Waxes and olive-residue oil

Long chain aliphatic esters, commonly called waxes, are components of epicuticular waxes of the olive fruits (Bianchi and Vlahov, 1994). Whilst in virgin olive oils the wax concentration is negligible, in olive-residue oil the wax content is considerable. Thus, the presence of long chain esters in olive oil is evidence of the presence of solvent extracted olive oil, also commonly called sansa olive oil. The detection and quantification of waxes in olive oil is an official method. As shown in Table 2.2, virgin olive oils fit for consumption must contain less than 250 mg/kg of waxes the limits are 350 mg/kg for categories 4,5 and 6, whilst for olive-residue oil the amount is expected to be over 350 mg/kg. 

Studies on the chemical structure of olive wax esters have shown that the homologues present in olive-pomace oil are almost entirely esters of oleic acid with long chain alkanol constituting the homologous series C40, C42, C44, C46. Odd-chain esters identified in the oil were esters of oleic acid with C23, C25, C27 alcohols. Gas chromatography and mass spectrometry analysis has shown that each carbon chain of the esters in made up of a single isomer in which the acyl moiety is that of oleic acid (Bianchi el al., 1994). Thus, for example, ester C44 was found to be made up of the couple acid-alcohol Cl8 1 and C26, whereas other possible isomers such as C16 l-C28 were not detected. This is unusual if it is compared with the composition of epicuticular ester fractions of oil seeds for which, in cases studied, each ester chain was composed of several positional isomers of the ester group. 

This finding may represent a useful element for the further improvement of this analytical method, which would possibly permit the detection of olive oil sophistication with seed oils. 

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