Effect of surface tension and viscosity on the surface stickiness of carbohydrate and protein solutions

The effects of surface tension and viscosity on the measured tensile strength (surface stickiness) of carbohydrate (fructose, lactose and maltodextrin) and protein (Whey protein isolate (WPI)) solutions were studied. The effect of the addition of WPI on the surface tension and surface stickiness of lactose solutions was measured. Surface tension was found to better correlate with surface stickiness compared to viscosity. Cohesive failure occurred in all the cases indicating that the energy required to create new surfaces within the drops was lower than the energy required to achieve a clean (adhesive) failure at the probe-drop interface. WPI behaves as a surfactant and sharply lowers both the surface tension and tensile strength. This study shows that the surface forces are more dominant than the theological forces when the energy required to create new surface within the drop is less than the adhesive energy at the drop-probe interface. (c) 2006 Elsevier Ltd. All rights reserved.