Neutral Protease Assisted Low-sulfide Hair-save Unhairing Basedon pH-sensitivityof Enzyme

Abstract

The mass transfer of protease in hide during enzymaticunhairing was first investigated by fluorescent tracer technique.It was found that the penetration rate of protease in hide wasquite slow, and protease remained on the grain/papillary layereven after removal of hair, which is the main reason whyenzymatic unhairing may cause grain damage or loose grain.But protease could effectively remove epidermis in a short time.From these phenomena, we developed an enzyme assisted lowsulfidehair-save unhairing (EALS unhairing) based onpH-sensitivity of neutral protease activity. To avoid risk of hidedamage, soaked cattle hide (pH 8) was first treated with neutralprotease (20 units/g hide) for 40 min at 22oC to cleave epidermisbut not to unhair, and then 1% lime was immediately added bothfor inactivation of the neutral protease (pH>12) and for hairimmunization. Finally, the hide was completely unhaired byusing 0.8% sodium sulfide with intact hair shaft. The smartlycontrolled action of protease, as well as the synergistic effect ofprotease, lime and sulfide, ensured the complete removal of hairand epidermis with reduced offer of chemicals, and preventedpelts from defects. The crust leather processed by using EALSunhairing had a cleaner grain surface compared with that usingconventional sulfide-lime unhairing. Additionally, the physicalproperties of the leather processed with EALS unhairing werecomparable to those of conventional leather. Sulfide, total solids,suspended solids and chemical oxygen demand in the EALSunhairing effluent were markedly reduced due to a dramaticdecrease in the input of sodium sulfide and lime as well as therecovery of hair.