The Preparation Of Freezing Drying Lactobacillus Starter And Its Physiological Activity In Preservation Process

Lactic acid bacteria is a kind of Gram-positive bacteria which is able to metabolize carbohydrates into lactic acid. And the freezing drying lactobacillus starter refers to one kind of starter made by the technology of freeze-drying,which can be used directly in the production of yogurt because of its high fermentation ability The product quality is stable, so it is widely used in food process as functional food products. With the rapidly development of fermented dairy product industry, it will be very important to study the high activity concentrated yoghurt starter culture for promoting the industrial process of lactic acid bacteria starter and development of fermented dairy industry. The purpose of the present study was to shorten the gap between China and developed countries in the production and preservation of lactic acid bacteria starter, and at the same time cut the cost of production.In this paper, we studied the isolation and purification of the lactic acid bacteria strains, the group growth behavior of the Lactobacillus, the condition of optimization of mixed culture of Lactobacillus and Streptococcus, and the activity during the preparation and preservation of the freezing drying lactic acid bacteria starter. The main results were shown as following:Lactobacillus and Streptococcus isolated from yogurt purchased from local market were identified as Lactobacillus delbrueckii subsp. lactis and Streptococcus thermophilus basing on morphological observation and16SrRNA sequence.By virtue of spline interpolation method and numerical differential method, a new method has been developed to distinguish the growth process into four different continuous phases:the accelerating growth phase, the constant growth phase, the decelerating growth phase and the declining phase. Basing on this, we studied the influence of different inoculum physiological condition, the inoculum size, and the types of carbon source on the growth behavior of Lactobacillus.The results showed that the largest biomass was gotten when we used the cell in the accelerating growth phase as the inoculum, and the time needed to get the1/2maximum biomass is the shortest. Even the initial concentrations of culture are different, the maximum biomass is similar, but when the concentration is106cfu/ml, the time needed to obtain the1/2maximum biomass is the shortest. Furthermore, the optimal carbon source for Lactobacillus is glucose.Through the single factor experiment, PB test, CCD experiment and the response surface analysis test, the influence of7factors on the mixed culture of Lactobacillus and Streptococcus was studied and the results showed that this method can not decide which factors play the key roles.In the last study we used the methods of flow cytometry, MTT dehydrogenase activity and plate count technique to test the ability of the starter. The results showed that, in-80℃freezing process, the number of living cells has no big change in order of magnitude when the CFU method was used, while in the process,of vacuum drying it decreased by two orders of magnitude. In4℃preservation process, the livability test by flow cytometry is47.22%, and the result test by CFU method is14.89%, then the MTT dehydrogenase activity is stabilize.