Abstract
The article presents the results of a study aimed at a comparative analysis of postbiotic isolation methods and determining the yield and antioxidant activity of preparations obtained from Lacticaseibacillus sp., Leuconostoc sp., and Saccharomyces sp. strains isolated from traditional fermented products (shubat, sauerkraut, and kumiss). Based on an analysis of literary sources, three methods were selected for experimental studies: thermal cell inactivation, ethanol precipitation, and ultrafiltration, characterized by technological simplicity, cost-effectiveness, and the ability to preserve biologically active components. The yield of postbiotics was determined gravimetrically, antioxidant activity by DPPH and ABTS tests, and microbiological safety by the absence of viable cell growth. It was found that the thermal method provides the highest dry matter yield (90-92%), high antioxidant activity (86-89%), and complete microbiological safety compared to other methods. A gentle inactivation regime (70°C for 30 min) preserved functional metabolites without destroying low-molecular-weight antioxidants and exopolysaccharides involved in redox processes. The highest activity values were obtained for the Leuconostoc sp. strain, which is due to the presence of an exopolysaccharide matrix stabilizing the active compounds. The obtained results confirm the feasibility of thermal inactivation as an effective and affordable method for isolating postbiotics for the development of functional dairy products and the expansion of biotechnological approaches in the food industry.