Study of the physicochemical properties of buttermilk separation products with apple pectin

Experimental studies were carried out under the conditions of the Vologda Region. The objects of the study were: buttermilk, apple pectin concentrate, and buttermilk separation products: protein and aqueous phases. The purpose of the work was to study the physicochemical properties of the protein and water fractions separated during the fractionation of buttermilk with pectin. For this, an aqueous solution of apple pectin with a mass fraction of 6.5% was prepared. This solution was added to buttermilk in such an amount to obtain four variants of buttermilk mixture with pectin concentrations: 0.3%, 0.6%, 0.9%, and 1.2%. After holding for 10-12 hours at a temperature of 8-10 °C, each system separated into two phases. The upper phase was a transparent fluid solution of yellow-brown color, and the lower one was an opaque viscous system of white color. When studying the mass fraction of protein, it was found that the highest content in the protein fraction was achieved with a pectin content of 0.6%. When determining the active acidity, it was found that the pH range in both phases was in the interval from 6.8 to 7.2 units, which corresponds to a neutral and slightly acidic environment and is significantly higher than the isoelectric point of casein, equal to 4.6. The titratable acidity of the protein phase is higher compared to the original buttermilk and the aqueous phase, which is associated with the increased content of milk proteins and the concentration of pectin, which is also characterized by the manifestation of acidic properties. A significant decrease in the specific electrical conductivity of the protein phase compared to the aqueous one was established. This may be explained by an increase in the content of all components, including high molecular weight ones, in this phase, which limited the mobility of ions. The observed fractionation mechanism is assumed to be due to the interaction of the protein component with the pectin one. A pH value of 6.8-7.2 units indicates that the concentration and separation of the protein occurred without reaching an isoelectric state. Taken in totality, this indicates that the polysaccharide was precipitated along with the milk proteins.