RHEOLOGY OF LECITHIN DISPERSIONS

Dispersions of lecithin (1-25% solids, dry basis) in soybean oil or wa ter were subjected to rheological measurement in a coaxial-cylinder vi scometer. The different rheological characteristics determined include d yield stress, flow behavior index, consistency index, and apparent v iscosity. Pseudoplastic behavior was observed for all lecithin emulsio ns in oil and for dispersions in water. The flow behavior indices for lecithin-oil emulsions (0.855-0.875) were higher than for lecithin-wat er dispersions (0.472-0.584). Yield stresses were observed only for le cithin-water dispersions. An increase in the concentration of lecithin in oil or water increased yield stress, consistency index, and appare nt viscosity. The apparent viscosities of the lecithin-oil emulsions w ere higher than those for corresponding lecithin-water dispersions. Th e power law model can adequately fit (r greater than or equal to 0.988 , P less than or equal to 0.01) the shear-rate vs. shear-stress data f or lecithin-oil emulsions, whereas the Herschel-Bulkley model was suit able (r greater than or equal to 0.988, P less than or equal to 0.01) for lecithin-water dispersions.