Abstract:

Alkaline protease is the most widely used enzyme in liquid detergents. The alkaline protease used in detergent industry accounts for more than 60% of the alkaline protease market. Different from the enzyme in powder detergents, which is wrapped due to granulation, the alkaline protease in liquid detergent is directly exposed to the solution and interacts with various deactivators such as surfactants, builders and bleaching agents. Anionic surfactants can cause significant changes in the conformation of alkaline protease, bleaching agents can partially oxidize the active center of protease, and chelators will compete with protease for Ca²⁺ to stabilize its active conformation, all resulting in the decline of washing stability of alkaline protease. In addition, the alkaline protease in liquid detergents suffers from the autolysis which can be enhanced by other deactivation factors, leading to an adverse effect on its washing performance. The stabilization of alkaline protease has been a hot topic. Researchers have made a lot of efforts on improving the stability of protease, which can improve the performance of enzyme preparation, reduce production costs and improve economic benefits. Extremozymes isolated from high or low temperatures, high salinity or alkaline environment have great potential in detergent industry, but it still needs a long time for industrial application because of the high cost of separation and cultivation. Herein, the catalytic and inactivation mechanisms of alkaline protease have been introduced, and the Ser-His-Asp catalytic triad is the key to the peptide bond hydrolysis activity of alkaline protease. Typical strategies for the stabilization of alkaline protease have been reviewed, including adding stabilizers, molecular modification and chemical modification. Adding stabilizers is the simplest but effective way to stabilize protease, and the stabilization effect of multi-component system is often better than that of a single stabilizer. Molecular modification is a new method of enzyme stabilization with high technical threshold, and the modification is not targeted at the enzyme itself, but involved in the process of enzyme translation, synthesis and expression. Chemical modification is a traditional strategy to improve the stability of enzyme, but seldom used for the enzymes for washing. Special attention has been paid to the introduction and comparison of polyethylene glycol modification and glycosylation modification. Finally, future perspectives of the stabilization stratagies for alkaline protease have been provided.

Key words: alkaline protease, liquid detergent, stabilizer, molecular modification, chemical modification