Biochemical and Physical Characterization of Immobilized Candida rugosa Lipase on Metal Oxide Hybrid Support

Combined cross-linked enzyme aggregates of cyclodextrin glucanotransferase and maltogenic amylase from Bacillus lehensis G1 for maltooligosaccharides synthesis

Maltooligosaccharides (MOS) are functional oligosaccharides that can be synthesized through enzymatic cascade reaction between cyclodextrin glucanotransferase (CGTase) and maltogenic amylase (Mag1) from Bacillus lehensis G1. To address the problems of low operational stability and non-reusability of free enzymes, both enzymes were co-immobilized as combined cross-linked enzyme aggregates (Combi-CLEAs-CM) with incorporation of bovine serum albumin (BSA) and Tween 80 (Combi-CLEAs-CM-add). Combi-CLEAs-CM and Combi-CLEAs-CM-add showed activity recoveries of 54.12 % and 69.44 %, respectively after optimization. Combi-CLEAs-CM-add showed higher thermal stability at higher temperatures (40 °C) with longer half-life (46.20 min) as compared to those of free enzymes (36.67 min) and Combi-CLEAs-CM (41.51 min). Both combi-CLEAs also exhibited higher pH stability over pH 5 to pH 9, and displayed excellent reusability with >50 % of initial activity retained after four cycles. The reduction in K_m value of about 22.80 % and 1.76-fold increase in starch hydrolysis in comparison to Combi-CLEAs-CM attested the improvement of enzyme-substrate interaction by Tween 80 and pores formation by BSA in Combi-CLEAs-CM-add. The improved product specificity of Combi-CLEAs-CM-add also produced the highest yield of MOS (492 mg/g) after 3 h. Therefore, Combi-CLEAs-CM-add with ease of preparation, excellent reusability and high operational stability is believed to be highly efficacious biocatalyst for MOS production.

A Hands-on Guide to the Synthesis of High-Purity and High-Surface-Area Magnesium Oxide

In this study, magnesium nitrate, chloride or sulphate were used in the synthesis of Mg(OH)2, the precursor of MgO. It was found that the counter ion strongly influences the purity of the Mg(OH)2, as well as the specific surface area of the obtained MgO. The latter is also strongly influenced by the calcination temperature. The choice of the precipitating agent can lead to the introduction of K+ or Na+ ions and hence NH3 (aq) is the best choice. A multistep precipitation procedure of Mg(OH)2 was proposed to lower the concentration of typical impurities (Fe, Ni and Mn) found in commercial p.a. purity Mg(NO3)2. The effect of the number of portions of water used for washing of Mg(OH)2 on the purity of the final product has also been investigated in detail. The stages of formation of grains of Mg(OH)2 and their subsequent thermal decomposition was described together with determination of the introduction of new impurities into the material. Large scale (1500 g) preparation of Mg(OH)2 with an improved purity was performed and described. Therefore, this study explains what measures should be taken to obtain pure magnesia catalysts and is a valuable resource for catalytic research in which magnesia is used.