Protease stabilization by highly concentrated anionic surfactant mixtures

Abstract

AbstractWe have found that anionic surfactants such as linear alkylbenzene sulfonate (LAS) can solubilize proteases in a substantially nonaqueous environment without loss of proteolytic activity. Moreover, in mixtures of anionic and nonionic surfactants with a moderate amount of water (water less than 30 wt%), controlled levels of LAS and water solubilize proteases; yet, in these concentrated surfactant mixtures, enzymes maintain their activity for extended periods. Experimental design techniques have been used to delineate the relationship between protease stability and the water, pH and anionic surfactant levels in these surfactant concentrates. As the sum of water and LAS levels is increased, maximum enzyme stability is observed, after which stability falls off. At low water and LAS levels (sum of both <20%), protease solubility is low, while at high levels of water and LAS (sum of LAS and water >45%), denaturation predominates. Additionally, we have developed a new and simple method to predict protease stability by which a synthetic peptide is used to measure protease activity directly in the surfactant concentrate. From the application of this new technique to our system and to commercial liquid detergent formulations, it is apparent that water facilitates the loss of activity of proteases in surfactant concentrates by increasing the rate of autolysis.