Rice Husk as an Inexpensive Renewable Immobilization Carrier for Biocatalysts Employed in the Food, Cosmetic and Polymer Sectors

Abstract

The high cost and environmental impact of fossil-based organic carriers represent a critical bottleneck to their use in large-scale industrial processes. The present study demonstrates the applicability of rice husk as inexpensive renewable carrier for the immobilization of enzymes applicable sectors where the covalent anchorage of the protein is a pre-requisite for preventing protein contamination while assuring the recyclability. Rice husk was oxidized and then functionalized with a di-amino spacer. The morphological characterization shed light on the properties that affect the functionalization processes. Lipase B from Candida antarctica (CaLB) and two commercial asparaginases were immobilized covalently achieving higher immobilization yield than previously reported. All enzymes were immobilized also on commercial epoxy methacrylic resins and the CaLB immobilized on rice husk demonstrated a higher efficiency in the solvent-free polycondensation of dimethylitaconate. CaLB on rice husk appears particularly suitable for applications in highly viscous processes because of the unusual combination of its low density and remarkable mechanical robustness. In the case of the two asparaginases, the biocatalyst immobilized on rice husk performed in aqueous solution at least as efficiently as the enzyme immobilized on methacrylic resins, although the rice husk loaded a lower amount of protein.

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

“…[26] The best formulation of CaLB immobilized on methacrylic resins gave products with M n = 1100 g mol À 1 and Mw = 1800 g mol À 1 (Đ = 1.61). As previously reported, [27] the low density (0.4 g mL À 1 ) of rice husk allows the distribution of the enzyme on a wider surface of carrier as compared to the methacrylic resin (density~1.1 g mL À 1 ). Hence, the volume of the rice husk carrier was at least double on a weight basis as compared to methacrylic resins and that improves the accessibility of the enzyme.…”

“…Our previous experimental and docking studies indicate that the elongation of poly(itaconate)s occurs with more difficulty when BDO is used as co‐monomer . 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 inexpensive support (specific activity of the formulation=309 U/g dry ) …”

“…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.…”

“…More than 98% of protein was immobilized and it was verified that there was no enzyme leaching from the support using a method previously reported. [27] CaLB Immobilized Covalently on Functionalized Rice Husk (RH-CaLB) 10.000 units of CaLB (tributyrin Units) were loaded on 1 g of dry, oxidised rice husk and functionalized with HMDA according to the previously reported protocol. [41] 72% of the protein was loaded on the carrier after 48 h of reaction at 25°C.…”