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In order to know the influences of heat treatment of yoghurt on pH, β-galactosidase and viable cells, yoghurt sample was made by general method with Lactobacillus bulgaricus and Streptococcus thermophilus, and the changes in pH, β-galactosidase-activity and viable cell-count were determined during heating at 55℃ and 70℃. The pH of yoghurt was not changed when the yoghurt was heated at 70℃, but at 55℃ it decreased slightly. The stability of β-galactosidase was not affected markedly by heat treatment at 55℃, but was rapidly inactivated at 70℃. The heat treatment of yoghurt at 55℃ had the halb of viable cell in 1 hour, but the heat treatment at 70℃ had considerable effect on viable cell in 5 minutes.
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