For energy production, the world depends to a large extent on non-renewable fossil fuels, mainly in the transport sector1. Therefore, the use of a renewable and sustainable energy source, such as lignocellulosic biomass (sugarcane bagasse and straw, corn stover, among others), it becomes a viable alternative in the second-generation (2G) bioethanol production. The chemical composition of lignocellulosic residues mainly contains cellulose and hemicellulose, which by hydrolysis, produce mostly glucose and xylose, respectively. These monosaccharides can be converted to 2G bioethanol through the alcoholic fermentation carried out by yeasts2. However, the main yeast used in ethanol production, Saccharomyces cerevisiae, cannot naturally metabolize xylose. For this reason, the use of new technological routes, such as enzymatic catalysis, becomes an alternative to increase the 2G bioethanol production. In this context, the enzyme xylose isomerase (XI) that catalyzes the interconversion of xylose to xylulose, a product easily fermented by S. cerevisiae, was applied as a heterogeneous biocatalyst, through its immobilization by crosslinking with the glutaraldehyde in Fe3O4 magnetic nanoparticles (MNPs). Fe3O4 MNPs were synthesized by a coprecipitation method3 in the presence of the 1-methyl-3-octadecyl-imidazolium bromide ionic liquid, previously
synthesized and characterized, in the chloroform and water mixture. In this way, it was possible to obtain nanoparticles of controlled size, between 2 and 8 nm, which were characterized by transmission electron microscopy (TEM). Some parameters are considered important in the enzyme-support immobilization reaction, because during this process there may be a significant loss of its catalytic activity. For this reason, the immobilization parameters were minutely optimized
using 2^6-3 fractional factorial design, which resulted in six independent variables. The response (dependent variable) was the quantification of the reaction product (D-xylulose), after immobilized XI catalytic activity, using a method developed by liquid chromatography coupled to mass spectrometry (LC-MS). The independent variables were: Fe3O4 MNPs, glutaraldehyde, enzyme, pH, temperature, and time. Among them, only the pH showed a greater influence on the immobilization process. The heterogeneous biocatalyst with the highest conversion of D-xylulose obtained from the factorial design was 65%, while the free XI converted 35%. In conclusion, the use of XI immobilized on Fe3O4 MNPs showed a catalytic activation when compared to the use of the free enzyme in solution.
 

References:
1. Zabed, H., Sahu, J. N., Boyce, A. N. & Faruq, G. Fuel ethanol production from lignocellulosic biomass: An overview on feedstocks and technological approaches. Renew. Sustain. Energy Rev. 66, 751–774 (2016).
2. Victor, B., Ali, M. & Indati, S. An overview of integration opportunities for sustainable bioethanol production from first- and second-generation sugar-based feedstocks. J. Clean. Prod. 245, 118857 (2020).
3. Laurent, S. et al. Erratum: Magnetic iron oxide nanoparticles: Synthesis, stabilization, vectorization, physicochemical characterizations, and biological applications. Chem. Rev. 110, 2574 (2010).