Viscoelastic Properties of Oil-Water Interfaces Covered by Bovine ß-Casein Tryptic Peptides

¹ Laboratoire des BioSciences de l'Aliment, Unité associée à I'INRA, Université Henri Poincaré-Nancy 1, B.P. 239, 54506 Vanduvre-lès-Nancy, France
² Laboratoire d'Ingénierie Moléculaire et Sensorielle de l'Aliment, ENSBANA, 1 Esplanade Erasme, 21000 Dijon, France

A combination of proteolysis and dilational rheology has been used to study the behavior of films of ß-casein (ß-CN) and of peptides spread at the oil-water interface. Identification of the peptides produced by trypsin hydrolysis of ß-CN in emulsion at 37°C provided information on the structure of ß-CN adsorbed at the oil-water interface. Good interface properties were observed for ß-CN or its peptides, probably because of the amphipathic nature of ß-CN or a synergistic effect between hydrophilic and hydrophobic peptides. Remarkable surface activity was found for the amphipathic peptide ß-CN (f114-169). Rheological studies had shown that interface films made with peptide fractions or with ß-CN were elastic rather than viscous. Film made with the purified peptide ß-CN (f114-169) was merely elastic at the triolein-water interface. A decrease of the viscoelastic modulus was observed for aging ß-CN film but not for aging peptide films; The ß-CN decrease was related to the flexibility of its structure. When the interface is increased by the dilation of an aqueous droplet plunged into oil, ß-CN may expose new polypeptide trains to cover the increased interface, unlike peptides with simpler structures.

Key Words: oil-in-water emulsion • casein hydrolysis • bovine milk • viscoelasticity

Submitted on December 1, 1999
Accepted on May 15, 2000