Isolation, Identification and Control of Osmophilic Spoilage Yeasts in Sweetened Condensed Milk

In this paper, six yeast strains were isolated from spoilt condensed milk in the agar culture media with high sugar content. By employing API 20C AUX strip, these six isolates were identified as Candida pelliculosa strains. Their growth characteristics were then examined under different culture conditions, including various pH value, temperature, sterilization condition, NaCl and glucose concentrations. Both culture temperature and pH value showed significant influence on the growth of the strains, with the optimum cultural temperature and pH being 33°C and 5.0, respectively. The biomass was evidently depressed by increasing the concentrations of salt and glucose. However, it was also found that the strains tested were able to tolerate high concentrations of NaCl (9-15%) and glucose (60-80%), suggesting that the strains isolated were of osmophilic yeast. To find efficient strategies for controlling the spoilage of condensed milk, a comparative study of the effects of eight antiseptics and heat treatment on these spoilage yeasts were done. Among the tested antiseptics, 0.01% sodium dehydroacetate or 0.03% ethyl p-hydroxybenzoate showed application potential in inhibiting yeasts-caused spoilage of sweetened condensed milk.   Key words: Sweetened condensed milk, spoilage yeast, isolation and identification, control