Yeast Contamination of Chilled Raw Seafoods

Abstract

Microbiological examination of chilled roe of sea urchin (Namauni; Heriocidaris spp., etc., 20 samples), sliced raw tuna (Maguro sashimi; Thunnus spp., etc., 20 samples) and the foot of the hen clam (Bakagai sashimi; Mactra spp., 17 samples) was carried out to examine the microflora, especially the yeasts. The samples were collected from retail markets by official food examiners and investigated by the official microbiological methods. Counts of bacteria, yeasts and fungi in the samples of roe of sea urchin ranged from 10³ to 10⁷, 10² to 10⁷ and below 10⁴ per gram, respectively. Counts of bacteria, yeasts and fungi in the samples of sliced raw tuna and the foot of the hen clam were found to range from 10³ to 10⁶, 10¹ to 10⁴ and 10⁴ per gram, respectively.
In the three kinds of seafood samples, yeasts were found to be the second largest microbial group and the predominant species were asporogenous yeasts such as Rhodotorula (R. glutinis, R. rubra, R. pallida), Candida (C. guilliermondii, C. humicola, C. lipolytica, C. parapsilosis, C. zeylanoides), Trichosporon (Tr. cutaneum, Tr. pullulans, Tr. variabile) and Cryptococcus (Cr. albidus, Cr. infirmo-miniatus, Cr. laurentii, Cr. macerans). Trichosporon cutaneum, a species of opportunistic pathogen, was isolated from 45% of the samples of sliced raw tuna. In all the samples tested, the main bacterial genera were Pseudomonas, Corynebacterium, Micrococcus, Staphylococcus, etc., and representative fungal genera were Penicillium, Phoma, Fusarium, Mucor, etc.
Psychrotrophic organisms grown within 2 weeks at 5°C accounted for 94.6% of the total yeast cultures and 55.0% of the total fungal cultures isolated from the seafood samples.