Behavior of whey proteins-hidroxypropylmethylcellulose mixtures in gels and at the air-water interface.

PÉREZ, OSCAR E; WARGON, VICTORIA; RODRÍGUEZ-PATINO, JUAN M; PILOSOF, ANA MR.

Lussanne, Suiza

Congreso; Delivery Systems 2005; 2005

Nestle, Suiza

Hidroxypropylmethylcellulose (HPMC) is a water-soluble modified cellulose widely used in the food, pharmaceutical and cosmetic industries for its surfactant, thickening and gelling properties.It is also used in delivery systems for controlled release. HPMC solutions have the unusual property of  forming thermoreversible gels on heating. Use of mixed proteins and polysaccharides is gaining importance because of their synergistic interactions that offer the possibility for controlling or improving the structure and properties of colloidal systems. The phenomenon known as thermodynamic incompatibility generally occurs at pH higher than the protein isoelectric pH and/or at high ionic strengths in mixed solutions of protein + polysaccharide and is the main cause of synergistic effects. The aim of present work was to study the behavior and structure of whey proteins – hidroxypropyl methylcellulose gels and interfaces. Whey protein concentrate (WPC) and HPMC mixed systems were prepared by mixing  WPC and HPMC solutions of appropriate concentrations (pH = 7.0). The dynamics of gelation of single HPMC and WPC solutions and the mixed systems were determined by dynamic oscillation measurements  performed in a Phaar Physica controlled stress Rheometer (MCR 300). The gelation was also performed in test tubes at 90 °C and the structure analysed after cooling. DSC and optical microscopy were also used to understand the performance of the mixed systems. WPC-HPMC mixtures at room temperature were incompatible and rapidly separated into two phases. The volume of the separated phases and their protein/HPMC composition was determined after centrigugation. The gelation temperature of the mixed systems (WPC= 12-20% wt and HPMC= 1-3 % wt) mainly reflected the gelation of the protein phase. The  melting of gels was not observed. A great synergism between protein and HPMC was observed on elastic modulus. These gels after cooling showed an heterogeous structure in which the protein constituted the gelled phase and the polysaccharide the inner filler. Surface tension of adsorbed  films at the air-water interface and rheological properties were determined using an automatic drop tensiometer. A competitive behavior was observed in the mixed systems. HPMC was more surface-active than WPC and dominated the interface at short adsorption times. The mixed films showed a gel-like character and the elasticity evolved with adsorption time from values close to HPMC to values close to the protein.