Characterization of the Key Odorants in High-Quality Extra Virgin Olive Oils and Certified Off-Flavor Oils to Elucidate Aroma Compounds Causing a Rancid Off-Flavor

To identify the odorants responsible for a rancid off-flavor in olive oils, first, the key aroma compounds in a premium extra virgin olive oil (PreOO1) were characterized by the sensomics approach and were then compared to those present in a certified rancid off-flavor olive oil (RanOO1) obtained from the International Olive Council (IOC). By application of an aroma extract dilution analysis, 46 odorants were detected and subsequently identified in PreOO1 and 35 odorants in RanOO1, respectively. After quantitation by stable isotope dilution assays, calculation of odor activity values (OAVs; ratio of concentration to odor threshold) revealed only 5 odorants with OAVs > 10 in PreOO1, while 13 odorants showed OAVs > 100 in RanOO1, with (E,Z)-2,4-decadienal, hexanoic acid, octanal, hexanal, (E)-2-octenal, and (Z)-2-nonenal being among the most odor-active compounds. Thus, marker aroma compounds for this off-flavor type could be suggested. Additionally, based on the OAVs obtained, the overall aroma profiles of both oils were mimicked by aroma recombination experiments. As proof of concept, 16 marker odorants were quantitated in two additional extra virgin olive oils and in eight further olive oils eliciting a rancid off-flavor. Application of a principal component analysis (PCA) and a hierarchical cluster analysis successfully discriminated both categories of olive oils. In the 12 olive oils used, acetic acid showed the highest Pearson coefficient between the perceived intensity of the rancid defect and the odorant concentration. In particular, (E,Z)- and (E,E)-2,4-decadienal and (Z)-2-nonenal can be suggested as chemical markers for olive oil rancidity in combination with positive aroma markers, for example, acetaldehyde and (Z)-3-hexenal.