Valorization of Soda Lignin from Wheat Straw Solid-State Fermentation: Production of Oleogels

This work describes the solid-state fermentation (SSF) of wheat straw with Streptomyces sp. MDG147 and further soda-pulping process to obtain wheat straw soda lignins (WSLs). Subsequently, these WSLs were NCO-functionalized with 1,6-hexamethylene diisocyanate and then dispersed in castor oil to achieve stable oleogels. The WSLs were characterized using standard analytical methods, gel permeation chromatography, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Rheological properties of oleogels were determined by means of small-amplitude oscillatory shear and viscous flow measurements. The enzymatic profile and production of lignin-carbohydrate complexes were recorded along the growth time of Streptomyces, whose life cycle was achieved after 7 days. NCO-functionalized WSL was able to chemically interact with castor oil via urethane bonding, providing oleogels with suitable rheological characteristics. Linear viscoelastic functions and viscosity values of oleogels were higher when wheat straw was submitted to SSF using Streptomyces, turning out in stronger oleogels.