Extending foam fractionation to non-foaming proteins.

摘要

Foam fractionation is an inexpensive way to concentrate proteins from an aqueous solution. Yet, foam fractionation has two major drawbacks. One drawback is that it cannot work effectively with hydrophilic proteins because hydrophilic proteins generally do not foam when aerated. Examples of such "non-foaming" proteins are lysozyme and cellulase (both used with a detergent additive as model proteins in this study). The second drawback is that proteins can undergo a structural change when adsorbed on a gas-liquid interface during foaming. Changes in protein structure can lead to a loss of the protein functionality such as the activity (when the protein is an enzyme), as is the case for cellulase. The main subject for exploration in this dissertation is that of overcoming these two drawbacks of foam fractionation. With the addition of a detergent to a protein solution, foam can be created from a hydrophilic protein solution much in the same way as a hydrophobic protein, such as bovine serum albumin. This generation of foam makes it possible to extend the application of a foam fractionation process to non-foaming proteins. When cellulase is foamed in the presence of a detergent, some of the cellulase activity lost in that foaming process can be regained by adding beta-cyclodextrin to the recovered foam (the foamate). One effective detergent for the cellulase foaming process is cetyltrimethylammonium bromide (CTAB). It takes less than an hour to restore the lost activity from a CTAB-assisted foam fractionation of cellulase after beta-cyclodextrin is added to the foamate. Using CTAB and beta-cyclodextrin together it is possible to double the cellulase concentration when compared to the original solution, while retaining about 70% of the original enzymatic activity. For the detergent-assisted foam fractionation of lysozyme process, sodium dodecylsulfate (SDS), detergent-assisted foam fractionation provides the highest enrichment and recovery (and without any loss of activity) of the three detergents tested (CTAB, SDS and Pluronic F-68). beta-cyclodextrin did not need to be added following the SDS-assisted foam fractionation of lysozyme process because there was no loss of lysozyme activity.