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 f rom a protein precipitate suspension prepared from disrupted yeast. The eff ects of the process parameters transmembrane pressure (TMP), crossflow velo city, and suspension concentration on the permeate flux and transmission (s ieving coefficient) of soluble proteins were determined. Flux increased wit h increasing crossflow velocity and decreasing concentration, and increased with increasing TMP up to a critical value at which the flux became indepe ndent of pressure. Protein transmission also increased with increasing cros sflow and decreasing concentration, but had a maximum value at a critical T MP, near the critical value for flux, and declined at higher pressures. A s imple 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 fa ctors: increasing protein concentration at the membrane surface and decreas ing intrinsic transmission (i.e., transmission calculated with respect to t he concentration at the membrane surface). Although flux and transmission b oth increased with decreasing concentration, it was found that an intermedi ate concentration gave the best rate of soluble protein recovery. Differenc es were also noted between the transmission of a target enzyme, alcohol deh ydrogenase (ADH), and the overall transmission of total soluble protein.