Adding Value to Non-Food Grade Leather By-Products

Per raw animal hide brought into the leather manufacturing process, only around 25% wet weight ends up as final usable product. The remaining 75% of solid wastes consists of skin trimmings, fleshings, shavings, buffing dust and keratin waste. Scottish Leather Group believes there is more value to be added to these waste materials, in particular to greaves, which are a residue of the limed fleshings. This by-product is currently disposed of to anaerobic digestion, but due to the high protein content, it is thought the protein could be extracted and purified from greaves, to yield a higher value end-marketplace.
The first stage of this project was to develop a full-scale extraction process for the protein fraction of greaves. Once this protein was extracted, it then had to be purified and dried, in a way that would preserve any remaining functionality. The purified protein was then tested for a range of functionalities, including foaming, emulsifying, gelling, film- formation and water retention properties. A second enzymatic extraction was then used for the remaining solids. From initial lab-scale work, a partially hydrolysed functional protein product of 90% purity could be attained via a combination of chemical and thermal treatment of the greaves. This functional protein accounts for ~50% of the total dry weight of greaves, with the remaining 50% accounting for another non-functional protein filler. The results of this work confirm there is significant high-value potential present within the greaves, which can be easily liberated through a process of gentle chemical and thermal treatment. End markets for the functional protein are likely to be the cosmetic or medical markets; and for the non-functional protein, ideally the fertiliser or leather chemical markets. Further work on the process at pilot-scale will contribute towards process validation, and provide Scottish Leather Group with sufficient product for customer testing.