High-efficiency Bio-degreasing Technology for Leather Making – Characterization of Catalytic Hydrolysis Properties of Lipases Towards Fats Based on Greasy Skin Powder Substrate

Abstract

Bio-degreasing technology based on the use of lipases has attracted more attention in the leather industry. Although lipases have been applied in leather making in the past, the previously reported lipase degreasing ratio is still not very high, i.e. less than 60%. In order to correctly understand the mechanism of lipase degreasing and to choose lipases and optimize the degreasing process for achieving efficient degreasing, a novel method of evaluating the catalytic hydrolysis properties of lipases towards skin fats based on a greasy skin powder substrate in an aqueous medium was established. This simulated the actual leather degreasing process and detected the amount of fatty acids produced. The special substrate was prepared; the determination conditions were optimized; then the performances of several typical lipases were evaluated. The results revealed that the lipase performances determined by the novel method were quite different from the standard method using emulsified olive oil substrate. There was a strong productinhibition characteristic in the catalytic hydrolysis reaction of lipase, and the inhibition concentration of fatty acids varied with the lipase type, thus the maximum hydrolysis ratio of fats was only 67%. The lipases exhibited “super activity” at pH around 9.5. This occurred because the fatty acids produced transformed into soluble soaps, thus the product-inhibition was weakened. According to the above results, a two-step lipase processing was made, i.e., beginning at pH 7.5 then 9.5. The hydrolysis ratio of fats rose to 82.57% from 46.23%, and the degreasing ratio increased from 50.78% to 89.68%. The new method with better repeatability can be used as a tool to correctly select lipases and optimize process parameters for lipase degreasing.