Eco-Friendly Oleogels from Functionalized Kraft Lignin with Laccase SilA from Streptomyces ipomoeae: An Opportunity to Replace Commercial Lubricants

This work demonstrates the usefulness of SilA laccase from Streptomyces ipomoeae to functionalize Kraft lignin to be used as a thickener in the preparation of biodegradable oleogels for lubricating purposes. First, conditions for the enzymatic reaction were optimized by determining the polymerization degree of lignin along the incubation time. Next, using rheological characteristics as a response function, the Kraft lignin amount and incubation time were optimized to get the best characteristics of functionalized Kraft lignin to be used as a thickener in castor oil oleogels. In both cases, response surface methodology (RSM) with a factorial design 2(3) was applied. The results obtained demonstrated that Kraft lignin was oxidized by recombinant laccase from S. ipomoeae (SilA) increasing its reactivity and, as consequence, the molecular weight average. It was estimated that the highest polymerization occurred with a Kraft lignin concentration of 1.25 g/L and an incubation time of 24.0 min. Moreover, the maximum values of the "plateau modulus" for the oleogels within the limits of the studied region were reached with 66.6 g/L of Kraft lignin and a reaction time of 1.98 h. In conclusion, eco-friendly oleogels obtained in this work fulfil the industrial requirements concerning their rheological properties to be considered as an efficient and biodegradable alternative to traditional lubricants containing lithium as the thickener.