Effect of Ultra-High-Temperature Steam Injection on Model Systems of α-Lactalbumin and β-Lactoglobulin

Model systems of proteins of milk serum were heated to 143 + 1 C by steam injection, held for 8 to 10 s and vacuum cooled, c~-Lactalbumin was more resistant to heat denaturation when processed alone than when mixed with 134actoglobulin according to electrophoretic and densitometric quantification. Variants A and B of t3-1actoglobulin were sensitive to ultra-high-temperature processing. A new component with mobility intermediate between ~-lactalbumin and /3qactoglobulin formed after ultra-high-temperature processing. Analysis of the new component indicated that it was a protein complex of a-lactalbumin and fl-lactoglobulin. 13-Lactoglobulin was the major source of available sulfhydryls. The experimental sulfhydryl value for a mixture of alactalbumin and /3-1actoglobulin was 17% lower than calculated from the composition of the mixture. This was possibly because sulfhydryl groups are involved in the heat-induced complex. serum proteins (6).