Freezing effect on bacterial concentrate proteolytic activity

The purpose of research is to study the effect of freezing conditions on the proteolytic activity of symbiotic starter. Freezing was carried out in a refrigerator LGPv 8420, Liebherr. Solutions of glycerol, gelatin, and sucrose were used as cryoprotectants, with which the concentrated bacterial mass was suspended. As a result of the research of thermal analysis data, a thermogram of the process of freezing a symbiotic starter was obtained. A cryoscopic temperature of minus 2.8 °C, an optimal freezing temperature of minus 25 °C, and a process duration of 90 minutes were established. Further studies were carried out on the proteolytic activity of thawed samples on milk agar. The study of the effect of various cryoprotectants on the preservation of the proteolytic activity of the bacterial concentrate indicates that the use of glycerol as a protective medium has a positive effect on its functional properties. The proteolytic activity of the microflora affects the formation of the amino acid composition of the product. The paper analyzes the amino acid composition of the product obtained by fermenting milk with a thawed bacterial concentrate. For control, kurunga was used on liquid kurunga sourdough on skimmed milk. Amino acid analysis of the samples was carried out by ion chromatography with post-column derivatization of amino acids with ninhydrin in the acid hydrolyzate of the sample on an INGOSААА-400 amino acid analyzer. The level of balance of the amino acid composition of milk fermented with thawed bacterial concentrate with glycerin was determined. The data obtained made it possible to establish that freezing at minus 25 °C for 90 minutes with glycerin allows maintaining the high proteolytic activity of the microbial consortium and obtaining a dairy product with a complete protein composition.