The glycoconjugates, herein glyco-proteins, existing in animal skins are closely related to the effectiveness of unhairing and fiber opening-up. Glycosidases have been used in leather making processes to reduce pollutants and improve leather quality. But the selection of glycosidases is still blind because the related mechanisms are not well understood yet. Hence, the animal skin structures and glycoconjugates components, the advances in the methods and mechanisms of removing glycoconjugates related to unhairing and fiber opening-up in leather manufacture, the kinds, compositions, structures and functions of typical glycoconjugates in skin are summarized. Then the approaches to destroy them, possible glycosidases suitable for leather making and their acting sites are analyzed based on the recognition of glycoconjugates in skin and the specificities of glycosidases toward substrates. It is expected to provide useful information for the optimization of glycosidases and the development of new enzymes and the cleaner technologies of unhairing and opening up fiber bundles assisted by glycosidases. Graphical abstract

Traditionally, universally used pelt bating technologies rely on the application of trypsin, neutral and alkaline microbial proteases but suffer from complicated operation, limited bating efficiency and unsatisfactory leather performance. Therefore, devising a new pelt bating approach to achieve high bating efficiency and excellent leather performance has always been wished for by the leather industry. To pursue this goal, years of persistent research work enabled us to develop a novel approach for pelt bating by means of acidic proteases in pickling process. Initially, basic enzymatic characteristics and bating effectiveness of several typical acidic proteases in pelt pickling medium were investigated; then, the bating effectiveness through the quantitative characterization of protease activity of the optimal acidic protease was compared with that of the conventional bating enzyme. The results indicated that all of the selected acidic proteases had good salt-tolerance and exhibited optimum activity at pH 3.0–4.0. The novel pickling-bating method based on microbial origin acidic protease L80A led to an outstanding performance on pelt bating at the dosage of 150 U/mL of collagenolytic activity. The bating effectiveness of acidic protease L80A was comparable to and even better than that of trypsin BEM due to its moderate proteolytic ability. Moreover, the deep and even penetration of acidic protease in the pelt permitted it to produce soft, organoleptically stable and overall better quality crust leather than that of the conventional trypsin bating method. Additionally, pelt bating was performed along with the pickling process without extra inactivation and washing operation, making the bating operation more efficient, economical, and environment friendly. Results had made us to conclude that this cutting-edge acidic proteases based pickling-bating method could be the first step/ way forward to replace the decades-old traditional pelt bating technology.

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Most of the reported bating technologies for wet blue are based on the usage of acidic protease, which takes a long time and needs large enzyme dosage. A thorough understanding of the basic characteristics of typical acidic proteases and the interaction between enzyme proteins and wet blue fibers will help to improve bating technology for wet blue by selecting the suitable proteases. In this paper, the enzymatic characteristics, molecular weight (Mr) and isoelectric point (pI) of several proteases and their bating effectiveness were investigated. The results indicated that there are two main factors which may affect the wet blue bating effectiveness of acidic proteases. First, the common acidic proteases exhibited low activity towards chrome-tanned collagen fiber which lead to inefficient bating effect through normal dosage. Nonetheless, when the dosages of chrome-tanned collagen fiber activity reached up to 50 U/mL, these acidic proteases also can achieve a good bating effect, the caseinolytic activity has been reached up to 1000 U/mL-4000 U/mL. Second, because of the large molecular weight and the charge repulsion between enzyme proteins and wet blue fibers, the enzymatic hydrolysis process, the penetration and distribution of acidic protease proteins, into wet blue is very difficult. Additionally, neutral proteases have more prospects in wet blue bating process due to the higher chrome-tanned collagen fiber activity and less charge repulsion than acidic proteases.