The presence of urease inhibitor was suggested in previous studies on the removal of urea in commerial sake by
Zoogloea urease.
Therefore, the nature and origin of inhibitor present in sake were now examined. Ultrafiltration with the cut-off molecular weight of 10, 000 dalton had no effect on the inhibition. The inhibitor had negative charge and its inhibition was reversible. Organic acids contained in sake did not inhibit the urease activity. It was revealed that fluoride was the major inhibitor to
Zoogloea urease in sake. Concentrations of fluoride in sake were in good agreement with degrees of inhibition, and the fluoride concentration giving 50% inhibition was O.1 ppm. A fairly good correlation between concentrations of fluoride in sake and those in water suggested that fluoride present in sake was derived from water used in sake-production. Fluoride was effectively removed from water by ionexchange or alumina treatment, and sake produced with fluoride-removed water showed only little inhibition on the treatment with
Zoogloea urease.
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