Large scale applications of immobilized enzymes call for sustainable and inexpensive solutions: rice husks as renewable alternatives to fossil-based organic resins

Abstract

Despite the extensive efforts of scientific community towards the development of a vast variety of immobilization methods, there is a limited number of immobilized biocatalysts used at industrial scale. Most often, cost issues prevent the transfer of methodologies to large scale but more recently also sustainability criteria are becoming increasingly relevant, so that petroleum based carriers for enzyme immobilization appear unsuitable for responding to new challenges of green and renewable chemistry. Here we report, for the first time, a preliminary overview of the potential of rice husk as carrier 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 husk, along with its virtual unlimited availability worldwide, make this inexpensive natural matrix a promising candidate for replacing organic fossil-based carriers for enzyme immobilization.Computational construction of 3D models and surface analysis. Protein structures were visualized and recorded using the PyMOL software. The 3D-structures used for the hydrophobicity comparisons were retrieved from the PDB with the codes 1TCA for CaLB, 5DPF for Thermolysin and 4EQV for Invertase

Nature Inspired Solutions for Polymers: Will Cutinase Enzymes Make Polyesters and Polyamides Greener?

“…The porosity of carriers seems to play a negligible role in the process design, rather, porosity might induce the risk of undesired occlusion by substrates and products, thus limiting the efficiency of the enzyme. This assumption is also supported by recent data obtained in polycondensation catalyzed by hydrolases immobilized on rice husk [59,66]. Although the enzymes (CaLB and Thc_cut1) were immobilized only on the surface either through adsorption-crosslinking or covalent bonding, the polyester synthesis proceeded with comparable rates and conversion as in the case of the macroporous methacrylic resins.…”

“…Processes catalyzed by enzymes and whole cells will, in the coming years, be major players for global sustainability. In this sense, the industrial need of robust and heterogeneous biocatalysts to be recovered and reused makes immobilization procedures a key step of practical relevance; it is noteworthy that, also in the perspective of substituting petrol-based carriers that are currently on the market, immobilization technologies recently developed with cheap, stable, and renewable rice husks are of particular interest [66].…”

Functionalization of Enzymatically Synthesized Rigid Poly(itaconate)s via Post‐Polymerization Aza‐Michael Addition of Primary Amines

“…At the end of the activity assay, it was verified that there was no enzyme leaching from the support. [27] The recyclability of CaLB covalently immobilized on rice husk has been demonstrated in a previous study [21] and it is the consequence of a remarkable stiffness of this natural composite material because of the high silica and the lignin content. [21]…”

“…[8b] Therefore, 50% w/w of three different low-loaded formulations of covalently immobilized CaLB were tested (see experimental) on a scale ranging from 2 to 16 g. Besides using two preparations immobilized on epoxy methacrylic carriers (specific activities of 526 and 338 U/g dry respectively) we also employed activated rice husk, a renewable and inex-pensive support (specific activity of the formulation = 309 U/g dry ). [21,26,27] The efficiency of the polycondensation reactions was confirmed by GPC, 1 H-NMR and ESI-MS spectra (see SI, Figures S7-10 and S17-20). The longest oligomers were obtained using the rice husk carrier (M n = 1600 g mol À 1 and M w = 2900 g mol À 1 ; Đ = 1.76), thus indicating the possibility to mitigate the negative environmental and economic impact deriving from the use of large amounts of fossil based carriers.…”

“…[9c,20] The use of a covalently immobilized CaLB prevented the contamination of the product (see experimental section) by the enzyme while enabling and efficient recycling of the biocatalyst. [8,21,22] As discussed by Ansorge-Schumacher and Thum, the above mentioned factors, along with the mechanical integrity of the biocatalyst, are of primary importance for the viability of biocatalytic industrial processes, especially in the cosmetic sector. [23] Actually, despite the high viscosity of the reaction mixture, the integrity of the biocatalyst and the efficiency of the mass transfer were assured by the application of the thinfilm technology, which was previously described.…”