Alkaline protease for an efficacious rehydration of skin matrix by a novel Bacillus crolab MTCC 5468 in sustainable leather production: a green approach

Abstract

Objectives

The utilization of biotechnology in leather sector has more extensive in modern years; more particular to proteolytic enzymes and employed in several steps of the leather making such as soaking, dehairing, bating, solid waste management etc. The current study evaluates the performance of alkaline protease from Bacillus crolab MTCC 5468 in single soaking of goat skins matrix by comparing with the conventional multiple soaking processes.

Results

According to the obtained results, the optimum concentration for maximum rehydration of goat skins was accomplished at 1.0% (v/w) of alkaline protease at duration of 3 h over traditional rehydration method (4–6 h). The moisture level, total protein, chloride content and total organic carbon of enzymatic rehydration was superior to that of conventional rehydration and it was also used to measure the effectiveness of rehydration process. Scanning electron microscopic images of enzymatically processed leather exhibits enhanced opening of fiber bundles and smooth grain surface than conventional method. Furthermore, the alkaline protease treated leather exhibited improved moisture uptake, removal of chlorides and suppleness because of hydrolysis of non-collagenous proteins as indicated by well opened up fiber bundles in histological analysis.

Conclusions

The application of alkaline protease in rehydration operation of leather production confirmed scope for diminishing water quantity around 66.6%, soaking duration at 50%, minimizing use of harmful dehairing chemicals at 50–60%, thereby, eliminating the bating operation during pre-tanning. These outcomes suggest that alkaline protease have potential application in rehydration of skins for immense environmental concerns of leather tanning sectors.

Graphic abstract

Appendices

Appendix 1

The soaked goat skins from conventional were subjected to unhairing using 3% (w/w) sodium sulphide and lime 10% (w/w) whereas, partial unhairing chemicals (sodium sulphide 1.5% (w/w) and lime 5%(w/w)) were used for experimental skins. After unhairing all goat skins were relimed using 10% lime and 150% water for 48–72 h. These relimed goat skins were defleshed (sub-cutaneous tissues) using fleshing machine. After defleshing, the skins were delimed using 1% (w/w) ammonium chloride with 100% water (v/w) for 45 min in rotating drum, followed by treatment with 1% (w/w) alkali bate for 30 min in conventional method. After bating operation, the goat skins were washed two times and drained out. The washed skins were pickled using 8% (w/w) common salt and 80% (v/w) fresh water and run for 10 min followed by acidification using 0.5% (v/w) formic acid was mixed with 10% (v/w) water and given for 2 feeds at 10 min interval and run for 15 min, then 1% (v/w) sulphuric acid was mixed with 10% (v/w) water and given for 4 feeds at every 10 min intermission and the drum was additional run for 60 min. The final pH of pickled goat skin was 2.8 and the pickled skins were tanned using 8% (w/w) basic chromium sulphate (BCS) for 2 feed in half of the pickle bath for 90 min, then 50% (v/w) water was added and run for 30 min. After two feed of BCS, was basified using 1% (w/w) sodium formate was mixed with 10% (v/w) water and added to the rotating drum and then 1% (w/w) sodium bicarbonate was mixed with 10% (v/w) water and fed in 3 parts at 10 min intervals. Then, drum was continuously run for more than 60 min for additional fixing of tanning material. After chrome tanning operation, the pH of the both liquor and wet blue was observed to be 3.8.

Appendix 2

The wet blue leather was washed with 100% (v/w) water in a drum for 10 min, the water was drained out and wet blue leathers were treated with neutralizing syntan 1% (v/w) in 100% (v/w) float in a drum and run for 20 min. After this, 0.5% (w/w) sodium formate and 0.5% (w/w) sodium bicarbonate were added to the running drum in 3 feeds at 10 min time interval. After the liquor accomplished a pH of 5.0, the wet blue leathers were washed twice with water 200% (v/w) for 10 min. After completion of washing, 100% (v/w) water with 3% (w/w) resin syntan were added to the drum and run for 20 min. Followed by this, dying was carried out using 2% (w/w) acid dye for 30 min and fat liquoring was carried out with synthetic fat liquor 4% (w/w) in the drum for 30 min. Subsequently, melamine based re-tanning syntan 4% (w/w) was added and run for 40 min followed by the addition of synthetic fat liquor 4% (w/w), polymeric fat liquor 3% (w/w) and natural fat liquor oil 4% (w/w) and further running the drum for 40 min. Finally, the auxiliaries were leather was fixed using 2% (v/w) formic acid diluted with 20% (v/w) water and added at 3 feeds at every 10 min interval and the drum was further run for 30 min. After this, the leather was piled overnight and were subjected to setting and hooked for drying. The dried crust leathers were staked and buffed using 400 grit emery papers.