A. Lanzon

The hydrocarbon fraction of virgin olive oil and changes resulting from refining

In numerous Spanish virgin olive oils, 6,10-dimethyl-1-undecene, various sesquiterpenes, the series ofn-alkanes from C14 to C35, n-8-heptadecene and squalene are the only less volatile components detected by gas chromatography in the hydrocarbon fraction. In oils from olives of the Arbequine variety, a series ofn-9-alkenes has also been found. In refined oils, notable features are the absence of the most volatile compounds and the appearance of other hydrocarbons produced during the refining process. Among these,n-alkanes, alkadienes (mainlyn-hexacosadiene), stigmasta-3,5-diene, isomerization products of squalene, isoprenoidal polyolefins coming from hydroxy derivatives of squalene and steroidal hydrocarbons derived from 24-methylene cycloartanol were identified. Physical refining produces larger amounts of degradation products and greater losses ofn-alkanes than chemical processing. Squalene is the major hydrocarbon component in all oils, both virgin and refined. The ranges of concentration for the different hydrocarbons found in Spanish virgin olive oils are presented.

Formation of stigmasta-3,5-diene in vegetable oils

Abstract The formation of stigmasta-3,5-diene (STIG) in vegetable oils from beta-sitosterol was investigated. Previously, analytical methods for STIG determination were developed and verified. For virgin olive oil and crude vegetable oils, the usual oil production processes (pressure, centrifuging and solvent extraction) and long term storage did not produce measurable amounts of STIG, except in the case of crude olive pomace oils where small quantities arose as a result of the high temperature applied to the solid residues during the drying operation. The influence on STIG generation of variables affecting the refining processes was studied. Although minor amounts of STIG appeared after only heating the oil, this compound was produced mainly during the bleaching earth treatment. The decoloration temperature and the bleaching earth activity were the most important variables involved in STIG formation. After deodorising, carried out under normal conditions, the refined olive oils retained measurable amounts of STIG. The refining of other vegetable oils with high beta-sitosterol content (such as sunflower, rapeseed and soya oils) also rendered considerable amounts of STIG. These results support the method based on STIG determination for detecting low percentages of refined vegetable oils in virgin olive oils and crude seed oils.