Effects of bactericide–protease interactions on the protease-assisted soaking performance

Protease-assisted soaking has received increasing attention in recent years. However, few reports have elaborated on the effect of bactericides, which are used to protect raw hides from microbial damage in the soaking process, on the performance of protease-assisted soaking. Here we investigate the effects of three bactericides, namely, 2-methyl-4-isothiazolin-3-one (MIT), sodium propyl 4-hydroxybenzoate (SPHB) and cetyl trimethyl ammonium bromide (CTAB), on the catalytic activity of protease. MIT and SPHB have little effect on the proteolytic activity, whilst CTAB has a negative effect. Fluorescence spectroscopy, synchronous fluorescence spectroscopy, molecular docking and molecular dynamics simulation were used to analyse the bactericide–protease interaction. The data reveal that MIT and SPHB are bound to the non-catalytic sites of protease, whilst CTAB affects the catalytic triad of protease. Furthermore, the protease and bactericides were used alone, simultaneously and sequentially in the soaking process, and their soaking performances were evaluated. The evaluation shows that the use of protease increases the microorganisms in the soaking float, and MIT exhibits the best bactericidal effect. The simultaneous use of protease and MIT effectively inhibits bacteria and scarcely affects the removal of unstructured proteins from hides and the attack on epidermis by protease. These findings contribute to a better understanding of the scientific use of protease with other auxiliaries in soaking.

Graphical Abstract