Solid-State Fermentation with Streptomyces as an Ecofriendly Routeto Tune Lignin Properties and Its Use as a Binder in Adhesive Formulation

The herein work analyzes the compositional and structural modification of extracted lignins from both barley and wheat straws biologically pretreated with Streptomyces by solid-state fermentation with two different strains, MDG147 and MDG301. The results showed that the MDG301 strain promoted major ligninsolubilization, especially for wheat straw and alkaline extraction, and simultaneously exhibited a higher hydrolytic enzymatic profile than MDG147. Furthermore, the substrates were submitted to soda pulping, and the chemical composition and structural characteristics of the extracted soda-lignins were analyzed by analytical standard methods, Fourier transform infrared spectroscopy,thermogravimetric analysis, and nuclear magnetic resonance. Generally, soda-lignins showed high purity, with the remaining carbohydrate content in agreement with enzymatic patterns. Moreover, Streptomyces strains produced structural modifications, including a major degradation of beta-alkyl-aryl ether and C-C linkages of soda-lignins, as well as an enrichment of syringyl units. Furthermore, these modifications also increased the hydroxyl group content, increasing entanglement possibilities and H-bonding. The obtained soda-lignins were focused on as binders for the adhesive formulation, showing excellent adhesion results. Those adhesives based on lignin coming from barley straw exhibited the best performance in shear strength tests, whereas those extracted from wheat straw provided the maximum values in peeling essays.