Precise classification of virgin olive oils with various linoleic acid contents based on triacylglycerol analysis

Thirteen samples of virgin olive oil (VOO) with different content (4–18%) of linoleic acid were subjected to a detailed triacylglycerol (TAG) analysis by silver-ion thin-layer chromatography (Ag-TLC) and densitometry. Direct quantitative determination of all TAG classes down to 0.1% without preliminary fractionation was performed. The major TAG classes plus a single peak containing the sum of minor polyunsaturated TAG (SPUTAG) were separated in a first run. Depending on the linoleic acid content of a sample the values of SPUTAG ranged between 4% and 13% of the total olive oil TAGs. In a second run all individual minor TAG classes were quantified as a part of SPUTAG. After common statistical processing of the multiple measurements for each sample, the SPUTAG levels and the values of the individual minor TAGs were used for the VOOs classification into three types. According to their linoleic acid content the three types were assigned as low (<6%), typical (6–10%) and high (>10%). The results for each minor TAG class are presented as mean values with the corresponding 95% confidence interval. The three types are clearly distinguished by the large differences between the mean values and the acceptably narrow confidence intervals. In high linoleic acid oils the D3 content regularly exceeds the upper limit of 0.5% accepted for VOOs by EC regulations [Commission of the European Communities; Regulation 2568/91; Regulation 1429/92; Regulation 183/93]. The postulated minor TAG compositions for “low”, “high” and especially for the “typical” types may be useful as a criterion for authenticity of genuine olive oils.