Cryopreservation to be a progressive method for keeping up valuable strains of lactic acid bacteria and yeasts

In fodder production, lactic acid bacteria are used in silage making to improve fodder storage and quality due to suppressing undesirable butyric acid bacteria, enterobacteria and the yeasts, which cause fodder contamination with butyric acid and aerobic spoilage (a role of lactic acid bacteria in haymaking is criticized). In bakery, the lactic acid bacteria and yeast compositions are used as starter cultures to control the proper fermentation in rye and wheat sourdough. To provide industry with pure cultures of microorganisms, it is necessary to keep up their active samples in collections and to control the biotechnological properties. The paper presents experimental data on the viability and biotechnological properties of industrial strains of lactic acid bacteria and yeasts from the collection of the Saint-Petersburg Branch of the State Research Institute of the Bakery Industry during cryopreservation at -80 °С according to different protocols. Studies have shown that the viability of ten Lactobacillus strains depended on the initial concentration of cells and the presence of cryoprotectants. Simultaneous use of 30 % glycerol and 17 % sucrose in a protective medium, as well as an increasing titer by centrifugation to 10 7-10 8 cells/ml led to a slight drop in the viability and acidifying activity of lactic acid bacteria after two years of storage (less than 20 and 16 %, respectively). It was shown that the result of cryopreservation of yeast depends on the presence of cryoprotectant and age of the culture. To the end of storage, survival and fermentative activity of the strain Saccharomyces cerevisiae, frozen in a stationary growth phase using 15 % glycerol, were 99.8 and 77.9 %, respectively. The strain Candida milleri was less stable and its viability dropped more than 30 %. The results obtained can be used to develop the guidelines for a cryopreservation of lactic acid bacteria and yeasts that are used in the sourdough bread production, and also in agriculture, particularly in fodder production.