β -Galactosidase activity of bacteria as a criterion of selection of strains for the composition of starter cultures

β-galactosidase activity is one of the criteria of the selection of strains for the composition of bacterial preparations for sour-milk products of special purpose. This enzyme is key in the cleavage of milk lactose by starter microorganisms. One of the important criteria for the formulation of starter compositions in the production of fermented milk products is their composition. The main stages of the selection of lactobacillus, bifidobacterium and propionic acid bacteria and the creation of their compositions with high β-galactosidase activity for the production of fermented dairy products are presented in this paper. It is found that strains of thermophilic streptococci in their development in the milk lead to the greatest reduction of lactose, this indicating of their high ability of producing β-galactosidase activity as compared to Bifidobacterium ssp, and Propionibacterium freudenreichii ssp. schermanii. The highest β-galactosidase activity manifests symbiosis microorganisms Streptococcus thermophilus, bifidobacteria and propionic acid bacteria, namely – 604 A/min. The quality and biological value of sour-milk products directly depend on the starter preparations used. Therefore, in order to obtain fermented milk products of special purpose with low lactose concentration, high-activity strains of microorganisms were studied. The utilization of lactose in the finished product, in the strains studied and their combinations studied varies widely from 12,1 % to 35,8 % of its initial concentration. It is shown that β-galactosidase activity and utilization of lactose in the finished product are strain-specific features. As a result of studies carried out, the use of Streptococcus thermophilus, Bifidobacterium bifidum, B. longum B. adolescentis and Propionibacterium freudenreichii ssp. schermanii strains, formulating new starter culture, is recommended for sour-milk prodacts of special purpose