Multivariate models to classify Tuscan virgin olive oils by zone.

Abstract

In order to study and classify Tuscan virgin olive oils, 179 samples were collected. They were obtained from drupes harvested during the first half of November, from three different zones of the Region. The sampling was repeated for 5 years. Fatty acids, phytol, aliphatic and triterpenic alcohols, triterpenic dialcohols, sterols, squalene and tocopherols were analyzed. A subset of variables was considered. They were selected in a preceding work as the most effective and reliable, from the univariate point of view. The analytical data were transformed (except for the cycloartenol) to compensate annual variations, the mean related to the East zone was subtracted from each value, within each year. Univariate three-class models were calculated and further variables discarded. Then multivariate three-zone models were evaluated, including phytol (that was always selected) and all the combinations of palmitic, palmitoleic and oleic acid, tetracosanol, cycloartenol and squalene. Models including from two to seven variables were studied. The best model shows by-zone classification errors less than 40%, by-zone within-year classification errors that are less than 45% and a global classification error equal to 30%. This model includes phytol, palmitic acid, tetracosanol and cycloartenol.