Studies On β-galactosidase And Proteolytic Activities Of Lactobacillus Acidophilus And Lactobacillus Casei

The subject of present research is ?-galactosidase, proteolytic activities and some biological characteristics of them in yoghurt of six strains of Lactobacillus acidophilus and five strains of Lactobacillus casei.Strains were isolated from the koumiss samples collected from the heardsman,s house in Mongolia and Inner Mongolia – Xilingole District .The ?-galactosidase activities of Lactobacillus acidophilus and Lactobacillus casei were different. The activity range of ?-galactosidase was 0.767u~5.602u, and the average activity is 2.217u for the former. The range activity of ?-galactosidase was 0.211u~3.312u, and the average activity was 1.070u for the latter. Proteolytic activities varied among strains of L.acidophilus and L.casei .Temperature , pH , and reaction time affected the proteolytic activities. The maximal proteolytic activities of individual strains were different .With the increasing of the temperature the proteolytic activities of both strains were rising in this reseach. Some biological characteristics of the both cultures incubated in skimed milk at 37℃for 24 hours and then stored at 4 ℃for 21 days were studied . During the fermentation at 37℃ for 24 hours ,a significant increasing of acid production and soluble trysine in yoghurt were detected . At the end of fermentation , the average titration acidity of yoghurt inoculated L.acidophilus and L.casei were 115.5゜T and 99.36゜T respectively, correspondingly pH varied among 3.71~4.47 and 3.86~4.83 .The concentration range of soluble trysine was 95.70ug/ml ~ 135.15mg/ml for the former,and 94.80 ug/ml ~ 130.05 mg/ml for the latter. Some of ?-galactosidase and proteolytic activities of both strains were maintained during the observation stored at 4℃ for 21 days .L.acidophilus and L.casei both kept relatively high viability (>108cfu/ml) until the 21th day.