Abstract: Four different cell wall disruption methods, such as ultrasonic treatment, lysozyme digestion, repeated freezing and thawing and mechanical disruption were respectively used to treat Streptococcus thermophilus SP1.1 cells, and the resultant cell wall disruption rates and the activities of the intracellular enzymes β-galactosidase and lactate dehydrogenase in centrifuge supernatant obtained after cell wall disruption were compared with the aim of screening the most appropriate method for cell wall disruption of Streptococcus thermophilus SP1.1. These four methods exhibited a large difference in their effectiveness, and lysozyme digestion provided optimal extraction of β-galactosidase (0.387 U) and lactate dehydrogenase (2.375 U), yielded a cell wall disruption rate of 99.87%, and was significantly different from three others (P <0.01). The optimum cell wall disruption conditions for 8 mL of 1.3 × 109 CFU/mL cell suspension by lysozyme (20000 U/mL) digestion were temperature of 37 ℃ and treatment time of 30 min and enzyme loading of 1 mL. A cell wall disruption of 99.99%, a β-galactosidase activity of 0.429 U and a lactate dehydrogenase activity of 2.431 U were obtained under these conditions.

Key words: cell wall disruption method, Streptococcus thermophilus, intracellular enzyme