Possibilities for recycling cellulases after use in cotton processing
Repeated treatments on cotton fabrics, using a total cellulase from Trichoderma reesei, showed that active enzymes remained in the treatment liquor and adsorbed on the fabric substrates after five treatment cycles. The activity (measured as fabric weight loss) of the cellulases remaining in solution, however, decreased by 80% over the five cycles. It was suggested that this could be due to end-product inhibition, thermal and or mechanical deactivation, or to the loss of some components of the cellulase complex by preferential and irreversible adsorption to the cotton substrates. End-product inhibition studies showed that the build-up of cellobiose and glucose in solution would cause less than 25% activity loss after five treatment cycles. Agitation levels similar to those used in textile processing did not cause significant cellulase deactivation, but incubation of total cellulase solutions for 5h at 50 °C (equivalent to five treatment cycles) reduced their activity by about 20%. Analysis of cellulase solutions, by fast protein liquid chromatography, before and after adsorption onto cotton, suggested that the cellobiohydrolase II content of the cellulase complex was reduced, relative to the other components, by preferential adsorption. This would lead to a marked reduction in activity in the supernatant after several treatment cycles and top-up with pure cellobiohydrolase II would be necessary unless this component is easily recoverable from the treated fabric. Although desorption studies showed that much of the adsorbed cellulase protein was recoverable by washing in buffer solution, concentration of the washings by ultrafiltration needs to be carefully costed. Experiments with pure endoglucanases, with and without their cellulose binding domains, suggested that desired cotton finishing effects might be achievable using only cellulase components that are adsorbed reversibly. These would be ideal for recycling. Ultrafiltration was used successfully to reduce end-product concentrations in treatment liquors, but this technique failed to separate dyes from cellulase proteins. Since dye-cellulase complexes cause backstaining problems, it seems unlikely that cellulases used for enzymatic stonewashing (currently the most important cellulase-finishing process) can be recycled unless a solution to this problem is found. Using only reversibly adsorbed cellulase components may be beneficial also in this context. Cost estimates suggested that when more than 100 to 125 tonnes per annum of cellulosic fabric are being treated with cellulases, the savings made by recycling enzymes would exceed the capital and running costs of the ultrafiltration unit required for their recovery and concentration.
Sousa Sepulveda Azevedo, Helena Paula de
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