Dynamic surface properties of the proteose-peptone fraction of bovine milk

Proteose-peptone is a heat-stable and acid-soluble protein fraction of milk that has important functional properties. Component 3, which is the most hydrophobic fraction, appears to be largely responsible for the physicochemical properties of proteose-peptones and for their important biological role in milk. In this study, total proteose-peptone was prepared from bulk skim milk by precipitation with ammonium sulfate, and the hydrophobic fraction was purified by FPLC(R) (Pharmacia Fine Chemicals, Uppsala, Sweden). The drop volume method was used to investigate the dynamic surface activity of total proteose-peptone and component 3 of proteose-peptone at the air-water interface and at the oil-water interface. In general, proteose-peptones are good surfactants at both interfaces. Of all proteose-peptones, component 3 causes a more rapid reduction of interfacial tension in both interfaces. A system for measuring film balance was used to obtain more information about the surface and mechanical properties of proteose-peptone monolayers. We deduced from the compression isotherms that component 3 of proteose-peptone and total proteose-peptone films spread at the air-water interface present different mechanical properties.