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Immobilization of enzymes usually improves the recyclability and stability and can sometimes also improve the activity compared to enzymes free in solution. Mesoporous silica is a widely studied material as host for immobilized enzymes because of its large internal surface area and tunable pores. It has previously been shown that the pore size is critical both for the loading capacity and for the enzymatic activity; however, less focus has been given to 20 the influence of the particle size. In this work the effect of particle size and particle morphology on the immobilization of lipase from Mucor miehei and Rhizopus oryzae have been investigated. Three kinds of mesoporous silica, all with 9 nm pores but with varying particle size (1000 nm, 300 nm and 40 nm) have been synthesized and were used as host for the lipases. The two lipases, which have the same molecular size but widely different 25 isoelectric points, were immobilized into the silica particles at varied pH values within the interval 5 to 8. The 300 nm particles were proven to be the most suitable carrier with respect to specific activity for both enzymes. The lipase from Mucor miehei was more than four times as active when immobilized at pH 8 compared to free in solution whereas the difference was less pronounced for the Rhizopus oryzae lipase. 30

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Two enzymes were immobilized in close proximity to each other using enzyme-containing mesoporous nanoparticles and a dendronized polymer–enzyme hybrid structure.

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BackgroundEnzymes display high reactivity and selectivity under natural conditions, but may suffer from decreased efficiency in industrial applications. A strategy to address this limitation is to immobilize the enzyme. Mesoporous silica materials offer unique properties as an immobilization support, such as high surface area and tunable pore size.ResultsThe performance of a commercially available feruloyl esterase, E-FAERU, immobilized on mesoporous silica by physical adsorption was evaluated for its transesterification ability. We optimized the immobilization conditions by varying the support pore size, the immobilization buffer and its pH. Maximum loading and maximum activity were achieved at different pHs (4.0 and 6.0 respectively). Selectivity, shown by the transesterification/hydrolysis products molar ratio, varied more than 3-fold depending on the reaction buffer used and its pH. Under all conditions studied, hydrolysis was the dominant activity of the enzyme. pH and water content had the greatest influence on the enzyme selectivity and activity. Determined kinetic parameters of the enzyme were obtained and showed that Km was not affected by the immobilization but kcat was reduced 10-fold when comparing the free and immobilized enzymes. Thermal and pH stabilities as well as the reusability were investigated. The immobilized biocatalyst retained more than 20% of its activity after ten cycles of transesterification reaction.ConclusionsThese results indicate that this enzyme is more suited for hydrolysis reactions than transesterification despite good reusability. Furthermore, it was found that the immobilization conditions are crucial for optimal enzyme activity as they can alter the enzyme performance.Electronic supplementary materialThe online version of this article (10.1186/s12858-018-0091-y) contains supplementary material, which is available to authorized users.