Improvement of Flavor of Cultured Oyster

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Oyster is one of Popular seafoods in Japan as well as in many other countries. However, the Production and consumption of the European Flat oyster, Ostrea edulis, are very Limited in Japan. For the purpose of increasing the consumption of the cultured oystes, the present research aimed at the improvement of its Flavor by feeding phytoplankton or formula food.1. Four groups of European flat oyster were reared on each of two species of diatom, Chaetoceros gracilis (C.g group) and Nitzschia closterium N.c group), a haptophyte, Isochrysis galbana (I.g group) and a formula feed (RL group) for 30 days in tanks. The control group was kept in the sea.2. In the sensory tests of edible parts, many panelists answered that the I.g group was better than the control group in sweetness, umami and astrigency, indicating that the former was more acceptable than the latter. The C.g, N.c and Rl groups were judged to be inferior to the control group in texture, odor and saltiness.3.The contents of glycogen in the 4 test groups were considerably lower than that of the control group. I.g group was rich in taurine, glycine and glutamic acid. Alanine and glycine were markedly poor in the'C.g and N.c groups.4. The levels of saturated, monounsaturated and polyunsaturated (PUFA) fatty acids were 32-34%, 15-21%, 47-52% of total fatty acids, respectively, in the 5 groups. The percentage of PUFA was the lowest in the Rl group, which showed also lower level of n-3 series fatty acids but higher n-6 ones than the other groups.5. The toughness of digestive organs as measured with a plunger was 42 g/mm^2 for the N.c group and 27-29 g/mm^2 for the other groups. As for the protein composition of digestive organs of the 5 groups, the water-soluble, salt-soluble, alkali-soluble and insoluble fractions were 35-53%, 21-33%, 18-26% and 5-6%, respectively. No correlation was observed between the texture and protein composition.