Hiroshi Onishi

Studies on Osmophillic Yeasts

Influences of concentrations of sodium chloride and pH values of soy mash on the changes of microflora during the ripening process were investigated. The proportions of various yeasts in the soy mash were proved to be changed with the above two environmental factors. And it was shown that growth sequence of yeasts in soy mash was controlled according to their pH sensitivities at the hypertonic condition. From young soy mash (3 days’ old), the following yeasts were isolated: salt-tolerant type.…Saccharomyces rouxii Boutrpux, Torulopsis famata (Harrison) Lodder et Kregervan Rij, Candida polymorpha Ohara et Nonomura, Pichia farinosa (Lindner) Hansen, and Trichosporon behrendii Lodder et Kreger-van Rij ; salt-sensitive type.…Candida tropicalis (de Beurm., Gougerot et Vaucher) Ota and Candida rugosa (Anderson) Diddens et Lodder.

Studies on Soy Yeasts

(1) The author studied on methods for determining viable counts of yeasts in the presence of molds such as Koji-molds. (2) As it was difficult to differentiate yeast cells from the spores of the molds under micros-cope, plate culture method was adopted. (3) By anaerobic plate culture (duplicate dishes method) growth of molds could be inhibited and growth of yeasts, especially pellicle forming ones, was also inhibited to some extent. Moreover, this method was shown to be inconvenient to count the exact number of yeasts owing to the cracking of the media by the production of gas. (4) Antifungal agents which do not inhibit the growth of yeasts were investigated. And sodium propionate was found to be comparatively effective for that purpose. Its antifungal activity increased with the lowering of the pH of the medium in a certain extent. The plate culture using Koji extract agar added with sodium propionate by 0.2% and pH 4.6 was revealed to be most suitable for determining the viable counts of soy yeasts.