Studies on the Production and Improvement of Flavors of Fishes and Shells in Microalgae

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In this study, we concentrated to make clear the biosynthesis and role of volatile sulphur compound, especially dimethylsulphide, in microalgae and macroalgae. The major source of dimethylsulphide in the aquatic environment appears to be the enzymatic cleavage or alkaline degradation of dimethyl-beta-propio thetin into dimethylsulphide and acrylate. The dimethylsulphide producers are chlorophyta (such as Ulva and Enteromorpha), rhodophyta (such as Polysiphonia), haptopyta (such as Emiliania and hymenomonas) and dinophyta (such as Gymnodinium, Gyrodinium, and Crypthecodinium). This dimethylsulphide fills the role originally assigned to H2S ; that of transferring sulphur from the seas through the air to land surface, and is very likely the compound most responsible for the characteristic "odor of the sea" or "flavour of sea weeds".We established the growth condition of Crypthecodinium cohnii (dinoflagellate) to get high cell yield (12g wet weight/L).From the relationship between the stru … More ctures of methionine, dimethyl-beta-propiothetin and dimethyl-sulphide, our recent study make clear that, in C. Cohnii, the methyl group and the sulphur of dimethyl-beta-propiothetine are derived from the methyl group and the sulphur of methionine and that the carboxyl group of methionine is not incorporated. We showed the crude extracts of C. Cohnii had methionine decarboxylase activity and did not have methionine deaminase activity. The observation are consistent with the hypothesis that methionine is converted to 3-methylthiopropylamine by decarboxylation and that 3-methylthiopropylamine is converted to dimethyl-beta-propiothetin by deamination, oxidation and methylation, and that the carboxyl group of dimethyl-beta-propiothetine may arise from the 2-carbon of methionine.We also found that the precursor of dimethylsulphide, dimethyl-beta-propiothetin, greatly accelerates the biting behaviors of goldfish, carp, crucian carp and tilapia. Dimethyl-beta-propiothetin proved not only to be an effective stimulant for the striking behavior of fishes but also to be able to promote fish growth. A crude extract of Crypthecodinium cohnii and its main component, dimethyl-beta-propiothetin, significantly and dose dependently protected the gastric mucosa against HCI-ethanolーinduced lesions in rats. Since indomethacin pretraetment reduced the protective effect to some extent, endogenous prostaglandins might be partly involved in the mechanism of action. Both the crude extract and dimethyl-beta-propiothetin significantly increased gastric secretion.The volatile components of Crypthecodinium cohnii were investigated to find its pleasant flavour compounds that could be associated with some edible seashore products. Heating the fresh wet alga with glass beads gave 66 volatile components. The first intact distillate greatly contained dimethylsulphide nearly 99%. Other components included some strong sweet-odorus compounds ; 2ーhydroxy-3-methy1-2-cyclopenten-l-one (cyclotene), 2, 5-dimethyl-4-hydroxy-3 (2H) -furanone (furaneol), and 3-hydroxy-2-methyl-4H-pyran-4-one (maltol). Less