| Two strains of lactic acid bacteria isolated from the koumiss were shown to inhibit the growth of Listeria monocytogenes .The culture medium ,the extraction of antibacterial substances and the application of antibacterial substances to pasteurized milk to retard the deterioration were studied. The optimum antibacterial activity of strain H1-1 was obtained under the culture of TPY adding 1% nitrogen source(trypticase:phytone peptone1:1), 3% glucose, 0.5% yeast, keeping pH value 6.5. The optimum antibacterial activity of strain H1-2 was obtained under the culture of TPY adding 1% nitrogen source (trypticase:phytone peptone3:1), 1% glucose , 0.5% yeast , keeping pH value 6.5. The antibacterial substances of strain H1-1 were composed of three kinds of proteins with molecule weight of 33,800Da,40,100Da and 42,800Da. The antibacterial substances of strain H1-2 were composed of two kinds of proteins with molecule weight of 22,700Da and 23,200Da. The results of the preserving function of different antibacterial substances concentration on pasteurized milk indicated the antibacterial substances inhibited the growth of bacteria in the pasteurized milk , retarded the pH declining speed and extended the market life.
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