Influence of chitosan concentration on the stability,microstructure and rheological properties of O/W emulsions formulated with high-oleic sunflower oil and potato protein |
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Authors: | Nuria Calero,José Muñ oz,Phil W. Cox,Alex Heuer,Antonio Guerrero |
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Affiliation: | 1. Departamento de Ingeniería Química, Facultad de Química, Universidad de Sevilla, c/P. García González, 1, E41012 Sevilla, Spain;2. Centre for Formulation Engineering, School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK |
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Abstract: | Relatively concentrated (40 wt%) O/W emulsions formulated with high-oleic sunflower oil as disperse phase, potato protein isolate as emulsifier and chitosan as stabiliser were prepared by rotor–stator/high-pressure valve/rotor–stator homogenization. The influence of chitosan concentration on the physical stability of emulsions was studied in (0.25–1) wt% range by visual inspection, rheological and microstructural techniques. Steady shear flow curves were sensitive to the occurrence of creaming upon the rise of zero-shear viscosity values. The effect of increasing concentration of chitosan on the zero-shear viscosity turned out to be dependent on emulsion ageing and always resulted in a stepwise increase of the critical shear rate for the onset of shear thinning flow. The critical oscillatory shear stress for the onset of non-linear viscoelastic behaviour was more sensitive than the critical shear rate to detect creaming in emulsions. Mechanical spectra are definitely demonstrated to be the most powerful tool to detect not only creaming but also oil droplet flocculation on account of changes in the plateau relaxation zone. CSLM micrographs supported the interpretation of dynamic viscoelastic results, especially when flocculation as well as coalescence took place. Cryo-SEM micrographs evidenced the formation of increasingly denser protein–polysaccharide networks with chitosan concentration and the fact that the latter governs the microstructure of the emulsion when reaches 1 wt% concentration promoting enhanced physical stability. |
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Keywords: | Chitosan Potato protein isolate Emulsion Rheology Cryo-SEM CLSM |
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