Utilization of a leather industry waste

In the production of leather the main waste that remains after splitting of limed hides before tanning is the lowest layer of the skin together with the underlying fatty tissue (subcutis). It is characterized by a very high water content (up to 870 g kg⁻¹) and a balanced content of protein (40–60 g kg⁻¹ of the dry mass), fat (10–20 g kg⁻¹) of the dry mass) and carbohydrates. The object of this work was to elaborate a method to process this waste into useful products. The treatment proposed involves washing to remove the inorganic salts, separation of fat and extraction of collagen in hot water solution and additional extraction of protein from the insoluble residue after hydrolysis with alkaline proteinase. This results in the isolation of three fractions: fat—cattle tallow (4–12% of the total mass of the initial material), collagen hydrolysate—glue (5–10%) and protein concentrate for fodder (1–3% yield). Up to 95% of the protein in the initial material was extracted. Further purification of the collagen hydrolysate fraction into edible gelatin was achieved. The proposed method is applicable to every leather factory.