Identification and characterisation of off-flavours in foods by means of integrated sensory
and PME/GC-MS analysis
By Andrea Giomo, Eurofins Qualis, Italy
Some substances give food an unpleasant negative sensation in humans. It is therefore necessary to have an objective method for their identification and characterisation in order to quickly solve problems in food production.
Eurofins Qualis is offering an integrated package of ISO 13299:03 sensory profile techniques and solidphase microextraction/ gas chromatographic-mass spectrometric analysis (SPME/ GC-MS) which is proving very effective as illustrated by the following examples:
A factory producing breadsticks experienced frequent complaints of an unpleasant smell in their breadsticks. The sensory profile technique identified the real significant descriptor as “rancid”. Subsequent headspace gas analysis showed that the molecule that correlated with the characteristics of “rancid” was hexanal (see illustration). Once identified as the problem, the experts could check the manufacturing process: In the production of vegetable fats for the baking industry, a certain proportion of vegetable oil (high in polyunsaturated fatty acids) is used, as well as palm oil derivatives (saturated fatty acids). In the processing of the breadsticks, any dough left over was placed in containers and used at the end of the day as “rework” material. Whilst in the container awaiting use, the room temperature activated the enzyme lipoxygenase which lead to the breakdown of linoleic and linolenic fatty acids into hexanal and other similar molecules. This produced the unpleasant rancid odour in the breadstick.
Similarly, a significant number of consumers complained about an unpleasant odour in a famous brand of organic chocolate bars. The sensory laboratory identified the characteristic descriptors for both “acceptable” and “defective” samples. The chemical laboratory analysed the headspace of these samples using SPME/ GC/MS to identify the differences and hence the “significant” odorous molecules. From the information obtained it was possible to assign the corresponding odorous molecule to the description identified in the organoleptic analysis using statistical methods. Using this technique, it was determined that the “bad smell” was caused by an amide, a derivative from fermentation probably formed during the drying phase of cocoa nibs in the country of origin of the raw material.
If you would like assistance with such issues, please contact your local Eurofins representative or the author.
Contact: andreagiomo@eurofins.com