The effect of algae diets (Skeletonema costatum and Rhodomonas baltica) on the biochemical composition and sensory characteristics of Pacific cupped oysters (Crassostrea gigas) during land-based refinement

Oyster refinement, a common practice in France, is aimed at increasing the weight of oyster tissue and influencing the taste properties of the refined oysters. Refinement usually takes place in land-based systems where the oysters are fed with relatively high concentrations of microalgae. In this study the impact of feeding Skeletonema costatum and Rhodomonas baltica on the biochemical composition and sensory characteristics of Pacific cupped oysters (Crassostrea gigas) from the Eastern Scheldt during land-based refinement was studied. After a feeding period of four and seven weeks market-sized oysters were sampled for the analysis of fatty acids, free amino acids and volatile organic compounds and for a sensory evaluation by consumers and an expert panel. The algae Skeletonema costatum showed a lower Sigma PUFA, Sigma n - 3, En - 6, C18:2n6, C18:3n3, C18:4n3, C22:6n3 content as compared with Rhodomonas baltica. These differences were also reflected in the fatty acid profile of the oysters fed with the corresponding algae diets. Furthermore, general linear model and principal component analysis showed marked differences in free amino acids and volatile organic compound content between Skeletonema, Rhodomonas fed oysters and reference oysters. For example, threonine, glutamine, leucine, histidine, (E)-2-hexenal, (E)-2octenal, (E)-2-octen-1-ol, (E,E)-2,4-octadien-l-ol, (E,Z)-3,6-nonadien-1-ol and (Z,E)-2,6-nonadienal contents were higher in Skeletonema fed oysters compared to Rhodomonas fed oysters. Sensory differences between the experimental oyster groups were shown. Skeletonema fed Pacific cupped oysters were characterized by a stronger seaweed flavor, higher perceived sweetness and a firmer texture in comparison with Rhodomonas fed oysters. Naive consumers were only able to differentiate between Rhodomonas fed oysters and reference oysters.