Phase-separated biopolymer mixture rheology: Prediction using a viscoelastic emulsion model

The relationship between the morphology and rheology of phase-separated bio polymer mixtures is investigated. Biopolymer mixtures, which are utilized i n the food industry for their textural and structuring properties, often ph ase separate and demix to form water-in-water emulsions. Controlling the mo rphology of biopolymer mixtures during flow processing and inducing gelatio n of one or both phases lead to products with novel microstructures and mat erial properties [B. Wolf et ai., Food Hydrocolloids 14, 217-225 (2000)]. A n emulsion model [J. F. Palierne, Rheol. Acta 29, 204-214 (1990)], commonly used for the prediction of the linear viscoelastic properties of polymer b lends, is used here to relate the rheology to the morphology of water-in-wa ter emulsions. The system under investigation is a gelatin-maltodextrin mix ture which phase separates at 60 degreesC for particular concentrations, ch aracterized by a binodal curve, into a gelatin-rich and maltodextrin-rich p hase. Emulsions with phase volumes of 10% and 30% were examined with either phase as the dispersed phase. The morphology varies with the preshear rate such that the radius of droplets after a preshear of 10 s(-1) is around 20 -50 mum while after a preshear of 100 s(-1) the droplets are typically less than 10 mum. Despite the low viscosity, elasticity, and interfacial tensio n of the gelatin-maltodextrin emulsion, the emulsion model is found to pred ict the rheology and morphology of the mixtures subjected to preshear rates of 1-100 s(-1). The interfacial tension for the gelatin-maltodextrin syste m studied is approximately 50 muN/m at 60 degreesC. (C) 2001 The Society of Rheology.