Enhancing Chrome-free Leather Quality through Enzymatic Bating Technology Ying Song, Lixiang Zhang, Yue Yu, Ya-nan Wang, Bi Shi and Yunhang Zeng

Abstract

Environmentally friendly chrome-free tannages are receiving increasing attention in the leather industry. However, their application is limited due to the generally inferior properties of chrome-free leathers compared to chrome-tanned leather. This study presents an effective method to improve the sensory and physical properties of chrome-free leathers. Three types of representative chrome-free tanned leathers, namely, vegetable-tanned leather (VTL), chrome-free metal-tanned leather (MTL), and aldehyde- tanned leather (ATL), were bated with proteases to improve the leather quality. Catalytic activity assays demonstrated that the vegetable tanning agent (ME) considerably inhibited the protease activity, whereas the chrome-free metal tanning agent (TWLZ) and aldehyde tanning agent (PAT) had no negative impact. Fluorescence and synchronous fluorescence spectroscopy analyses revealed that ME reduced the hydrophobicity of tyrosine and tryptophan residues, while TWLZ and PAT only slightly influence the conformation of protease, which may account for the observed changes in the protease activity. Influenced by the isoelectric points of protease and leather, as well as the bating pH, protease transferred slowly in the MTL, but rapidly in the VTL and ATL. The three enzymatic bated chrome-free leathers resulted in increased dye and fatliquor uptake, higher yield, enhanced softness, tensile strength, and tear strength, while maintaining the intact natural pattern and causing moderate collagen damage. These results indicate that enzymatic bating is a promising approach for improving the quality of chrome-free leather and broadening the application of chrome-free tannages.