Study On The Relationship Between The Change Of The Structure Of The Hide And The Performance Of The Leather Influenced By Protease

In recent years,enzymatic unhairing has attracted the attention of lots of reserachers,because of the large amount of pollution caused by traditional sodium sulfide unhairing method.Owing to high substrate specificity,enzymatic unhairing is prospected to replace the traditional chemical method,which degrades disulfide bonds by sodium sulfide.The utilization of enzymatic unhairing not only reduces the sulfur pollution caused by the traditional unhairing,but also utilizes the removed hairs.Therefore,enzymatic unhairing is worth to explore and develop as an environmentally friendly technology.This research studied the application of Wb600-KerT in enzymatic unhairing of goat skin,exploring suitable condition and constructing the initial process.In the previous study,our research team obtained a strain of Bacillus amyloliquefaciens TCCC 11319,which can produce keratinase and collagenase.The keratinase KerT is high producing gene.By gene modification,its gene was heterologously expressed in Bacillus subtilis WB 600 that of lacking six extracellular protease genes,and then obtained a novel unhairing enzyme Wb600-KerT which can be utilized for hair removal.The activity of collagenolytic protease was obviously inhibited.In leather production,it is well known that the surface of skin may be damaged when high concentration of collagenase exists.Hence,as a key component in enzyme unhairing should be taken seriously.Therefore,this study utilized fluorescence spectroscopy and simultaneous fluorescence spectroscopy to study the reaction mechanism between collagenase and collagen.According to considerable partial buried by the self-assembly of collagen,the intrinsic fluorescence of collagen may decrease and represented the decline of its binding sites.When introducing low concentration of collagenase,the intrinsic fluorescence and synchronous fluorescence of collagen increased with the addition of more collagenase,it leaded to more binding sites exposed which contributed to the combination of agents in subsequent processes.Therefore,the concentration of collagenase in unhairing enzyme should be controlled with low level rather than fully eliminated.Further,Wb600-KerT has a low collagenase content thus it is worthy to be applied in unhairing process as a novel potential enzyme.The conventional sodium sulfide unhairing and several enzymes assisted unhairing menthods were compared with Wb600-KerT unhairing.When compared to X-Zyme 4072,the collagenase percentage in Wb600-KerT is only 70%of in X-Zyme4072 when they keep the same keratinase activity.In unhairing,when the kerainase activity of Wb600-KerT is 2520 U/g,it should not be used more than 0.1%?w/w?.Otherwise,it will damage the grain surface and reduce low quality of leather.The Wb600-KerT can be used in unhairing with a small amount of Na₂S because Na⁺can activate Wb600-KerT.Hence,it obtains good removal of hair with the usage of 0.5%Na₂S combined with Wb600-KerT.The amount of Na₂S was successfully reduced compared to commercial enzyme assisted agent?1.0%Na₂S+0.5%NaHS?and traditional unhairing?2.5%Na₂S?.After aldehyde-tannin combination tanning,soft crust leather is obtained.Its shrinkage temperature is 96?and the tear strength is15.06 N/mm.In furture study,the unhairing process will be optimized,the usage of Na₂S is expected to be lower.This study was a start-up exploration for the application of Wb600-KerT in unhairing process,it has a significant guidance for enzyme unhairing applied in future industrial leather production.