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Rice husk is an underexploited, low density and highly robust composite material, massively available from rice processing. Here we report two new procedures for the formulation of immobilized lipases applicable in fats and oils transformations. The enzymes were covalently anchored on aldehyde groups introduced on rice husk by laccase-catalysed oxidation of the cellulose component. The method avoids the use of toxic glutaraldehyde while allows for the application and recycling of the biocatalysts in aqueous media. The second method used a fluidized bed granulator for the coating of the particles of rice husk (200–400 μm) in the presence of water-soluble binders. The formulations are mechanically stable and suitable for applications in different hydrophobic media. Both methods allow for the recovery and reuse of the rice husk at the end of the life cycle of the biocatalysts.

Despite the extensive efforts of the scientific community towards the development of a vast variety of immobilization methods, there is a limited number of immobilized biocatalysts used at an industrial scale. Most often, cost issues prevent the transfer of methodologies to large scale but more recently sustainability criteria are also becoming increasingly relevant, so that petroleum based carriers for enzyme immobilization appear unsuitable for responding to the new challenges of green and renewable chemistry. Here we report, for the first time, a preliminary overview of the potential of rice husks as carriers to be employed for both physical and covalent immobilization of enzymes. The data indicate that the chemical versatility of this lignocellulosic biomass, containing also silica, opens wide scenarios for optimizing different immobilization procedures requiring minimal pre-treatments and applicable to various enzymes and process conditions. The mechanical and chemical robustness of rice husks, along with their virtually unlimited availability worldwide, make this inexpensive natural matrix a promising candidate for replacing organic fossil-based carriers for enzyme immobilization.

The present study addresses comprehensively the problem of producing polyesters through sustainable processes while using fully renewable raw materials and biocatalysts. Polycondensation of bio-based dimethyl adipate with different diols was catalyzed by cutinase 1 from Thermobifida cellulosilytica (Thc_cut1) under solvent free and thin-film conditions. The biocatalyst was immobilized efficiently on a fully renewable cheap carrier based on milled rice husk. A multivariate factorial design demonstrated that Thc_cut1 is less sensitive to the presence of water in the system and it works efficiently under milder conditions (50 °C; 535 mbar) when compared to lipase B from Candida antarctica (CaLB), thus enabling energy savings. Experimental and computational investigations of cutinase 1 from Thermobifida cellulosilytica (Thc_cut1) disclosed structural and functional features that make this serine-hydrolase efficient in polycondensation reactions. Bioinformatic analysis performed with the BioGPS tool pointed out functional similarities with CaLB and provided guidelines for future engineering studies aiming, for instance, at introducing different promiscuous activities in the Thc_cut1 scaffold. The results set robust premises for a full exploitation of enzymes in environmentally and economically sustainable enzymatic polycondensation reactions.