Influence of pH and iota-Carrageenan Concentration on Physicochemical Properties and Stability of beta-lactoglobulin-Stabilized Oil-in-Water Emulsions

摘要

The influence of pH and iota-carrageenan concentration on the properties of beta-lactoglobulin (beta-Lg)-stabilized oil-in-water emulsions was investigated by measuring the particle charge,particle size distribution,and creaming stability.Emulsions containing droplets stabilized by beta-Lg were produced by homogenization,and then,iota-carrageenan was added.At pH 3,the droplet charge did not change for iota-carrageenan concentrations <0.1 wt % but decreased rapidly at high concentrations,while the mean particle diameter increased slightly as the iota-carrageenan concentration was increased.These results suggest that the interaction between iota-carrageenan and beta-Lg was weak at pH 3 probably because some sulfate groups were protonated (pK_a =2).At pH 4 and pH 5,the droplet charge decreased dramatically as the iota-carrageenan concentration was increased from 0 to 0.15 wt %,but droplet aggregation and creaming occurred in the emulsions,indicating that interfacial complexes between iota-carrageenan and beta-Lg could not stabilize the emulsions,probably due to bridging flocculation.At pH 6,the droplet charge in the primary emulsions was negative and became more negative as the iota-carrageenan concentration was increased.The mean particle diameter was relatively small at all iota-carrageenan concentrations,and emulsions were stable to creaming after 1 week of storage.We propose that carrageenan adsorbed to the droplet surfaces and increased the electrostatic repulsion between droplets.At pH 7 and pH 8,the droplet charge did not change as the iota-carrageenan concentration was increased,but these emulsions became unstable to creaming above a critical carrageenan concentration,which was attributed to depletion flocculation.