Proteomic profiling of the coagulation of milk proteins induced by glucono-delta-lactone

Abstract

This study investigated the glucono-delta-lactone (GDL)-induced coagulation of milk proteins at 30 °C. The addition of 0.5 M GDL caused milk proteins to coagulate following a 1 h incubation period. Approximately 90.7% of milk proteins were coagulated into the milk pellet fraction (MPF), and the protein concentration of the milk supernatant fraction (MSF) decreased from 29.2 ± 1.1 mg mL−1 (control) to 2.7 ± 1.1 mg mL−1. The SDS-PAGE analysis demonstrated that the protein bands corresponding to αS-casein, β-casein and κ-casein in the MSF decreased to 0.2 ± 0.1, 0.5 ± 0.2 and 0.5 ± 0.3% of their original levels, respectively. However, only 29.5% of the β-lactoglobulin was coagulated into the MPF following the treatment with 0.5 M GDL. Two-dimensional electrophoresis analysis indicated that isomers of αS1-casein, αS2-casein, β-casein and κ-casein, as well as a fraction of β-lactoglobulin and α-lactalbumin, were coagulated from the MSF into the MPF following incubation with 0.5 M GDL.