Refining can affect minor componentspresent in the unsaponifiable fraction of vegetable oils, such as PS. Duringrefining, the marker compounds, lupeol and compound X, are lost by 18 and 37%in the esterified form, respectively, while losses of these two compounds inthe free form were 26 and 72%, respectively (171).Total and esterified 4,4?-dimethyl sterols of the adulterated olive oil sampleswere analyzed and the marker compounds traced by GC–MS. GC–MS analysis showedthat adulteration of olive oil with a sample of fully refined hazelnut oil couldbe detected at a level as low as 2% by tracing lupeol in total or only inesterified forms of 4,4?-dimethyl sterols (171).Adulteration of expensive edible oils,such as virgin olive oil, often involves desterolized oils to make theadulteration difficult to detect. Sunflower oil contains characteristic ?7-sterols,which are readily removed upon strong bleaching. It is shown that these ?7-sterolsdo not primarily dehydrate (as do ?5-sterols), but isomerize to ?8(14)-and ?14-sterols.
For the detection of desterolized sunflower oil, itis sufficient to analyze these compounds by HPLC or GC (110).Theanalysis of steradienes represents, in fact, a useful method for detecting theaddition of refined oil to extra virgin olive oils and is one of the officialmethods in the European Union (135).Elevated levels of steradiene hydrocarbons, especially stigmastadienes as theyare the most abundant in virgin olive oil can be a useful indicator ofadulteration with a refined oil (172).All the different varieties of rapeseed,including high erucic rapeseed, canola and specialty canola, contain moderateamounts of brassicasterol, characteristic of Brassica oils. However, italso occurs in other common edible vegetable oils but at extremely low levels.Brassica is, thus, a marker to identify Brassica oils and to detectadulterations of other oils with rapeseed and canola oils (44).The low quality animal fats can be usedto adulteration of virgin coconut oil (VCO) because of some similarities suchas transparency to creamy white color and solid state at room temperature. Anew method has been developed based on the cholesterol level to detect thepresence of animal fats in VCO.
It has been demonstrated that the comprehensive two-dimensional gas chromatography (GC× GC) could obtain a complete baseline separation of the sterol trimethylsilylethers derived from cholesterol and cholestanol, so that the cholesterolcontent in pure VCO and false VCO adulterated with animal fats could beaccurately determined. Determination of the cholesterol level in VCO could beused for reliable detection of lard, chicken fat, mutton tallow, beef tallow,or their mixture in VCO at a level as little as 0.25% (173).