Most industrial enzymes are produced by microorganisms, the largest group being photolytic enzymes from bacteria (59%) followed by carbohydrases (20%). Animal enzymes include rennets (for cheese making) and pancreatic protease and lipases; the proteases are used primarily in leather processing. Among the plant enzymes, papain is the largest single industrial product. Industrial enzymes are usually mixtures of different enzymes. Commercial products are standardized with diluents.

Enzymes of fungi and bacteria have a wide variety of industrial applications, including alcoholic beverages, food, detergents, and pharmaceuticals. Table 8-1 lists some of these enzymes, along with their microbial origins and selected uses.

Table 8-1 Microbial Enzymes and Selected Uses

In the production of alcoholic beverages, microbial amylase may be used instead of the enzymes from barley malt to prepare grains for fermentation. Protease can also chillproof beer by degrading the proteins that cause cloudiness in such beverages upon refrigeration.

α-Amylases, together with β-amylases, are present in malt. However, the industrial enzymes are produced from pancreas or from cultures of microorganisms. The various types of α-amylases differ from each other not only in specificity, but also in optimal pH range and stability to heat.

α-Amylases from bacteria are available in either liquid or powder form. These preparations contain varying amounts of other enzymes such as proteinases and β-glucanases. Enzymes concentrates, standardized with sodium chlorides or starch, are marketed as powders with activities of 20 000 to 30 000 SKB/g (pH 5.0). Liquid preparations containing 3 000 to 12 000 SKB/g are stabilized with sodium chloride or glycerol. α-Amylases from Bacillus amyloliquefaciens (分解淀粉芽孢杆菌) has an especially high activity of 50 000 SKB per gram of protein.

Bacterial α-amylases are divided into standard amylases and heat-stable amylases, depending on their stability to heat. Standard bacterial α-amylases from Bacillus subtilis ( 枯草芽孢杆菌) or B. amyloliquefaciens requires temperatures of 70-85 for optimal activity. Heat-stable bacterial α-amylases from, e. g., B. licheniformis (地衣芽孢杆菌), has a temperature optimum between 90 and 105. However, this optimal depends on the pH, the concentration of calcium ions, and the substrate concentration. A typical reaction is carried out on a 30% starch suspension at pH 7.0 and 103-105 for 7-11 min in the presence of 70mg/l of calcium. The enzyme is inactivated by lowering the pH 3.5-4.5 and the temperature to 80-90 for a period of 5-30min.

Bacterial α-amylases are generally stabilized with calcium ions; some types are also activated by sodium chloride. Indeed, amylases freed from calcium by electrodialysis or complex formation are inactive. Heavy metals such as copper, iron, or mercury inhibit enzyme activity. The breakdown of starch yield dextrins. For instance, hydrolysis of potato starch by standard bacterial α-amylases gives the following dextrin spectrum: G1 (glucose) 5%, G2 (maltose) 7%, G3 (maltotriose) 13%, G4 (maltotetraose) 4%, G5 (maltopentaose) 16%, G6 (maltohexaose) 22%, higher dextrins 33%.

α-Amylases from fungi are obtained from Aspergillus niger (黑曲霉) or A. oryzae (米曲霉). They are less resistant to heat than bacterial α-amylases and are inactivated before starch gelatinizes. This is important in the making of bread and biscuits. The following dextrin spectrum is typical of the action of fungal α-amylases: G1 8%, G3 32%, G4 18%, G5 9%, G6 4%, higher dextrins 17%.

β-Amylases, present in grain, soybeans, and sweet potatoes, attacks amylase chains, effecting successive removal of maltose units from the nonreducing ends. In the case of amylopectin, this process stops two to three glucose residues from the α-1,6-branching points (the designation β-amylase refer to the cleaved maltose which has an anomeric carbon atom in the β-configuration). The optimal temperature is 55 at the pH 5.1-5.5. β-Amylase is used in alcohol production and in breweries as a replacement for malt. Obtained in quantity from barley, it is used to saccharify starch in the production of maltose syrup.

Proteases and lipases are used in cleaning animal hides, a necessary step in leather production. Proteases are also used commercially for meat tenderizing, as they are capable of breaking down some of the tough meat protein.

One commercial application of microbial enzymes has been the removal of stains from clothing. Many substances that stain clothes either are made of lipids, proteins, or starches or are held in a fabric by these types of compounds. Certain enzymes, under suitable conditions, can decompose stains or the cementing substances associated with them, thereby helping to clean the soiled fabric. Needless to say, stains can be caused by a large variety of substances, and appropriate enzymes may not be available, or, if available, may not be incorporated into detergent or presoak compounds used in laundering. Thus, it is not surprising that all stains are not removed by commercial products. Moreover, such enzyme-containing products have been associated with the development of allergies.

Microbial enzymes are obtained by process carried out either in shallow pans for optium aeration by diffusion or in tanks where aeration is produced by bubbling air through the growth medium. Usually rich organic wastes from dairy or canning plants are used as the growth medium. When microbial growth is judged to be complete on the basis of an analysis for the desired enzyme, the microorganisms are removed by filtration, leaving the culture filtrate, which can be processed for the desired enzyme.

食品专业英语Lesson 8课文与讲解