Development of bio-based eggshell waste carrier for R. oryzae lipase immobilization

A challenge for sustainable bio-waste management for circular economy strategies is its conversion into matrices for enzyme immobilization. In this context, R. oryzae lipase (ROL) was immobilized on membrane-free eggshells (MFE), named ROL@MFE. The optimal conditions are an initial lipase concentration of 15,794 IU, a contact time of 30 min, and a stirring speed of 380 rpm, resulting in an immobilization yield of 99.55 %. Freundlich and Langmuir models fit the experimental data better than other models, with correlation coefficients (R²) of 0.997 and 0.993, respectively. Kinetic studies showed that the adsorption of ROL on MFE was best described by the intraparticle diffusion model, which approximates an initial rapid adsorption of proteins. Zeta potential and particle size measurements confirmed a successful immobilization process. Comparison of diffraction patterns showed that ROL is efficiently adsorbed on MFE without perturbing its crystal structure. Electrical conductivity analysis revealed that ROL-MFE interactions are inherently weak ionic bonds. The elemental composition of immobilized ROL, by EDS analysis, showed an increase in carbon and oxygen content compared to MFE alone. The scanning electron microscopy (SEM) image of its surface also showed a rough morphology. In terms of biochemical properties, the immobilized ROL was stable against many factors, indicating its potential for biocatalysis and promoting its future applications.