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 resp onsible for virgin olive oil flavor during oxidative deterioration. Th e initial volatiles (a total of 60), many of them responsible for the pleasant sensory characteristics of the oil and produced mainly throug h biochemical pathways, disappeared in the first hours, and the format ion of off-flavors, produced through oxidative pathways, gradually inc reased. The main volatile compounds possibly responsible for off-flavo rs (51) were identified, and their evolution during the oxidative proc ess was studied. The fatty acids content was determined during the pro cess. Unsaturated fatty acids were found to be the main precursors of the volatile compounds found in oxidized samples. The early measuremen t 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 d etect the beginning of the oxidation. The ratio hexanal/nonanal was us ed 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.