Methods for catalyzing biochemical reaction and increasing cell number
Immobilized: English name: immobilized;immobilization; Immobilization means usingPhysicsOr chemically make the enzymeInsoluble derivativeOr make the cell into a form that is not easy to lose from the carrier, and make it into a bioreactor to catalyzebiochemical reaction 、CellsProliferation of quantity, etc.
1. It includesImmobilized enzymeTechnology andImmobilized cell technology。Immobilized cellsCarriers can be mainly divided into two categories, one is inorganic carrier, such as diatomite, activated carbon, etc;The other is organic carrier, which can be divided into two types. One is natural polymer gel carrier, such as agar, carrageenan and calcium alginate. They are non-toxic, good in mass transfer, but low in strength, and easily biodegradable under anaerobic conditions.The other is organic synthesisPolymer gelCarriers, such as acrylamide ammonium (ACRM) gel, polyvinyl alcohol (PVA) gel, etc., generally have good strength, but poor mass transfer performance, which affects cell activity after embedding.
Compared with natural free cells, the advantages of the immobilized cell process can be shown as follows: the cell immobilized carrier provides sufficient space for microbial growth;GuaranteedBioreactorThe higher cell concentration in the cell makes the reaction speed faster, thus having higher productivitySince the cells are fixed by the carrier, there is no loss, and the dilution rate of continuous reaction is greatly improved;In the process of separation and purification, it is very easy to separate the bacterial cells from the fermentation brothSince the immobilized cells can be reused for many times for a long time, it simplifies the complicated operation of the free cell process that requires continuous cultivation of bacteria, and prevents the waste of nutrient matrix.
(1) The immobilization process is simple, the reaction is mild, and it is easy to be made into various shapes. It can be immobilized at normal temperature and pressure;
(2) Easy access to raw materials and low cost;
(3) The carrier is inert to cells and harmless to microorganisms during and after immobilization;
(4) The fixed carrier has good light transmittance, and the diffusion resistance of reaction substrate and product is small;
(5) The density of immobilized cells per unit volume is high;
(7) It is resistant to microbial decomposition and can withstand the rupture caused by biological proliferation;
(8) The cells inside the carrier leak less, and the cells outside are difficult to enter;
Generally speaking, the commonly used microbial immobilization methods can be roughly divided into four categories: adsorption method, covalent combination method, cross-linking method and embedding method:
1. Adsorption method: many cells have the ability to adsorb onto the surface of solid substances or other cell surfaces. The adsorption method can be divided into physical adsorption method and ion adsorption method. The former uses silica gel, activated carbonPorous glassAdsorbents such as zeolite, quartz sand and cellulose adsorb cells onto the surface to immobilize them.The latter is based on the fact that the cell can be fixed to theIon exchangerOn.The production of acetic acid in an immobilized reactor filled with sawdust adsorption cells is one of the earliest immobilized cell processes.The adsorption process has simple technical requirements, low cost, renewable and reusable carrier, small steric hindrance, mild reaction process, but poor firmness. When the external environment mutates, it is easy to cause microorganisms (enzymes) to fall off from the carrier.Binding amount of immobilized cells (enzymes) andbiological activityThe type of carrier has a greater impact.In such systems, there is no barrier between the cells and the solution, so it cannot be used in situations where the outlet feed solution is required to contain no free cells.
2. Covalent combination method:cell surfaceA method for cell immobilization by forming chemical covalent bond between the upper functional group and the reaction group on the surface of the solid support.The covalent combination method has a strong binding force with the solid carrier. However, because of the intense reaction and complex operation during the fixation process, the activity of microorganisms is greatly inhibited, and the general application is poor.
3 Cross linking method: The cross linking method is similar to the covalent binding method, which uses the intermolecular interaction between two or more functional groups on the surface of the carrier and the cell to immobilize the cell, but the carrier used in the cross linking method is water-insoluble, and the cross-linking agent is mostly glutaraldehyde, diazobenzidine, etc.The cells fixed by cross-linking method are firmly connected with the carrier and have high stability. However, the biochemical reaction in the cross-linking process is complex and intense, which inhibits the activity of microorganisms and has a narrow scope of application.
Embedding method: embedding method is the most commonly used method for cell immobilization.According to the structure of embedding coefficient, it can be divided into gel embedding and microencapsulation methods, that is, cells are wrapped in the micro grid of gel or ultrafiltration membrane of semi permeable membrane polymer. This method has low cost, simple operation, little impact on cell activity, and the strength of the immobilized cell spheres is high.However, the mass transfer resistance is large.
Comprehensive performance
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The embedding method has good comprehensive performance, high catalytic activity retention and viability, and flexible application in reaction engineering (including reactor design, operational stability, etc.). Therefore, the embedding method becomes the whole immobilizationBiocatalystThe most widely used immobilization method in technology;However, the entrapment method has a large diffusion resistance, which limits the catalytic activity of cells and is more suitable for the reaction of small molecular substrates with products.
