QUALITY AND AUTHENTICITY ASSESSMENT OF FISH AND CAVIAR BY FATTY ACID,STABLE ISOTOPE AND FLAVOUR PROFILES

International fish trade is nowadays strongly influenced by food authenticity and safety norms, and several European Directives have introduced aspects concerning quality and safety standards into the fish chain. These regulations were aimed to provide consumers with a minimum of information on the origin of these products. It is well documented that farming conditions and dietary treatments can largely modify aquaculture products. On the basis of this consideration, several studies have been published to investigate the potential of different analytical tools in distinguishing wild and farmed fish. Classically, this was carried out using scale pattern analysis and morphological characteristics or a combination of both methods. More recently, many analytical procedures have been applied for this purpose, ranging from the determination of carotenoid stereoisomers to the use of fatty acid profile and compositional analysis as well as to the quantification of different levels of organic contaminants, in conjunction with statistical multivariate analysis. According to these considerations, the aim of the first trial of the present work was to study the potential application of fatty acid analysis and IRMS of carbon and nitrogen in the muscle tissue of wild and farmed turbot to discriminate the production method and the geographical origin of fish. Both linear discriminant analysis (LDA) and soft independent modeling of class analogy (SIMCA) were applied to the data as classification tools. For this purpose, 30 wild turbot from Spain and 30 farmed turbot from Denmark and The Netherlands were collected. The application of linear discriminant analysis (LDA) and soft independent modeling of class analogy (SIMCA) to analytical data demonstrated the combination of fatty acids and isotopic measurements to be a promising method to discriminate between wild and farmed fish and between wild fish of different geographical origin. In particular, IRMS (Isotope Ratio Mass Spectrometry) alone did not permit us to separate completely farmed from wild samples, resulting in some overlaps between Danish wild and Spanish farmed turbot. On the other hand, fatty acids alone differentiated between farmed and wild samples by 18:2n-6 but were not able to distinguish between the two groups of wild turbot. When applying LDA isotope ratios, 18:2n-6, 18:3n-3, and 20:4n-6 fatty acids were decisive to distinguish farmed from wild turbot of different geographical origin, while delta(15)N, 18:2n-6, and 20:1n-11 were chosen to classify wild samples from different fishing zones. In both cases, 18:2n-6 and delta(15)N were determinant for classification purposes. The second trial was designed to characterize and typify caviar obtained from farmed white sturgeons (A. transmontanus) fed two experimental diets containing different dietary lipid sources by chemical composition, fatty acids and flavour volatile compounds. Twenty caviar samples from fish fed two experimental diets containing different dietary lipid sources have been analysed for chemical composition, fatty acids and flavour volatile compounds. Fatty acid make up of caviar was only minimally influenced by dietary fatty acid composition. Irrespective of dietary treatments, palmitic acid (16:0) and oleic acid (OA, 18:1n-9) were the most abundant fatty acid followed by docosahexaenoic acid (DHA, 22:6n-3) and eicopentaenoic (EPA, 20:5n-3). Thirty-three volatile compounds were isolated using simultaneous distillation–extraction (SDE) and identified by GC–MS. The largest group of volatiles were represented by aldehydes with 20 compounds, representing the 60% of the total volatiles. n-Alkanals, 2-alkenals and 2,4-alkadienals are largely the main responsible for a wide range of flavours in caviar from farmed white surgeon. The present trial shows that the overall nutritional and organoleptic qualities of caviar obtained from fish fed significantly different diets (marine oil vs. vegetable oil) was almost unaffected.