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A two-stage aqueous phase extraction of the enzyme fumarase from baker's yeast is described with respect to the recycling of the upper effluent phase from the secondary extraction. It was found that the binodal curve position was only slightly altered by the presence of protein at different load levels and that enzyme specific activity in the product was improved at higher total protein concentrations, which simplified the recycling strategy. On-line enzyme and protein assays showed that disturbances during start-up and desludging operations were reflected in variations in the protein concentrations in the various streams, but that the enzyme activities remained relatively stable. Recycling reduced the polyethylene requirements by 50% and that for potassium phosphate by 12%. A maximum saving of PEG (polyethylene glycol) of approximately 70 YO was achieved at optimum conditions of extraction, compared to a value of 90% predicted by a theoretical description of the system. An economic analysis of the recycled process showed significant advantages compared with a non-recycled system, even though the capital outlay requirements for an automated, continuous system are much higher than for a manually run process.

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