Refining can affect minor components
present in the unsaponifiable fraction of vegetable oils, such as PS. During
refining, the marker compounds, lupeol and compound X, are lost by 18 and 37%
in the esterified form, respectively, while losses of these two compounds in
the free form were 26 and 72%, respectively (171).
Total and esterified 4,4?-dimethyl sterols of the adulterated olive oil samples
were analyzed and the marker compounds traced by GC–MS. GC–MS analysis showed
that adulteration of olive oil with a sample of fully refined hazelnut oil could
be detected at a level as low as 2% by tracing lupeol in total or only in
esterified forms of 4,4?-dimethyl sterols (171).
Adulteration of expensive edible oils,
such as virgin olive oil, often involves desterolized oils to make the
adulteration difficult to detect. Sunflower oil contains characteristic ?7-sterols,
which are readily removed upon strong bleaching. It is shown that these ?7-sterols
do not primarily dehydrate (as do ?5-sterols), but isomerize to ?8(14)-
and ?14-sterols. For the detection of desterolized sunflower oil, it
is sufficient to analyze these compounds by HPLC or GC (110).
analysis of steradienes represents, in fact, a useful method for detecting the
addition of refined oil to extra virgin olive oils and is one of the official
methods in the European Union (135).
Elevated levels of steradiene hydrocarbons, especially stigmastadienes as they
are the most abundant in virgin olive oil can be a useful indicator of
adulteration with a refined oil (172).
All the different varieties of rapeseed,
including high erucic rapeseed, canola and specialty canola, contain moderate
amounts of brassicasterol, characteristic of Brassica oils. However, it
also occurs in other common edible vegetable oils but at extremely low levels.
Brassica is, thus, a marker to identify Brassica oils and to detect
adulterations of other oils with rapeseed and canola oils (44).
The low quality animal fats can be used
to adulteration of virgin coconut oil (VCO) because of some similarities such
as transparency to creamy white color and solid state at room temperature. A
new method has been developed based on the cholesterol level to detect the
presence 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 trimethylsilyl
ethers derived from cholesterol and cholestanol, so that the cholesterol
content in pure VCO and false VCO adulterated with animal fats could be
accurately determined. Determination of the cholesterol level in VCO could be
used 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).