Introduction
Taint in food is a significant cause of consumer rejection of food. Even if the food is safe in both the chemical and microbiological aspects, consumers will usually reject a food product that "doesn't smell right" or "tastes off". This can result in lost production, lost sales, lost consumer confidence, damaged brand names, damaged commercial relationships between supplier, manufacturer and retailer, and even expensive litigation. In addition, identifying the source of the taint can be time consuming and expensive, but is essential in preventing recurrences of the taint.

The ISO definition of taint is a "taste or odour foreign to the product". The term "taint" is normally reserved for unpleasant odours or flavours imparted to the food through external sources, whereas an "off-flavour" is usually used to describe unpleasant odours or flavours imparted to the food through internal deteriorative processes. It is important to emphasise that a taint or off-flavour exists if it is perceived by the human senses and no amount of chemical analysis, assurances by producers or denial statements will make it go away.

Taint Identification
Consumers are usually very good at detecting taints, but are notoriously inaccurate in describing them. Thus, the first step for an investigator is accurate identification of the chemical compound(s) responsible for the taint. Often these are highly odorous compounds present at very low levels; mg/kg (parts per billion) or ng/kg (parts per trillion). High sensitivity analysis is usually required to detect taint compounds in the complex food matrix - in some cases this can be like trying to find the proverbial needle in a haystack.

Fortunately a variety of techniques are available to selectively isolate taint chemicals from the complex food matrix. These include solvent extraction, headspace analysis, steam distillation, purge & trap, closed loop stripping, thermal desorption, vapour phase extraction and supercritical fluid extraction. The preferred method of final analysis for organic compounds is gas chromatography - mass spectrometry (GC-MS) which not only separates compounds but also identifies them by their mass spectral fingerprint. Sometimes the chemical or physical nature of the taint compound precludes the use of GC-MS, so alternative techniques ( e.g. HPLC, SEM, TLC, ICP, etc.) must be applied.

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