Ultrasonic attenuation spectroscopy study of flocculation in protein stabilized emulsions

The extent and kinetics of droplet flocculation in emulsions was studied us ing ultrasonic attenuation spectroscopy. Flocculation in 10 wt.% soybean oi l-in-water emulsions, stabilized by whey protein isolate (0.75 wt.%), was c ontrolled by adjusting the pH (between 3 and 7) to alter the electrostatic interactions between the droplets. Droplet flocculation was then monitored by measuring the ultrasonic attenuation spectra (1-150 MHz) and by using la ser light scattering. Extensive droplet flocculation was observed in the em ulsions around the isoelectric point of the proteins (pH 3.5-5.5). Floccula tion caused an appreciable change in the ultrasonic attenuation spectra, wh ich was in good qualitative agreement with a theory recently developed to d escribe the ultrasonic properties of flocculated emulsions. Our results ind icate that ultrasonic spectroscopy is a powerful tool for monitoring both t he extent and kinetics of flocculation in concentrated emulsions in situ. ( C) 1999 Elsevier Science B.V. All rights reserved.