Microfiltration of protein precipitate from clarified yeast cell homogenate for the recovery of a soluble product

A crossflow microfiltration unit was used to recover the soluble proteins from a protein precipitate suspension prepared from disrupted yeast. The effects of the process parameters transmembrane pressure (TMP), crossflow velocity, and suspension concentration on the permeate flux and transmission (sieving coefficient) of soluble proteins were determined. Flux increased with increasing crossflow velocity and decreasing concentration, and increased with increasing TMP up to a critical value at which the flux became independent of pressure. Protein transmission also increased with increasing crossflow and decreasing concentration, but had a maximum value at a critical TMP, near the critical value for flux, and declined at higher pressures. A simple analysis based on film theory indicated that the pattern of variation in measured transmission (i.e., permeate protein concentration divided by feed protein concentration) with increasing TMP was due to two competing factors: increasing protein concentration at the membrane surface and decreasing intrinsic transmission (i.e., transmission calculated with respect to the concentration at the membrane surface). Although flux and transmission both increased with decreasing concentration, it was found that an intermediate concentration gave the best rate of soluble protein recovery. Differences were also noted between the transmission of a target enzyme, alcohol dehydrogenase (ADH), and the overall transmission of total soluble protein.