| Driven by environmental concerns and a need to differentiate branded products from generic competitors, most laundry detergent products now contain enzymes (protease, amylase, and cellulase). The detergent market is also characterized by an increasing consumer preference for liquid products, which presents a formulation problem: enzymes must be shoehorned into an existing product that contains bleaches, surfactants, and as much as 1% protease. Thus, the goal of this research was to apply modern protein chemistry techniques to build a mechanistic understanding of enzyme activity loss in liquid detergent. Proteolysis, surfactant-induced unfolding, and calcium ion removal are all significant pathways for enzyme degradation.; Proteolysis can be problematic in any detergent formulation containing proteases. Experiments were conducted to measure protease degradation rates and catalytic efficiencies in whole detergent containing various thermodynamic stabilizers and enzyme inhibitors. This work emphasizes the conclusion that proteolysis rates can be slowed by both thermodynamic stabilization and kinetic inhibition.; Our work also examined how surfactants mediate enzyme degradation in detergent formulations. Surfactant monomers bind to proteins in a cooperative manner, causing unfolding and activity loss. Surfactant-induced unfolding is a thermodynamically favorable event, however, the kinetics of the unfolding reaction can be slowed significantly by: (1) modifying conditions to remove protein-surfactant electrostatic attraction, or (2) reducing the amount of surfactant monomer available to interact with the protein (e.g., by using mixed surfactants to lower the critical micelle concentration.); Surfactant aggregates hasten protease and amylase degradation in an indirect manner, by competing with the enzymes for their bound calcium ions. We show that calcium-free enzymes are more susceptible to proteolysis and/or surfactant-induced unfolding. This degradation pathway can be effectively blocked by adding calcium to a detergent formulation or by using surfactants such as ethoxylates that do not interact strongly with Ca2+ ions. |
