in purified olive oil, contrary to what has been observed by other authors, who noticed either a pro-oxidant or a non-antioxidant activity of these compounds in soybean oil. A different behaviour of MAG during oxidation could depend on the different fatty acid composition of the oil matter they are added to.