Production of xylooligosaccharides from xylan catalyzed by endo-1,4-β-D-xylanase-immobilized nanoscale carbon, silica and zirconia matrices

Pros and Cons in Various Immobilization Techniques and Carriers for Enzymes

In recent years, enzyme immobilization technology has been developed, and studies on immobilized enzyme materials have become very prominent. With the immobilization technique, enzymes and compatible carrier materials are combined or enzyme crystals/aggregates are used in a carrier-free fashion, by physical, chemical, or biochemical methods. As a kind of biocatalyst, immobilized enzymes can catalyze certain chemical reactions with high selectivity and high efficiency under relatively mild reaction conditions and eliminate pollution to the environment. Considering the current status and applications of immobilized enzyme technology and materials emerging in the last 5 years, this mini-review introduces the advantages and disadvantages of various enzyme immobilization techniques with carriers as well as the pros and cons of different materials for immobilization. The future prospects of immobilization technology and carrier materials are outlined, aiming to provide a reference for further research and applications of sustainable technology.

Topochemical Design of Cellulose-Based Carriers for Immobilization of Endoxylanase

Xylooligosaccharides (XOSs) gained much attention for their use in food and animal feed, attributed to their prebiotic function. These short-chained carbohydrates can be enzymatically produced from xylan, one of the most prevalent forms of hemicellulose. In this work, endo-1,4-β-xylanase from Thermotoga maritima was immobilized on cellulose-based beads with the goal of producing xylooligosaccharides with degrees of polymerization (DPs) in the range of 4-6 monomeric units. More specifically, the impact of different spacer arms, tethers connecting the enzyme with the particle, on the expressed enzymatic activity and oligosaccharide yield was investigated. After surface functionalization of the cellulose beads, the presence of amines was confirmed with time of flight secondary ion mass spectrometry (TOF-SIMS), and the influence of different spacer arms on xylanase activity was established. Furthermore, XOSs (DPs 2-6) with up to 58.27 mg/g xylan were obtained, which were greatly enriched in longer oligosaccharides. Approximately 80% of these XOSs displayed DPs between 4 and 6. These findings highlight the importance of topochemical engineering of carriers to influence enzyme activity, and the work puts forward an enzymatic system focusing on the production of longer xylooligosaccharides.

Bioconjugation Strategy for Ceramic Membranes Decorated with Candida Antarctica Lipase B-Impact of Immobilization Process on Material Features

A strategy for the bioconjugation of the enzyme Candida antarctica lipase B onto titania ceramic membranes with varied pore sizes (15, 50, 150, and 300 kDa) was successfully performed. The relationship between the membrane morphology, i.e.,the pore size of the ceramic support, and bioconjugation performance was considered. Owing to the dimension of the enzyme (~33 kDa), the morphology of the ceramics allowed (50, 150, and 300 kDa) or did not allow (15 kDa) the entrance of the enzyme molecules into the porous structure. Such a strategy made it possible to better understand the changes in the material (morphology) and physicochemical features (wettability, adhesiveness, and surface charge) of the samples, which were systematically examined. The silane functionalization and enzyme immobilization were accomplished via the covalent route. The samples were characterized after each stage of the modification, which was very informative from the material point of view. As a consequence of the modification, significant changes in the contact angle, roughness, adhesion, and zeta potential were observed. For instance, for the 50 kDa membrane, the contact angle increased from 29.1 ± 1.5° for the pristine sample to 72.3 ± 1.5° after silane attachment; subsequently, it was reduced to 57.2 ± 1.5° after the enzyme immobilization. Finally, the contact angle of the bioconjugated membrane used in the enzymatic process rose to 92.9 ± 1.5°. By roughness (S_q) controlling, the following amendments were noticed: for the pristine 50 kDa membrane, S_q = 1.87 ± 0.21 µm; after silanization, S_q = 2.33 ± 0.30 µm; after enzyme immobilization, S_q = 2.74 ± 0.26 µm; and eventually, after the enzymatic process, S_q = 2.37 ± 0.27 µm. The adhesion work of the 50 kDa samples was equal to 136.41 ± 2.20 mN m⁻¹ (pristine membrane), 94.93 ± 2.00 mN m⁻¹ (with silane), 112.24 ± 1.90 mN m⁻¹ (with silane and enzyme), and finally, 69.12 ± 1.40 mN m⁻¹ (after the enzymatic process). The materials and physicochemical features changed substantially, particularly after the application of the membrane in the enzymatic process. Moreover, the impact of ceramic material morphology on the zeta potential value is here presented for the first time. With an increase in the ceramic support cut-off, the amount of immobilized lipase rose, but the specific productivity was higher for membranes possessing smaller pores, owing to the higher grafting density. For the enzymatic process, two modes of accomplishment were selected, i.e., stirred-tank and cross-flow. The latter method was characterized by a much higher effectiveness, with a resulting productivity equal to 99.7 and 60.3 µmol h⁻¹ for the 300 and 15 kD membranes, respectively.

Highly effective enzymes immobilization on ceramics: Requirements for supports and enzymes

Enzyme immobilization is a well-known method for the improvement of enzyme reusability and stability. To achieve very high effectiveness of the enzyme immobilization, not only does the method of attachment need to be optimized, but the appropriate support must be chosen. The essential necessities addressed to the support applied for enzyme immobilization can be focused on the material features as well as on the stability and resistances in certain conditions. Ceramic membranes and nanoparticles are the most widespread supports for enzyme immobilization. Hence, the immobilization of enzymes on ceramic membrane and nanoparticles are summarized and discussed. The important properties of the supports are particle size, pore structure, active surface area, volume to surface ratio, type and number of reactive available groups, as well as thermal, mechanical, and chemical stability. The modifiers and the crosslinkers are crucial to the enzyme loading amount, the chemical and physical stability, and the reusability and catalytical activity of the immobilized enzymes. Therefore, the chemical and physical methods of modification of ceramic materials are presented. The most popular and used modifiers (e.g. APTES, CPTES, VTES) as well as activating agents (GA, gelatin, EDC and/or NHS) applied to the grafting process are discussed. Moreover, functional groups of enzymes are presented and discussed since they play important roles in the enzyme immobilization via covalent bonding. The enhanced physical, chemical, and catalytical properties of immobilized enzymes are discussed revealing the positive balance between the effectiveness of the immobilization process, preservation of high enzyme activity, its good stability, and relatively low cost.