Changes in the volatile composition of virgin olive oil during oxidation: Flavors and off-flavors

A thermoxidation process has been applied to extra-virgin olive oil to develop new knowledge on the evolution of the volatile compounds responsible for virgin olive oil flavor during oxidative deterioration. The initial volatiles (a total of 60), many of them responsible for the pleasant sensory characteristics of the oil and produced mainly through biochemical pathways, disappeared in the first hours, and the formation of off-flavors, produced through oxidative pathways, gradually increased. The main volatile compounds possibly responsible for off-flavors (51) were identified, and their evolution during the oxidative process was studied. The fatty acids content was determined during the process. Unsaturated fatty acids were found to be the main precursors of the volatile compounds found in oxidized samples. The early measurement of nonanal (which was not detected at all, or only at trace levels, in extra-virgin olive oil samples) could be an appropriate method to detect the beginning of the oxidation. The ratio hexanal/nonanal was used to differentiate between oxidized and good-quality virgin olive oil samples. Sensory evaluation of the samples and peroxide value agreed on the evolution of the oxidation.