The use of biotechnology by tanneries has increased in recent years. Enzymes can be applied during different steps of the leather production process: soaking, dehairing, bating, dyeing, degreasing or in effluent and solid waste treatment. This study evaluated the performance of five commercial enzymes in soaking and unhairing/liming by comparing the chemical and coenzymatic processes. Tests were conducted in bench drums to evaluate the action of enzymes during each stage. Concentration, processing time and type of enzyme were varied. Total organic carbon and soluble protein were used to measure the efficiency of the processes. Enzymatic activity assays on collagen, keratin and lipid and scanning electron microscopic (SEM) analyses of hides were used to complement the study. Coenzymatic processes generally showed better results in comparison to chemical processes. The enzymes showed activity on all substrates, and the SEM analyses of the hides showed a clear difference between the chemical and coenzymatic processes.

Olein production from the residue constituents of hide pre-fleshing is carried out through the unit operations of extraction and subsequent fractionation of the fatty material (tallow). The residue was characterized and the content of fatty matter (31.83% by mass) revealed a high potential for its reuse. By the extraction/ digestion of tallow assays were carried out to quantify the effect of factors such as the presence of agitation, temperature and extraction time in terms of the efficiency of the extraction operation and acidity index of the tallows obtained. The oils were characterized according to the acidity index, iodine index, saponification index, water content, volatile matter content and fractions of saturated and unsaturated fatty acids. The oil composition was quantified using gas chromatography.

The enzymatic treatment of hides in tannery processes is a promising technology. However, the reaction kinetics of commercial enzymes available to the leather industry are not fully understood and their activities have been mainly determined with model proteins such as casein as substrate, which are not of direct relevance for cattle hides. Therefore, it is important to determine their activities on collagen and keratin, the main proteins of skin, in order to use these enzymes in leather processing. This work describes the study of five proteases, used commercially in tanneries, to assess their ability to act upon collagen and keratin and to determine their unhairing. Results showed that all commercial enzymes tested had more activity on collagen than on keratin. Unhairing was also tested and four out of the five enzymes tested showed some unhairing activity. Optima of the temperature and pH of the enzymes were very similar for all five enzymes, with maximal activities around 55ºC and pH 9 to 12, respectively.

Chromium used in leather manufacturing can be oxidized from the trivalent to the hexavalent state, causing environmental concerns. In this study, the influence of Cr(III) from tanning, deacidification pH, fatliquors, chrome retanning and vegetable retanning on the formation of Cr(VI) in leather was analyzed by comparing natural and aged samples. In wet-blue leather, even after aging and in fatliquored leathers that did not suffer the aging process, the presence of Cr(VI) was always below the detection limit of 3 mg/kg. Considering the presence of Cr(VI), the supply of chromium during the retanning step had a more significant effect than during the tanning. In the fatliquoring process with sulfites, fish and synthetic fatliquor leather samples contained Cr(VI) when aged, and the highest concentration detected was 26.7 mg/kg. The evaluation of Cr(VI) formation led to recommendations for regulation in the leather industry.