Effect of the presence of montmorillonite on the solubility of whey protein isolate films in food model systems with different compositions and pH

Purpose of research: Whey protein isolate (WPI) coated plastics and laminates have potential for food packaging applications. Montmorillonite (MMT) addition to the WPI matrix for improved WPI material for such applications was investigated. The effect of the presence of MMT on the solubility of WPI films in food model systems with different compositions and pH, and on the morphology, mechanical properties, and swelling of the films was investigated. Results: The presence of MMT in the WPI films significantly reduced solids migration and altered the properties of the WPI films. The level of reduction was dependent on both pH and composition of the food model system. The lowest migration occurred in the acidic solutions due to a conformational change in the whey proteins and the resulting reduction of protein migration. This conformational change was pH dependent with lesser protein migration with lower pH due to electrostatic interactions between WPI and MMT. The swelling of the WPI film was reduced by 35% with a change in pH of the food model system from 6.5 to 2.85, regardless of the presence of MMT. Further lowering of the pH of the food model system led to a steady increase of swelling in the films but this effect was less pronounced in the case of MMT/WPI film due to electrostatic interactions between WPI and MMT. The presence of MMT also decreased the elongation at break and increased the tensile strength and surface roughness of the WPI film. Conclusions: The addition of MMT in the WPI matrix significantly reduces solubility and alters properties of the WPI films. The magnitude of change depends on the specific food characteristics including both, composition and pH. MMT and an external acidic stimulus can be used to improve the WPI film for food packaging applications. (C) 2014 Elsevier Ltd. All rights reserved.