The effect of polyelectrolyte dosage on floc formation in protein precipitation by polyelectrolytes

Abstract

Precipitation by polyelectrolytes is an important method in the processing of protein products. In the present work the effect of polymer dosage on floc formation was examined in the system consisting of lysozyme precipitated with polyacrylic acids. Precipitation was first done over a wide dosage range in small centrifugal tubes, and was conducted later at selected dosages in a stirred tank using an agitation schedule that induces floc aggregation, breakup, and re-aggregation in sequence. Protein recovery and precipitate properties, including floc composition, floc zeta potential, floc size distribution and floc strength as well as the reversibility of floc aggregation and floc breakup, were examined. Within a small dosage range, protein recovery has a linear dependence on polyacrylic acid (PAA) dosage and is independent of PAA molecular weights. At large dosage levels, the decrease in protein recovery with polymer dosage is less significant for PAAs of smaller molecular weight, and eventually disappears when the PAA of the lowest molecular weight is used. Two regimes of constant floc composition were observed within the small and large dosage ranges. and were independent of polymer molecular weight. With the PAA of the lowest molecular weight used, floc strength appears to be independent of polymer dosage, and floc size appears to depend on polymer dosage through protein recovery. With the PAA of the highest molecular weight used, flocs formed are weak at a small dosage, and are very strong at large dosages. The results suggest the importance of the polymer addition process in determining the mechanism of floc formation.