Super-Concentrated Incubation And Biological Changes Of Streptoccus Thermophilus

In order to develop a super-concentrated incubation method of Streptococcus thermophilus(S.t), the research was conducted to screen the main nutritive substances firstly on the basis of basic medium, and then to screen the multiplication factors (MFs), as a result,the ingredients of super-concentrated substratum were determined.The metabolic regularities of Streptococcus thermophilus on the nutritive substances of saccharine, protein and fat in the culture medium and the changes of ultra-structure and the apoptosis during super-concentrated incubation were studied by applying the method of centrifuge-semi-continuous process and by the super microscope, TUNEL staining and agarose gel electrophoresis (AGE), respectively, and the research provided the foundation for the super-concentrated incubation technique of Streptococcus thermophilus.In the paper, the enrichment culture formula of Streptococcus thermophilus and its cultural condition were determined. The culture medium contained the following ingredients: 1.5% lactose, 0.25% glucose, 1.5% soy peptone, 1.0% lactoalbumin hydrolysate, 1.5% yeast extract powder, 3.5% saline solution, 0.15% vitamin c, 0.1% lysine, 0.05% glutamate, 0.05% arginine, 5% malt wort and 5% tomato extract. The enrichment procedure was followed by semi-continuous approach, and the bacteria count could reach up to 1.032×l0¹⁰cfu/mL by the culture method of secondary centrifugation, about 10 times higher than the basal culture method, and it was proved to be a very effective super-concentrated incubation method for Streptococcus thermophilus.In conclusion, the lag phase of Streptococcus thermophilus was shorten in the eutrophy culture medium, and the time achieving the culminated point of logarithmic phase was shorted also, at the same time, the stationary phase lengthened. After secondary culture, Streptococcus thermophilus reached directly the log phase hardly through the lag phase, and then quickly reached the decline phase. There were more relations of the metabolic regalities of the three kinds of nutritive substances with the super-concentrated incubation process of Streptococcus thermophilus: the more the number of the bacteria, the quicker the metaboling, while the fewer, the slower the metabolism. Moreover, there apparently existed morphologic changes in this course, and there maybe existed the apoptosis, which correlated with bacteria propagation and acid producing. With the culture time postponed, the nutritive substances in the culture medium lacked also, and the morphologic change and apoptosis appeared more obviously.