Effects of Emulsification of Fat on the Surface Tension of Protein Solutions and Surface Properties of the Resultant Spray-Dried Particles

Abstract To examine the effect of protein adsorption on the fat–water interface on the surface composition of spray-dried particles, whey, hydrolyzed whey, and soy protein isolate emulsions were prepared at three different protein to fat ratios of 1:1, 1:5, and 1:10 and spray dried. Non-hydrolyzed whey protein isolate (WPI) and the more hydrolyzed whey protein solutions at 20.2% degree of hydrolysis (DH) had significantly lower surface tension values with fat than without fat. The correlation between the reduction of surface tension value of an emulsion and the increase in protein surface composition of powder particles was observed for WPI and HWP406 but was not observed for the other protein isolate types. It was clear that the spray-dried emulsions had fat as the dominant component on the surface of the powder particles and that the amount of protein on the surface became severely depressed at higher fat addition levels. In terms of its powder morphology, the unique powder structures such as the indentations and folds usually found on the surface of protein containing powders were not evident because they were compromised by the presence of high surface fat. The powder with higher surface fat had more crumpled particle structures and dimpled surfaces. Keywords: EmulsionFatFood proteinsHydrolysisPowderSEMSoy proteinSurface activitySurface tensionWhey proteinWilhelmyXPS ACKNOWLEDGMENT The authors acknowledge the facilities, and the scientific and technical assistance, of the Australian Microscopy & Microanalysis Research Facility at the Centre for Microscopy and Microanalysis, The University of Queensland. Notes Surface tension values followed by different superscript letters within each column are significantly different (P < 0.05) from each other. Surface tension values followed by different superscript letters within each column are significantly different (P < 0.05) from each other. Mean droplet size values followed by different superscript letters within each column are significantly different (P < 0.05) from each other. P = protein, F = fat.