Adulteration of vegetable bulk oils

5 Adulteration of vegetable bulk oils (coconut, cottonseed, grapeseed, maize, palm, palm kernel, peanut, safflower, sesame and sunflower) 

The above shows that rapeseed oil can easily be detected, or eliminated, as a contaminant by sterol analysis. It is also, at least in Europe, the oil most likely to be used to dilute another oil. Although low levels (as a percentage of the total sterols) have been reported in some other oils (Desbordes etal., 1993), the presence of brassicasterol in an oil is good evidence of contamination in any oil from a non-Brassica species. It is likely that the traces reported as present in some other oils arise from contamination of the sample with rapeseed oil, or from some other Brassica species, or from traces of some similarly behaving non-sterol not fully separated from the sterol fraction during the work-up of the sample (Desbordes et al., 1983). 

If the fatty acid composition is within the accepted range for the oil, then other analyses should be carried out. Those used will vary with the oil. If the oil being examined is maize, then the carbon isotope ratio should be examined. This is carried out by burning the oil and determining the ratio of 13C to 12C. From this it is possible to detect 10% or above of an oil other than maize (Rossell, 1994). 

Sterol analysis can be useful other than for detecting rapeseed oil. Accepted ranges for many oils and all major oils, given as a percentage of the total sterols, are available (Codex Alimentarius, 1997 FOSFA, 1994 AOCS, 1997). In all 

It is claimed (Youk et al., 1999) that olive, sunflower and peanut oils contain mainly esterified sterols, while soyabean and sesame oils contain mainly free sterols. This does not appear to have been utilized previously, but could be useful with mixtures of the two classes. Although it is possible to de-sterolize oils, and remove characteristic sterols, this usually forms other sterols that can be detected (Biedermann and Grob, 1996 Lanuzza and Micali, 1997 Mariani and Venturini, 1997). If it is suspected that this has occurred, then the presence of other suspect components should be investigated. 

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