CALORIMETRIC METHODS OF STUDYING STATUS INDICATORS OF VEGETABLE POWDERS BIOPOLYMERS
The conservation of water is considered to be the criterion for the conservation of the molecular composition of the desired beneficial substance in the plant powder. Active humidity and glass transition temperature reflect the content of water bound in these molecules. To assess the characteristics of plant powders, we established the dependence of their phase transition temperatures, rehydration properties on their particle size, molecular weight and active humidity. To achieve this goal, a calorimetric study was conducted. It was found that the freezing temperature of a wet powder with active humidity below 0,926 shifts below zero with temperature fluctuations and as a result of recrystallization. It is determined that the characteristics of the powders depend on their particle size. For plant powders with finer particles and low molecular weight, the glass transition and freezing temperatures are lower, rehydration is lower. It was determined that for plant powders with a glass transition temperature not higher than 153-170 °C, a temperature of 120 °C is the limiting heating temperature responsible for moisture binding during rehydration. To evaluate the relationship between free and bound water fractions and active humidity, a calorimetric method for the separate determination of water fractions has been developed. To evaluate the changes in the microstructure of vegetable powders during their heat treatment, which they will undergo, for example, when baking bakery products, enthalpy curves were obtained. On the thermograms, two endothermic peaks are observed: the first, in the range from 50 to 140 °C, reflecting the process of water evaporation; the second, at the level of 150 °С (for carrot and beet powders) and 172 °С (for pumpkin powder), which reflects the transition of the initial fibrous or crystalline structure to a plastic or molten state. This suggests that when baking bread, the powders of which are included in the recipe, their thermal decomposition will not occur, since the bread crumb warms up to a maximum of 96-98 °С, i.e. in the production of bakery products, the native physiological properties of the powders will be preserved.