Proteolytic extracts of three bromeliaceae species as eco-compatible tools for leather industry

Abstract

In addition to the large quantities of solid waste rich in protein, most tanneries use high proportions of Na2S and CaO during the dehairing step, resulting in effluents of high alkalinity and large amounts of suspended solid, besides the risk of liberating the toxic hydrogen sulphide. The current worldwide legislation on environmental requires tanneries to reduce pollution and to replace conventional processes by greener technologies. Enzymes are a technological tool of interest for industry because are able to achieve a high reaction rate under soft pH, temperature, and pressure conditions, besides a high specificity of reaction, biodegradability, non-toxic nature and non-polluting effluent generation. In leather industry enzymes are principally used in pre-tanning operations (soaking, dehairing, bating, and degreasing) and waste treatment. Particularly, proteases have been chosen as a promising eco-friendly alternative to lime and sodium sulphide dehairing. Extracts rich in cysteine proteases with high proteolytic activity (CU) have been obtained from fruits of Bromeliaceae species: Bromelia balansae (Bb), B. hieronymi (Bh), and Pseudananas macrodontes (Pm). In this work, Bb, Bh, and Pm have been studied for application in leather industry compared with commercial enzyme, focusing in their dehairing properties. Enzymatic activities against representative substrates of skin proteins were spectrophotometrically measured at 25, 35, and 55ºC (Tris-HCl, 0.1 M, pH 8, Cys 20 mM). Keratin Azure (KA), Elastin-Congo Red (E), epidermis substrate (EP), and Hide Powder Azure (HPA) were used as representative substrates of keratin, elastin, epidermis, and collagen, respectively. Ability to dehairing was evaluated by incubating soaked cow skins with different concentrations of extracts at 25ºC and pH 8 during 24 h. Grain surface and cross section of skins were observed by scanning electron microscopy. Extracts were able to degrade representative substrates of skin proteins and when compared to the same CU showed similar activity on collagen and epidermis; however, Bh and Pm were the most actives against keratin, while Bh was the only active against elastin. Extracts showing different proteolytic activity (Bb required 1 CU/ml, Bh 1.5 CU/ml, and Pm 0.5 CU/ml) were able to depilate cow skin after a gentle scraping. Although depilated skins with Bb, Bh, and Pm showed different surface aspects, desirable characteristics of dehairing were observed for all extracts since hair pores did not show residual hair, grain surface were clean and intact, and collagen fiber bundles of dermis were not damaged. In conclusion, results here presented show that proteolytic extracts of Bromeliaceae species are promising eco-compatible tools for leather industry, principally in treatment of their waste and dehairing process.