An Integrated Two-Step Enzymatic Unhairing Strategy: Eliminating the Penetration Barrier via Soaking To Enhance Targeted Protease Action

To address the limitations of enzymatic unhairing, including prolonged unhairing cycles, low efficiency, and potential grain damage, the hydrolytic properties of typical keratinases toward major structural proteins in bovine hides were investigated. Their effects on hide pretreatment, enzymatic unhairing efficiency, and leather quality were also assessed. The results show that the differential hydrolytic intensity of keratinase toward hide structural proteins directly determines its pretreatment performance. The activity ratios are calculated based on the hydrolytic activities toward structural proteins normalized to casein hydrolysis activity under identical assay conditions. A keratinase with specific activity ratios of approximately 0.034 for keratin, 1.905 for collagen, and 0.002 for elastin effectively removed the epidermis during the soaking process while moderately hydrolyzing collagen and elastic fibers. This pretreatment opened intradermal penetration channels. Consequently, the time required for unhairing proteases to reach hair follicle targets was reduced from more than 3 h to less than 1 h, which significantly improved the enzymatic unhairing efficiency. Based on these findings, an enzymatic unhairing strategy integrating keratinase pretreatment with targeted action of unhairing proteases was developed. This approach shortens the enzymatic unhairing process by more than 50%. It also limits excessive protease action on the hide surface and significantly improves leather quality. These results provide valuable guidance for the development of keratinases and the design of integrated enzymatic soaking–unhairing technologies.