HS-SPME-GC-MS analysis towards supporting the panel test: quantitation of VOCs in Virgin Olive Oils

Rancid is one of the most widespread olive oil defects. It is due to oxidative phenomena that affect free unsaturated fatty acids leading to the formation of unpleasant volatile molecules. The nature and the amount of these molecules are not yet satisfactorily defined, mainly due to the high complexity of the oil profiles, the different odour threshold of the molecules and the possible synergistic and/or antagonistic effect between them. The main risk factors for rancidity develop are damaged or overripe olives and oil oxidation during storage, and the principal pro-oxidative factors during olive oil storage are exposure to light and oxygen. This work started by a collaboration between Carapelli Firenze and the University of Florence and is aimed to better understand how the unpleasant molecules origin and how they affect the virgin olive oil sensory quality. To this goal we selected two extra virgin olive oils differing for their fatty acid composition (at low and high oleic acid percentage). The oils were analyzed from both chemical and sensorial point of view; each ,was divided in several aliquots and stored up to six months in different conditions (under light exposure or in the darkness, in presence or in absence of oxygen). Samples collected at each storage time were subjected to sensory and chemical analyses (i.e. free acidity, peroxide number, spectrophotometric indexes, volatile compounds, phenolic compounds chlorophylls and carotenoids). The second step was to select more than one hundred virgin olive oils or extra virgin olive oils, already subjected to sensorial analysis, to define their volatile fraction by a validated HS-SPME-GC-MS method [1]. The intensity of rancidity was then correlated to the amount of different sub-groups of volatile compounds, and some chemical indexes for the olive oil rancid defect were proposed and tested with a further set of virgin olive oils.