Cryoprotectors selection to freeze bacterial concentrate of symbiotic starter

The aim of the reseach is to study the effect of cryprotectors of various compositions on the preservation of the microflora of the bacterial concentrate of the symbiotic starter culture in the course of freezing. Research objectives are: selection of the type and dose of cryoprotectant for freezing the symbiotic bacterial concentrate; assessment of the level of survival of viable cells; study of the enzymatic activity of frozen bacterial concentrate. The bacterial concentrate microflora is identical to the natural ferment for the production of kurunga. The object of the research was the cryprotectors glycerin, sucrose, gelatin - substances that prevent water crystallization; bacterial concentrate of symbiotic kurung starter culture. A nutrient medium with buffer salts was used as a base mixture. Standard and generally accepted research methods were used. Titratable acidity was according to GOST 3624 by titration with 0.1 n. sodium hydroxide solution with phenolphthalein. The value of active acidity was according to GOST P 53359-2009 by potentiometric method on an Anion-7000 device. The effect of cryoprotectants on the preservation of the viability of microorganisms of the bacterial concentrate of the symbiotic starter culture was examined by freezing in a freezer to -25 °C at a cooling rate of 100 °C per minute. The effectiveness of cryoprotectants was assessed by the number of viable cells of the main groups of microorganisms in the starter culture and the enzymatic activity of the thawed bacterial concentrate. The results obtained showed that the use of 5 % glycerol and gelatin over 5% in the composition of the protective medium retains the original properties of the bacterial concentrate and promotes the survival of yeast cells. The use of sucrose ensures the preservation of only lactobacilli. The study of the enzymatic activity reveals that the bacterial concentrate, frozen in a protective environment with 5 % glycerin, ferments milk within 10-12 hours. The high level of restoration of the starter culture activity is associated with the endo- and extracellular properties of glycerin.