Isolation of proteolytic psychrotrophic yeasts from fresh raw seafoods

A total of 103 cultures of yeasts were isolated from seven kinds of fresh raw seafoods. The isolates comprised six genera, Candida, Cryptococcus, Debaryomyces. Rhodotorula, Sterigmatomyces and Trichosporon, and included 21 different species. All the isolates were psychrotrophic yeasts. Proteolytic activities of 50 psychrotrophic strains were studied by use of skim milk within the temperature range of 0-42-degrees-C. All the strains showed various degrees of proteolysis. In particular, Candida lipolytica, Trichosporon pullulans and Candida scottii were active species at low temperatures. Sensory spoilage due to the proteolytic yeasts were observed in mackerel homogenates stored at 10-degrees-C. C. lipolytica-inoculated homogenates caused spoilage with ammoniacal odours after 1 week of storage. Values of total volatile basic nitrogen at 10-degrees-C were highest with C. lipolytica among 35 strains tested, followed by Tr. pullans, Trichosporon cutaneum, C. scottii, Rhodotorula glutinis and Cryptococcus luteolus. Proteolytic psychrotrophic yeasts were widely distributed in raw seafoods.