Evaluating the Proteolytic Activity of Lactobacilli in Cheese Production

As the range of domestic cheeses has increased, Russian cheese industry needs new monospecific starters with multidirectional or targeted actions. Advanced monospecific concentrates with strong proteolytic properties boost proteolysis, reduce ripening time, and improve the sensory profile of the finished product. This article describes some strains of mesophilic lactobacilli with good prospects for commercial cheese production. The lactobacilli strains were isolated from the collection of microorganisms of the All-Russian Scientific Research Institute of Butter and Cheese Production, Uglich, Russia. They included Lactiplantibacillus plantarum 28 and 37, Lacticaseibacillus casei 738-11, Lacticaseibacillus paracasei K-6, Lacticaseibacillus rhamnosus P, and Limosilactobacillus fermentum 39. The proteolytic profile was estimated by the amount of accumulated non-protein nitrogen and the buffer capacity of the water-soluble fraction. The skim-milk cultivation revealed two optimal strains with the highest proteolytic effect, i.e., L. rhamnosus P and L. paracasei K-6. They served as additional cultures to the main industrial starter. L. rhamnosus P accumulated biomass faster during processing and pressing; L. paracasei K-6 developed more intensively during ripening. The highest count of viable lactobacilli cells reached 8.55 lg CFU/g in the cheese samples with L. rhamnosus P and 8.94 lg CFU/g in the samples with L. paracasei K-6. L. rhamnosus P died slower and demonstrated a stimulating effect on lactococci. The high content of lactobacilli in the experimental cheeses (≥108 CFU/g) made it possible to classify them as dairy probiotics. The samples with L. paracasei K-6 and L. rhamnosus P proved to be more active proteolytics. By the end of ripening, the experimental samples contained 20% more non-protein nitrogen than the control. The cheeses fortified with L. paracasei K-6 received the highest score for taste and aroma, which correlated with the greatest change in the buffer capacity of the watersoluble fraction. L. paracasei K-6 and L. rhamnosus P in monospecific starters proved able to improve the quality of cheese and intensify its production.