Use of certain alcohol ethoxylates to maintain protease stability in the presence of anionic surfactants

Anionic surfactants, including linear alkylbenzene sulfonate (LAS), are known to decrease the stability of detergent proteases, possibly by hastening autoproteolytic processes. Thus, protease shelf life in enzyme-containing, heavy-duty liquid laundry detergents (HDL) is typically maintained by adding stabilizers, by limiting the level of interfering anionics, or by utilizing more compatible anionics, such as a alcohol ethoxysulfates (AES). This study examines the stability of Savinase(R) detergent protease in HDL formulations based on LAS and containing different alcohol ethoxylates (AE) for protection against protease inactivation. Dose response curves demonstrated that all commonly used anionic surfactants exceptAES promote loss of protease activity. In HDL formulations with equal percentage compositions of LAS and AE, the structure of the selected AE was found to have a profound influence on protease stability, Inclusion of AE with chain length greater than or equal toC(14) and ethoxylate levels >70% resulted in greater protease stability. HDL containing LAS and these protective AE could be formulated to achieve protease stability matching those of simulated commercial products. Unlike polyhydric stabilizers, the AE by themselves confer no additional stability to the protease. It is more likely that the stabilizing effect of the protective AE is due to decreased availability of LAS to the protease.