Primary particle formation in protein precipitation

Recovery of proteins frequently involves a precipitation step in which ease of recovery of the solid protein depends on the size and density of the solid particles. The solid particles are actually aggregates of much smaller primary particles. In this work, possible influences on the aggregates of primary particle properties are postulated. The role of precipitation conditions during precipitation of soy protein with acid or CaCl(2) is determined by measurement of zeta potential and size distribution. Results are consistent with a nucleation/growth model for determination of size. There is indirect evidence that fractionation occurs at the primary particle level, although the particles are homogeneous at the aggregate level.