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Three strains of inhibitory lactic acid bacteria (No. 49, No. 61, No. 75) against Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escheirchia coli(ATCC33694) and Bacillus subtilis(ATCC6633) were isolated from kimchi, and then, identified to be Lactobacillus plantarum after examinations of their biological and physiological characteristics. To investigate a possible application of these three lactobacilli in milk fermentation industry, we made yogurts and then evaluated their β-galactosidase activities at various; incubation time(from 24 hrs to 72 hrs). The result of experiment was that β-galactosidase activities were reached maximum at 48 hrs and that reduced gradually with the lapse of time. And the β-galactosidase activity of lactobacilli, and their viable cell counts at 37℃ for 2 hrs under various pH conditions were investigated. β-galactosidase activities of 3 strains were reduced 50% at pH 3.5, but there were no remaining activities at pH 2.5, and pH 1.5, respectively. The frequency of the survival cell of lactobacilli in yogurt were 0.12∼0.75% at pH 2.5. 6.3×10^(-5)∼2.7×10^(-3)% at pH 1.5, respectively, but there was no significant difference at pH 3.5. The values of original pH, titratable acidity as lactic acid, viscosity, and viable cells of yogurts were 4.08∼4.30, 1.05∼1.25%, 1,818∼2,124 cps and 7.3×10^8∼3.0×10^9 cfu/㎖, respectively. To estimate buffer capacity of yogurt, the volume of 1.0 N HCl to 2 unit below original pH of yogurt(100 ㎖) was 11.98∼13.02 ㎖ and the volume of 1.0N NaOH to 4 unit above original pH of yogurt(100 ㎖) was 10.82∼12.86 ㎖.
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