Effect of cloud particle characteristics on the viscosity of cloudy apple juice

Particle size, shape, and volume fraction as well as soluble pectin content and electro-viscous effects on cloudy apple juice viscosity were investigated. Particle characteristics were micrographically determined by electron microscopy. More than 2300 particles were digitalized and statistically analyzed. Cloudy apple juice resulted in a suspension of irregular shape particles ranging from 0.25 to 5 mu m in size. A 10 degrees Brix juice had a particle volume fraction of phi(0) = 3.93 x 10(-3). Relative viscosity values were fitted to the generalized Sudduth equation. Intrinsic viscosity resulted 5.8 times greater than the theoretical value predicted by Einstein (alpha = 2.5). This was attributed to the first electro-viscous effect. Results also indicate that the effect of particle non-sphericity on cloudy apple juice viscosity can be neglected. Soluble pectin was found to increase juice viscosity significantly. Combined effects result in a strong linear increase of relative viscosity.