Wool keratin total solubilisation for recovery and reintegration - An ecological approach

Organic waste is a valuable raw material with potential for replacing synthetic products of petroleum origin in a more sustainable economy. Such a material is unmarketable wool, which is a growing resource in many countries and has recently concerned authorities because of the low degree of biodegradation of keratin and the potential for long-term environmental pollution. At the same time keratin represents a smart protein with high compatibility for cell growth and with high sulphur content which can be used for plant treatment in a circular economy. In this respect the aim of this research was to develop a facile and versatile method for total solubilisation of keratin from unmarketable wool which was experimented at pilot level with high potential for reintegration in ecological agriculture. The original investigations indicated that different properties can be tailored by alkaline or alkaline-enzymatic hydrolysis of wool waste with preservation of 9.2–19.2% of cystine sulphur as compared to raw wool. The measurement of particle sizes, zeta potential and contact angle demonstrates that the keratin peptides are able to associate and self assemble with influence on particle size, stability and hydrophilic properties. FTIR-ATR, CP/MAS ¹³C-NMR and Cryo-STEM-EDX analyses highlighted specific chemical modification of keratin polypeptide with cleavage of disulphide bonds and dehydroalanine generation only in alkaline hydrolysates and with more alkyl species and oxidized sulphur in enzymatic hydrolysates. The results indicated that different compositions of keratin hydrolysates can be modulated through alkaline and enzymatic hydrolysis with release of metabolism precursors for plant growth which can be alternatives to the use of synthetic products. Preliminary tests on foliar fertilization of wheat plants opened the path for large scale application of keratin hydrolysate solubilised with zero waste from wool by-products, in a more ecological agriculture.