In situ study of flocculation of whey protein-stabilized emulsions caused by addition of high methoxyl pectin

The effect of pectin addition to a 10% oil-in-water emulsion stabilized with whey protein isolate was measured in situ using Ultrasound (US) and Diffusing Wave Spectroscopy (DWS). At pH 7 changes in velocity of sound and in 1/l* were measured while adding pectin to the emulsion, indicating a change in the spatial organization of the droplets perhaps caused by a change in the hydration layer. At pH 3.5, sequential additions of pectin showed four different stages in the interactions between droplets. At very low concentration of pectin (<0.02%) no changes were observed, while at 0.02–0.04% pectin 1/l* decreased, perhaps indicating the occurrence of long-range interactions. Between 0.045 and 0.06% pectin, a dramatic change in velocity, attenuation and 1/l* occurred because of the change in hydration layer and surface charge distribution of the oil droplets. Finally, at high concentration of pectin (above 0.06%) bridging flocculation occurred leading to changes in droplet size and size distribution.