Interaction amongst calcium salts, trypsin, and hide proteins and its application for high-quality leather bating process

Bating animal hides with trypsin is an essential step for making leathers. But the mechanism why the calcium in the hide influences the bating performance remains unclear. Here, the enzyme activity of trypsin was determined using N-alpha-benzoyl-L-arginine ethyl ester, bovine albumin (BSA) and collagen fibres as substrates in the presence and absence of calcium salts. The interactions of calcium with trypsin, BSA and collagen were analysed by fluorescence spectroscopy and molecular docking. Data reveal that calcium which binds to BSA and collagen improves the structural stability and enzyme resistance of hide proteins. As a result, a high calcium content of delimed hide is useful to obtain an intact surface of bated hide. However, a low calcium content of hide for pickling is necessary for producing leathers with high physical properties and uniform colour. According to these results, a novel bating system involving deliming, bating and redeliming operations was developed. This system provides a high calcium content of hide for bating and a low calcium content of hide for subsequent pickling and tanning, which effectively reduces the risk of hide damage and improves the physical properties and colour uniformity of leather.