Isolation And Control Of Osmotolerant And Spoilage Yeast

The osmotic pressure of condensed milk, soy sauce and syrup, the familiar food in our daily life, is high. In normal conditions, the sterilization methods of controlling microorganisms of these food is pasteurisation combined the high osmotic pressure. But the nonstandard operational approach and insanitary conditions in the plants may lead to the pollution of the microorganisms. And once the microorganisms can grow in the high osmotic pressure conditions, the food will corrupt. The corruption of the condensed milk, soy sauce and syrup happened from time to time. It brought serious loss to the producers and may threaten the health of the consumers. So it is necessary and useful to study the characters of the Osmotolerant and Spoilage Yeast and control their growth.In this paper, the microbial change was tested between the normal and spoilage food(condensed milk, soy sauce and syrup). The results of Aerobic plate count in the normal and spoilage food both can meet the sanitation standard. But some microorganisms are isolated from the spoilage food and none from the normal food in the high-concentration sugar culture medium. And they all can cause the spoilage of aimed normal food. Spoilage features of these kinds of microorganisms were observed and API 20C AUX strip were used to identify the spoilage microorganisms. The results showed that L1, L2, L3, L4, L5, L6 and J1, J2, J3, J4, J5, J6 and M1, M2, M3, M4, M5, M6 were respective the same microorganisms. It were found that L1, L2, L3, L4, L5, L6 were Candida pelliculosa, J1, J2, J3, J4, J5, J6 were Candida lambica, M1, M2, M3, M4, M5, M6 were Geotrichum candidum.The growth characteristics under different conditions of L1, J4 and M5 were studied in this paper. By analysis of the different pH value, NaCl concentration, glucose concentration, and the sterilization condition, it was found that the pH value and the sterilization factors could effect the growth of them and they grew well around pH 5.0-6.0 and could resist high osmotic pressure. But they didn't resist the high temperature, they can be sterilized at 60℃, 20min or 70℃, 5min.Inhibition experiments and inhibition filtration to the spoilage yeasts were done. Several gradient concentration of inhibition solution were selected to confirm the approximate action range of the antimicrobial agent, then the minimum concentration of final inhibitory concentration were determined. The results showed that sodium benzoate, potassium sorbate, ethyl p-hydroxybenzoate, sodium dehydroacetate and natamycin had significant inhibition. And the MIC (minimum inhibition concentration) of ethyl p-hydroxybenzoate and sodium dehydroacetate to L1 were 0.03% and 0.01%; the MIC of sodium benzoate and sodium dehydroacetate to J4 were 0.02% and 0.01%; the MIC of sodium benzoate and potassium sorbate to M5 were 0.04% and 0.03%. The MIC results would be directly applied to respective foods. And it was found that the inhibitors at minimum inhibition concentration can control the reproduction of the spoilage yeast and prevent food spoilage.