Study On High Activity Lyophilized Starter Culture Of Yoghurt

Since freeze-dried starter culture of yoghurt came to market for over twenty years, similar high performance starter culture had not yet been able to manufacture in china. At this situation, most of domestic dairy factory had to depend on importing freeze-dried starter culture of yoghurt, which markedly prevented the progress of dairy in china. The aim to the paper was that exploring the new technology for producing high activity lyophilized starter culture of yoghurt, finding out the key factor that leading the loss of activity of starter culture.During compare the milk with non-milk medium as culture medium, it was found that milk was superior to non-milk as culture medium of freeze-dried starter culture, and the coagulating time of lyophilized starter culture made of milk medium was 55 min less than that made of MRS.The number of bacteria couldn't decide the performance of freeze-dried starter culture during cultured. 42℃ was chose as the optimum cultured temperature when freeze-dried starter culture was manufactured. Although bacteria, even 2 times more, could be harvested in 30℃ than 42℃, the activity of freeze-dried starter culture made up of the bacteria was very low, and their coagulating time was 50min more than 42℃.The method, continuous adding alkali during culturing of bacteria, not only could get 3.6 times more bacteria than common one, but also increase activity of lyophilized starter culture, and its coagulation time could be shorten for 35min.Preincubation could help bacteria recovery from inactive state when freeze-dried to active state when rich cultured, and the optimum temperature of preincubation is 42℃ and time is 60min to selected strains in the paper. The coagulation time of lyophilized starter culture made by preincubation is shortened 25min than the control.The survival of bacteria of freeze-dried starter culture of yoghurt was 70% over after experiencing freeze-drying, when the time of pre-freezing was less than 24 hours, and time to 192 hours, the survival of bacteria markedly decline, only 48%.