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of oils, but these should be within acceptable limits judged by the experience of the
assessor. Many of the commercially available essential oils originate in countries
remote from those in which they are used so that control is of prime importance in
both the selection and acceptance of these materials, particularly for use in food
products.
Routine physical tests include
∑ moisture content (ISO 939-1980)
∑ specific gravity/relative density
∑ optical rotation
∑ refractive index
∑ freezing or congealing point
∑ solubility in diluted alcohol of a stated strength (a table for the preparation of
diluted alcohol is given in British Standard BC 2073: 1976).
Chemical tests include
∑ acid value
∑ ester value before acetylation (for calculation of esters and combined alcohols)
∑ ester value after acetylation (for calculation of free alcohols)
∑ ester value after formulation (for calculation of free tertiary alcohols)
∑ carbonyl value
∑ phenol content.
There are specific tests which should only be used in commercial transactions after
full agreement by both parties. In any event, the method employed must be clearly
indicated in the test report. Test methods are defined in food chemicals codex III for
determination of:
∑ acetals
∑ acid value
∑ total alcohols
∑ aldehydes
∑ aldehydes and ketones
–hydroxylamine method
–hydroxylamine-tert butyl alcohol method- neutral sulfite method
∑ chlorinated compounds
∑ esters
∑ linalool content
∑ phenols, free phenols,
∑ residue on evaporation
∑ solubility in alcohol
∑ volatile oil content.
Industrial methods use chromatographic techniques (TLC, paper chromatography,
GLC (Humphrey, 1973), column chromatography, HPLC (Lego, 1984));
spectrophotometric techniques (visible range, UV range, IR range) and spectroscopic
methods (NMR, mass spectroscopy (MS), usually coupled with GLC (Thomas, 1984)).
Kumar and Madan (1979) have described a rapid method for the detection of adulteration
in essential oils using an iodide monobromide/mercuric acetate to establish iodine
values which can be directly compared with those for genuine oils.