Yeast Contamination of Chilled Salad and Gyoza from Retail Markets

Abstract

Microbiological examination of chilled potato and macaroni salad (20 samples) and Chinese dumplings (“Gyoza”) (19 samples) was carried out to examine the microflora, especially the yeasts, of these market foods. The samples were corrected from retail markets by official food examiners and investigated by the official microbiological methods. Counts of bacteria, yeasts and fungi in the salad samples were found to range from 10³ to 10⁵, 10¹ to 10⁵, and below 10³ per gram, respectively. In general, the counts of the Gyoza samples were lower than those of the salad samples.
In the samples of salad, yeasts were found to be the second largest microbial group, and the predominant species were Candida (C. intermedia, C. lipolytica, C. parapsilosis, C. sake, etc.), Rhodotorula (R. glutinis, R. minuta, R. rubra), Trichosporon (Tr. cutaneum, Tr. pullulans) and Cryptococcus (Cr. albidus, Cr. infirmo-miniatus, Cr. laurentii). Yeast flora in the samples of Gyoza included Candida, Rhodotorula, Debaryomyces, etc. In the two kinds of samples tested, the main bacterial genera were Pseudomonas, Klebsiella, Lactobacillus, Bacillus, Staphylococcus, etc., and representative fungal genera were Penicillium, Phoma, Cladosporium, etc.
Psychrotrophic organisms grown within 2 weeks at 5°C accounted for 92.9% of the total yeast cultures and 47.1% of the total fungal cultures isolated from all the samples tested. The obligately psychrotrophic yeasts from the chilled salad were Cr. infirmo-miniatus and Trichosporon spp.