If food flavour is not as expected, it can damage consumer confidence and give the perception of poor quality. Setting analytical standards of what constitutes an acceptable flavour can be challenging, and while methods based on total volatiles or specific marker compounds can be a useful quality control check, a more investigative approach is often required. Determination of the taints and off-flavours responsible can be particularly challenging as the compounds are often unknown and may be present at extremely low levels (sub ppb). This article discusses the analytical methods available for taint and flavour analysis and highlights the approaches taken to identify compounds responsible and determine root cause.
Taints and off-flavours in food represent poor quality to the consumer and result in lack of confidence and brand damage. Analysis is performed to determine the source of the issue, to ensure consumer safety, and to prevent future occurrence. Food taint determination is challenging, because the matrix is complex and the compounds responsible may only be present in food at extremely low levels. If key aroma or taste compounds are known, analysis can be targeted when characterizing flavour, but determining taints and off-flavours requires a more investigative approach. Evidence must be gathered about a particular issue and the analytical data be connected with sensory characteristics. A term used frequently in analytical chemistry is "fit for purpose." For targeted analysis, where compounds are known and required limits of detection are clear, this is relatively easy to define. However, for unknown contaminants, at undefined levels, optimization of methods can be more of a challenge.
ApproachesDetermination of food taints is not easy. Care must be taken to avoid possible contamination from external laboratory sources (including personal care products used by the analysts). To avoid contamination use a dedicated analysis area; handle and store all samples (controls, suspect samples, and reference standards) separately; and take care during transportation to the laboratory. It is also important not to alter the sample during extraction — particularly when analyzing off-flavours — so it may be necessary to avoid heating the sample.
It may be possible to use a targeted approach for taint determination if, for example, the source of contamination is known. However, a generic screening approach is most often used. In this case analysts can compare samples to control or reference samples to identify differences, rather than identify all volatile components in what can be a very complex sample.
For flavour analysis there are several possible approaches. A complete volatile profile can tell you much of the components in a sample, but different sample preparation methods will produce different profiles. It is also important to consider whether a more targeted approach is appropriate. A sample may have a very complex volatile profile, but only a few compounds may be key to the perceived characteristic flavour. It may therefore only be necessary to monitor the levels of these key compounds. Setting specifications for flavours, particularly natural ones, is rarely straightforward. A good understanding of acceptable levels of natural variation is required, and must always be linked to sensory data.
Consumer Perception and Sensory Evaluation
When taints or off-flavours are brought to light via consumer complaints, descriptions of the odour or taste are frequently unreliable or unhelpful. The first stage when investigating complaints should therefore be a sensory assessment of the sample — be that by an in-house specialist trained sensory panel or a more informal round table discussion — that will give objective assessments and sensory descriptors that can be matched to reference guides (1,2,3) or specialized websites ( http://www.odour.org.uk/ and http://www.flavornet.org/).
Sensory analysis is key to quantitative methods of analysis as an accurate description can provide key information to the analyst. However, very similar compounds can have very different sensory thresholds and even isomers can be perceived very differently in terms of levels needed to give a taint. Other components within the food matrix can also affect acceptability and potency of flavour compounds. This is further complicated as more than one compound may be responsible for the taint.
Sensory theory perception is therefore used in combination with chemical analysis, rather than as a stand-alone method, to confirm the identity and levels of the compounds present.