Effect of Electrostatic Interaction between Collagen and Enzymes on Permeation of Protease into the Pelt during Leather Bating Process

The enzymatic delimed pelts bating process using proteases is critical to improving the overall performance of the leather. Bating effectiveness is determined not only by the properties but also by the permeation behavior of the proteases. Imperfect methods to control protease permeation often results in uneven distribution of enzyme proteins in the pelts, leading to excessive enzymolysis of the surface layer and inadequate opening-up of the inner layer. In this study, the relative size of proteases and delimed pelts were analyzed, the permeation behavior of fluorescein-labeled proteases in the pelt was observed using a confocal laser scanning microscope (CLSM), and the effect of electrostatic interaction between protease and collagen proteins on the permeation of protease into the pelt was investigated. The results showed that, after dehairing, liming and deliming operations, the enzyme can easily permeate into the pelts due to the formation of large cavities and interfibrillar gaps. The permeation of protease within the delimed pelt is significantly influenced by the affinity (electrostatic interactions) between the collagen and protease proteins. The isoelectric point (pI) of the protease protein, the collagen and the pH of the solution directly influence the electrostatic properties and interactions. When the enzyme and collagen are similarly charged (electrostatic repulsion), the enzyme can easily permeate into the pelts; when the enzyme and collagen are oppositely charged (electrostatic attraction), the permeation of the enzyme into the inner layer is difficult, resulting in the accumulation of protease on the grain and excessive hydrolysis of the grain layer. Therefore, the established permeation regulation mechanism of protease based on electrostatic interactions between enzyme and collagen could serve as an important basis for the selection of protease and the regulation of the enzymatic bating process.