Abstract
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
Highlights
Yeasts, one of the most important microorganisms in food industry, have been widely used in the production of bread, beer, wine and other alcoholic drinks for thousands of years
To isolate the spoilage microorganisms, the microbes from different samples of sweetened condensed milk, including spoiled samples with little gas (Group 1), spoiled samples filled with gas (Group 2) and normal samples (Group 3), were cultured with three kinds of media
The results indicated that the use of 0.01% sodium dehydroacetate or 0.03% ethyl p-hydroxybenzoate could be a useful method to inhibit the growth of spoilage yeasts and extend the storage time of sweetened condensed milk
Summary
One of the most important microorganisms in food industry, have been widely used in the production of bread, beer, wine and other alcoholic drinks for thousands of years. They have found applications in many products such as ethanol for fuel, yeast extracts, pigments, probiotics and other specific substances for foods and feeds, as well as biochemicals for the pharmaceutical industry. Except for their well-known fermentation capabilities, they are responsible for the spoilage of certain foods and beverages (Jakobsen and Narvhus, 1996). In 1980s, Fleet firstly reported that yeasts were suspected of being associated with a food-borne gastroenteritis incident (Fleet, 1992)
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