Evaluation of the proteolytic activity of new cryoresistant lactobacillus strains

The search for new functionally active strains of lactic acid bacteria, together with the development of domestic competitive starter cultures on their basis, are important directions of contemporary food biotechnology. Proteolytic activity represents one of the criteria for selecting lactic acid bacteria strains for their subsequent use in food production and largely determines the quality characteristics of the finished product. The present study aims to evaluate the proteolytic activity of 15 new cryoresistant strains of Lactobacillus genus lactic acid bacteria having a number of functional and technological properties. According to the results obtained, all strains demonstrated higher proteolytic activity in alkaline media and those close to neutral (pH = 6.5). In slightly acidic media, the strains under study showed minimal values of proteolytic activity, except for L. fermentum 12 and L. plantarum 21 strains. Strains L. casei 32, L. casei 36, L. fermentum 10, and L. acidophilum 9 (48.9–52.3 µg tyrosine/mL·min) showed the maximum proteolytic activity. The minimal proteolytic activity was characteristic of L. fermentum 12, L. fermentum 24, and L. plantarum 1 (27.7–28.9 µg tyrosine/mL·min). The studied paramenter depends on the conditions of proteolysis (substrate, medium pH) and represents an individual strain characteristic independent of the lactobacillus species membership. According to the results obtained, L. casei 32, L. casei 36, and L. fermentum 10 cryoresistant strains, manifesting high proteolytic activity and effectively affecting various protein substrates (casein, albumin, haemoglobin) in a wide range of medium pH values, can be recommended for inclusion in the composition of starter cultures for the production of fermented food products.