Effect of some terpenyl oleates on soybean oil oxidation at 180○C

The ability of linalyl oleate (LO) to act as an autoxidation inhibitor in soybean oil at 180 +/- 5 degrees C was compared with the oleates of geraniol (GeO), menthol (MenO), perillyl alcohol (PeO), farnesol (FaO), phytol (PhO), and cholesterol (ChO) at levels of 0.1% by weight in the oil. Changes in FA composition and conjugated dienes were monitored. Logarithmic plots of the decreasing ratios of linoleate/palmitate and linolenate/palmitate vs. time were linear for soybean oil controls, but plots for LO, GeO, MenO, PeO, FaO, and ChO had inflection points (IP) at times betvveen 5 and 11.4 h. These terpenyl oleates had smaller rate constants before the IP than the control oil. Thus, these esters all exhibited autoxidation inhibition, which was confirmed by conjugated diene values. Plots for PhO had no IP and very limited inhibitory effect relative to the controls. LO originally was chosen for study because it has a double bond structure similar to that of the side chain of avenasterol, which also shows an ability to inhibit oxidation. The ability of terpenyl oleates having widely different structures to inhibit autoxidation suggests that LO's double bond structure is not the cause of its inhibitory activity.