Physicochemical behaviour of WPI-stabilized emulsions in in vitro gastric and intestinal conditions

Most studies on the in vitro lipid digestion of protein-stabilized emulsions have been carried out under simulated gastric and intestinal conditions. In this study, the digestion behaviour of whey protein isolate (WPI)-stabilized emulsions was examined under simulated intestinal fluid (SIF) conditions (pH 7.5, 2.5mg bile salts/mL and 0.8 mg pancreatin/mL) after the emulsions had been digested in a model simulated gastric fluid (SGF) containing pepsin (pH 1.6 and 3.2mg pepsin/mL) for different times. The droplet size, ζ-potential, microstructure, surface protein and amount of free fatty acids released were examined. The results indicated that WPI emulsions did not undergo pronounced changes in droplet size and microstructure during SGF digestion followed by coalescence during the subsequent SIF digestion. When WPI emulsions were treated with SGF, α-lactalbumin and a portion of β-lactoglobulin proteins adsorbed at the interface were hydrolysed by pepsin, resulting in small peptides being produced as characterized by sodium dodecyl sulphate polyacrylamide gel electrophoresis. In general, digestion in SGF containing pepsin accelerated coalescence of the emulsion droplets during subsequent digestion in SIF containing pancreatic lipase. However, the changes in the size, the microstructure and the proteolysis of the interfacial proteins of the emulsions under gastric conditions did not influence the rate and the extent of lipid digestion in the subsequent intestinal environment.