| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1994: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1993: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
Osmophilic yeasts are known to cause spoilage of drying, sugaring or salting foods. Particulary in Japan, spoilage of soy sauce or miso paste by an osmophilic yeast, Zygosaccharomyces rouxii, has been a long-pending problem in their production and preservation processes. Though the yeast is essential to the ripening stage of soya sauce or miso paste, a wrinkled pellicle-forming strain of the yeast appears when the salt content becomes high. Thus far, there are no chemicals pracically applicable for prevention of the pellicle formation. Moreover Biochemical and physiological analyzes of the pellicle formation by Z.rouxii are limited. This study has been set up to find new natural inhibitors against the pellicle formation, and to approach to the mechanism of pellicle formation.
To find natural inhibitors, we first established bioassay systems tested on an agar plate. One system is a convenient method (paper disc method) examining the haloing zone around the paper disc containing inhibitor
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, and another is a more quantitative method (direct-color reflection method) measuring reflection potency of the yeast colony by a colometer. Using the paper disc method, we found an extract of Demodium caudatum to inhibit the pellicle formation of the strain, Z.rouxii F51. This plant is interestingly known to have been used for preservation of miso paste. By combination of several chromatography, two major inhibitors, DGDG (1,2-di-O-linolenoy1-3-o-digalactosyl-sn-glycerol) and MGDG (1,2-di-O-linolenoy1-3-0-glalctosyl-sn-glycerol) were isolated from the extract. MGDG was shown to be more active than DGDG by the direct-color reflection method. Furthermore, inhibitory activities of plant-derived glyceroglycolipids including DGDG and MGDG were higher than those of synthetic detergents, commonly known inhibitors. The glyceroglycolipids level in the leaf of D.caudatum becomes high in June, then gradually lowers, and again increases to reach maximum in November. The climatic condition of June is most fit for the yeast to grow. Then, the leaves of D.caudatum may have been used in this season.
Major cell-wall components was compared between pellicle forming and non-forming yeasts. In particular, oleic and Iinolenic adids were highly accumulated in the pellicle forming yeast. Thus, it may be possible to approach to the mechanism of pellicle formation from the point of fatty acid metabolism of Z.rouxii. Less
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