Enzymatic Hydrolysis of Chromium Tanned Leather Wastes, Amino Acid Composition Analysis and Chemical Characterization of Hydrolysate

Abstract

The disposal of leather wastes poses many challenges and is a major threat to the environment in many countries across the world. Large amounts of wastes from the tanneries including: shavings, trimmings, sludge and untreated waste waters are disposed to the environment and pose a threat to the environment and humans. Solid wastes in particular are non-biodegradable and therefore remain in the environment for a long period of time. The major tanning agent is chromium, a clear indication that the solid wastes and even the liquid waste expose the environment to significant amount of chromium. In this study enzymes extracted from Lake Bogoria, an extremophile environment were used to hydrolyze leather trimmings to generate valuable products and consequently reduce the effect of solid waste disposal and chromium discharged to the environment. Different parameters such as pH, temperature and time were optimized for enzymatic hydrolysis. Characterization of the hydrolysate was done using FTIR and HPLC and the heavy metals were analyzed using Inductively Coupled Plasma mass spectroscopy (ICPMS). The enzyme was able to hydrolyze the trimmings under optimum conditions. The optimum conditions for hydrolysis were pH of 12 and a temperature of 75oC. FTIR analysis of the samples showed peaks at 3290.56 cm -1 and 3334.92 cm -1 indicating the presence of amide bands. The HPLC analysis indicated the presence of 16 and 15 amino acids in the freeze dried and dry filtrate respectively. Further, glycine was the most abundant amino acid comprising 37.83% and 43.36% mole fraction in the freeze dried and dry filtrate samples respectively. Glycine also indicated large percentage by mass in both samples, 25.17% in freeze dried sample and 29.23% by weight in the dry filtrate. Both Histidine and Tryptophan were absent in both samples. The element content of the samples was analyzed using Inductively Coupled Plasma mass spectroscopy (ICP-MS) and it indicated the presence of Cr and S, in addition to several other elements. The dry filtrate showed higher element content filtrate than in the freeze dried samples. This study shows that gelatin can be obtained from the leather wastes and the enzyme hydrolysis process can be achieved within 21 hours, under the optimum conditions established.