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In this work the effects of ι-carrageenan and κ-carrageenan on macroscopic properties of commercial sunflower oil/water systems, stabilised by whey proteins, were investigated by measuring the interfacial and bulk rheological properties, the particle size distribution and the creaming stability. The main aim was to investigate the relationship between interfacial characteristics and emulsion stability, evidencing the conditions to be used to improve the emulsion properties. Transient interfacial tension and dilatational dynamic moduli were measured with a “pendant drop” tensiometer; experimental results have shown that, in the investigated range, the carrageenan increases the interfacial tension and yields a more resistant layer surrounding the oil drops, mostly in the presence of ι-type. Bulk rheological tests carried out on emulsions, manufactured by using the same components and sunflower oil, have evidenced that the addition of the carrageenan to the protein system causes an increase of the emulsion viscosity and, as a consequence, a reduction of droplet movement and aggregation. The analysis of Drop Size Distribution (DSD), adopted to investigate the coalescence stability, evidenced that polysaccharide addition yields larger droplets but reduces significantly the change of polydispersity with time (within the tested range), suggesting greater emulsion stability. This result was also confirmed by an analysis of the “creaming index”, carried out measuring the separated cream layer of samples stored up to 24 h: low values were obtained when carrageenan was used. Moreover, it was observed that stability improves significantly by adding ι-carrageenan rather than κ-carrageenan. Finally, experimental results have shown that DSD seems more affected by interfacial tension values, whereas stability is dependent on the viscoelasticity of the interfacial layer. |
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