Isolation of casein from buttermilk obtained during butter production by high-fat cream conversion

Buttermilk is a valuable secondary raw material produced in large quantities during the butter production. It contains all water-soluble components of milk (proteins, lactose, and minerals), as well as milk fat. Despite the existence of many well-known buttermilk-based products, such as fresh and fermented beverages, various types of cheeses – natural and processed, as well as condensed and dried products, the problem of its recycling has not been finally solved. Considering the compositional similarity of buttermilk to skim milk, particularly its high casein content, and its use for acid casein production may be promising. Therefore, the aim of our research was to determine the distribution of protein fractions during acid precipitation of casein from buttermilk obtained during the production of butter by high-fat cream conversion. Skim cow’s milk with an acidity of 18 °T and fresh buttermilk with a protein content of 3.0 % obtained from PJSC “Ternopil Dairy Factory” were used in this study. The casein content in the precipitate was determined by drying to constant weight at 105 °C, and the protein content in the casein whey was measured spectrophotometrically. The fraction composition of caseins precipitated from milk and buttermilk was analyzed using electrophoresis in homogeneous polyacrylamide gel in the presence of urea. Express electrophoresis under native conditions was used to study the protein fractions in the casein whey. As a result, it was established that the maximum yield of casein from buttermilk is achieved at a pH range from 4.5 to 4.7 and a temperature of 45–55 °C, and can constitute 2.65 ± 0.04 %. The casein precipitate contains some whey proteins. Accordingly, in the casein whey obtained during casein isolation from buttermilk, the content of the main whey protein fractions is significantly lower than in casein whey from skim milk, amounting to 34 ± 4 % for β-lg, 27 ± 3 % for α-la, and 37 ± 6 % for BSA. Immunoglobulins and proteose-peptone 3 are practically absent. The fractional composition of casein from buttermilk is similar to that of control acid casein from skim milk, except for a reduced content of κ-caseins.