Enzymes unit operations

Within the chemical industry, micro-organisms and enzymes are often used as catalysts. It is possible for a unit operation in an essentially chemical production process to be a biochemically catalysed step giving rise to a mixed chemical/biochemical production process. The products of these reactions include organic chemicals, solvents, polymers, pharmaceuticals, and purfumes. Mixed chemical/biochemical production processes are continuously innovated and optimised, mainly for economical reasons. 

At the start of optimization of the reaction system, suitable values for pH and temperature have to be chosen as a function of the properties of the reactants and enzymes. Fortunately, most enzyme reactions operate in a narrow band with respect to pH value (7-10) and temperature (30-50 °C). The initial substrate concentration and, in the case of two-substrate reactions, the stoichiometric ratio of the two reactants, have to be selected. The selected enzyme concentration influences both the achievable space-time-yield as well as the selectivity in the case of undesired parallel or consecutive side reactions. In the case of multi-enzyme systems, the optimal activity ratio has to be found. The activity and stability of all the enzymes involved have to be known as a function of the reaction conditions, before the kinetic measurements are made. Enzyme stability is an important aspect of biocatalytic processes and should be expressed preferably as an enzyme unit consumption number, with the dimension unit of activity per mass of product (such as mole, lb, or kg). In multi-enzyme systems the stability of all the enzymes has to be optimized so that an optimal reaction rate and space-time-yield result. 

The principles and equipment discussed below are mostly focused on proteins and enzymes. Several other products, such as small molecules, metabolites, vitamins, and acids can require more specialized methods. However, many of the unit operations described here are also used in the recovery of these latter compounds. 

Common unit operations of food processing are reported to have only minor effects on the carotenoids (Borenstein and Bunnell 1967). The carotenoid-protein complexes are generally more stable than the free carotenoids. Because carotenoids are highly unsaturated, oxygen and light are major factors in their breakdown. Blanching destroys enzymes that cause carotenoid destruction. Carotenoids in frozen or heat-sterilized foods are quite stable. The stability of carotenoids in dehydrated foods is poor, unless the food is packaged in inert gas. A notable exception is dried apricots, which keep their color well. Dehydrated carrots fade rapidly. 

Another aspect of heating soybeans in particular is the impact on the phospholipase enzyme. The phospholipase enzyme is activated at approximately 55°C and remains activated up to approximately 100°C. In this temperature range, and with sufficient exposed surface area and time, the phospholipase enzyme modifies a portion of the phospatides in the oil fraction by splitting off the non-fatty acid moiety (16). The resultant calcium and magnesium salts of phosphatidic acids that are formed tend to be more oil-soluble than water-soluble, thereby converting phospatides from a hydratable form to a nonhydratable form (16). This has a resultant impact on the quantities of acid, caustic and silica needed to reduce the phosphorus content of the soybean oil in the downstream degumming and refining unit operations. 

Proteolytic enzymes are released to the medium because of cell death, mechanical stress, or induced cell lysis. Their presence is expected during fermentation and initial downstream unit operations. Most enzymes of the vacuoles and... 

In the following, results from our work with these processes in Novo s pilot plant for Enzyme Application will be presented. The results demonstrate that the functional properties of some of the protein products obtained were improved to such an extent that the membrane processes may become very important in the modern protein technology. Owing to the interesting preliminary results obtained regarding functional properties, less attention has been paid to a thorough investigation of the unit operations as such. 

The key part of the reactor is a nanofiltration membrane unit (a), which allows the permeation of small molecules but not macromolecules such as enzymes. In operation, the reactor is initially charged with d-LDH and FDH before the start of the reaction. An aqueous mixture, which consists of 6, ammonium formate, and a catalytic amount of NAD, is then continuously fed into the reactor by a peristaltic pump (b). After passing a check valve (c), the substrate solution is mixed with enzymes inside the reactor by a circulation pump (d). The product is collected continuously as an effluent from the filtration membrane unit. In this fashion, both enzymes are retained inside the reactor by the membrane leading to high turnover. 

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