title: Thermodynamic incompatibility and complex formation in pectin/caseinate mixtures.
abstract: The instability of polysaccharide/protein mixtures occurs because of either thermodynamic incompatibility or complexation. We studied which instability mechanism dominated given the external conditions. Therefore the effect of temperature, pH, and biopolymer concentration on the phase separation of pectin/caseinate mixtures was investigated. At pH > 6, thermodynamic incompatibility with spinodal decomposition was observed in pectin/caseinate mixtures resulting in the formation of water-in-water emulsions in intermediate stages of the phase separation process. The demixing rate of these emulsions and appearance of two macroscopic phases (lower phase enriched with caseinate and upper phase with pectin) was retarded when the pectin concentration increased or when the storage temperature decreased due to a higher viscosity of the mixtures at those conditions. As the pH of the mixture was lowered below 6, pectin accumulated in the caseinate-rich phase. Complexation of pectin and caseinate led to the formation of microparticles (approximately 3 microm), whose shape depends on the biopolymer concentration ratio and rate of acidification. These pectin/caseinate particles do not coalesce and are insensitive to salt addition.
authors.affiliation: Department of Pharmaceutical Sciences, University of São Paulo (FCFRP-USP), Avenida do Café s/n, Ribeirão Preto, SP, Brazil.
authors.forename: Camila F
authors.initials: CF
authors.lastname: Rediguieri
authors.forename: Osvaldo
authors.initials: O
authors.lastname: de Freitas
authors.forename: M Paul
authors.initials: MP
authors.lastname: Lettinga
authors.forename: Remco
authors.initials: R
authors.lastname: Tuinier
mesh_terms: D000818:Animals; D002364:Caseins / Q000737:chemistry* / Q000378:metabolism*; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010368:Pectins / Q000737:chemistry* / Q000378:metabolism*; D044367:Phase Transition; D011485:Protein Binding; D013696:Temperature; D013816:Thermodynamics; D014783:Viscosity
chemical_list: D002364:Caseins; D010368:Pectins