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INVESTIGATION OF THE PROCESS OF EXOPOLYSACCHARIDES SYNTHESIS BY LACTO- AND BIFIDOBACTERIA CONSORTIUM IN THE DAIRY ENVIRONMENT
Abstract
When fermenting dairy environments under conditions other than optimum, due to the formation of an exopolysaccharide capsule in lactic acid bacteria, resistance to aggressive external factors, such as acidity, temperature, and ultrasound, increases. The synthesis of exopolysaccharides contributes to the intensification of milk fermentation and an increase in the proportion of physically and chemically bound moisture. The purpose of the experiment was to study the activity of polysaccharide biosynthesis by a consortium of probiotic microorganisms (Str thermophilus, L. casei subsp. Rhamnosus, L. acidophilus, L. plantarum, L. fermentum, B. bifidum, B. longum, B. adolescentis) in the process of thermostating at 4-6 °C. The accumulation of polysaccharides in the system was investigated by changes in the content and ratio of various forms of bound moisture based on the control of the mass change of the test sample when heated in the temperature range of phase transformations of moisture in samples 303-573 K, at a heating rate of 5 K/min. Experimental thermogravimetric data allow a quantitative assessment of moisture fractions with various forms of bonds. The metabolism of the probiotic microorganism under study at 277-279 °C is confirmed by a decrease in pH from 4.63 to 4.50. The characteristics of the thermal effects of thermolysis of test samples thermostated at these temperatures for 1, 14, 24 days showed a decrease in enthalpy from 2.194 to 1.86 J/kg, an increase in the temperature of complete dehydration of the sample from 129 to 144 °C, and a reduction in the change in mass of the sample from 91.72 to 84.39%. As a result of heat exposure, the weight of the samples under study changed and amounted to 0 days - 5.12%, 14 days - 7.75%, 24 days - 11.88%. Heating of samples and removal of free moisture in cells of casein-polysaccharide gels occurs in the temperature range of 295-303 K. At a temperature of 303-349K, water-water bonds are destroyed, the amount of moisture removed is 14.72%, 12.25 %, 11.37% in samples stored 0, 14 and 24 days, respectively. In the temperature range of 334-386 K, the corresponding removal of mechanically bound (adsorption) moisture,the mass fraction of moisture removed was 65.76%, 63.91%, 60.25% for the studiedsamples stored 0, 14 and 24 days, respectively. Analysis of the amounts of moistureremoved in the temperature range of 371-417 K indicates an increase in the massfraction of physico-chemically bound moisture for samples stored for 14 and 24 days. Comparison of the characteristics of these temperature ranges allows to state an increase in the proportion of chemically and mechanically bound moisture in the test samples during storage compared with the initial values, which confirms the presence of exopolysaccharides synthesis of probiotic microorganisms consortiums studied at a temperature of 4-6 °C.
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