IDENTIFICATION AND CHARACTERIZATION OF FI LM-FORMING YEASTS ISOLATED FROM DECOMPOSING SALTED UME-PROCESSED PRODUCTS

Salted ume fruit (Japanese Apricot, Prunus mume Sieb. et Zucc. var. mi crocarpa Makino) is one of the traditional food produced in Japan. Two kinds of salted ume-processed products, 'Ume-boshi' and 'Ume-zuke' ar e known. There is currently great importance for the prevention of con tamination with film-forming yeasts on 'Ume-boshi' and 'Ume-zuke' in t he recent trend of reducing salt content in foods. So, we investigated on the ingredient changes of products contaminated with film-forming yeasts. And, isolation, identification and characterization of contami nated yeasts were performed. According to the progress of contaminatio n with yeasts, organic acids chiefly contained in salted ume-processed products were observed a significant decrease, by which the pH risen. And, the hardness of the flesh of a ume fruit of 'Ume-zuke' deteriora ted and pectin related compounds were decomposed. It was suggested tha t these loss of organic acids and decomposition of pectin related comp ounds were mainly caused by contaminated yeasts. Seventy five of yeast s strains were obtained by isolation and purification of yeast strains from decomposing products contaminated with yeasts. Respective twenty five isolates were identified on the basis of standard morphological and biochemical tests as strains of Debaryomyces hansenii (4 isolates) , Pichia anomala (I isolate), Pichia membranaefaciens (3 isolates), To rulaspora delbrueckii (1 isolate), Kloeckera apiculata (2 isolates), C andida famata (1 isolate), Candida krusei (3 isolates), Candida pellic ulosa (3 isolates) and other unidentified Candida sp. (7 isolates) des ignated as Candida sp. UME-A, Candida sp. UME-B and Candida sp. UME-C. As the results of characterization of yeasts isolates, strains of C. fatama, Candida sp. UME-A, Candida UME-B showed a high salt tolerance (halophilic) which could grow in YM liquid media contained 20% NaCl an d showed a high acid tolerance which could grow at ume-vinegar solutio n (contained of 1.58% citric acid, 0.76% malic acid and 7.97% NaCl) ad justed at pH 2.0. And, strains which were resist to low pH had a high ability of assimilation of organic acid and induced rise of the pH of ume-vinegar. In conclusion, it was suggested that these strains which had a high ability of assimilation of organic acid in ume-vinegar solu tion were main yeast contaminant in salted ume-processed products.