Differentiation of fresh and frozen/thawed fish, European sea bass (Dicentrarchus labrax), gilthead seabream (Sparus aurata), cod (Gadus morhua) and salmon (Salmo salar), using volatile compounds by SPME/GC/MS.

Background: A simple method based on solid phase microextraction/gas chromatography/mass spectrometry (SPME/GC/MS) was applied for studying the volatile profiles of whole fish samples of European sea bass (Dicentrarchus labrax) and gilthead seabream (Sparus aurata) and fillets of cod (Gadus morhua) and salmon (Salmo salar) during frozen storage in order to be able to differentiate a fresh product from one that has been frozen. Analysis of volatile compounds was performed on these two product types, fresh and after freezing/thawing following storage at - 20 °C for 30 and 90 days.
Results: More than a hundred volatile compounds were found by SPME/GC/MS. Statistical processing by principal component analysis and ascending hierarchical classification was used to classify the samples into categories and verify the possibility of separating fresh samples from those that had been frozen and thawed. The compounds to be used as differentiators were identified. Four compounds were common to all species: dimethyl sulfide, 3-methylbutanal, ethyl acetate and 2-methylbutanal. Not only were they found in larger quantities after thawing but they also increased with the duration of storage at - 20 °C.
Conclusion: These four compounds can therefore be considered as potential markers of differentiation between a fresh product and one that has been frozen.
(Copyright © 2012 Society of Chemical Industry.)