Practical Applications Of Industrial Microbiology

Industrial microbiology is a branch of applied microbiology in which microorganisms are used in different industrial processes. Because of their putrefactive, fermentative, and synthesizing abilities, microorganisms have attained a useful place in many industrial processes, including the manufacture or processing of food, clothing and drugs. Microbial enzymes are used in the manufacture of leather and likewise, in the manufacture of linen. Moreover, these enzymes are used in improving or enhancing the flavor of coffee, cocoa, vanilla pods and tobacco. There are a number of different fermented foods like cheeses that are acquired by microbial fermentation.

Production of beer and wine

In alcoholic beverages, sugars are converted into alcohol by fermentation C6H12O6 2CO2 + 2C2H5OH

Wine is the product of alcoholic fermentation of grape juices. Grapes are harvested when they have about 22% sugar content. Then these are transported to vinery where they are steamed and crushed by machines. Because of yeast on their surface, fermentation in grapes will begin immediately. However, some microorganisms in grape fruits are undesirable so sulphur dioxide is added to kill these microorganisms. The nature of fermentation will depend on the type of wine desired. While color is derived from grape skins so, white wine can be prepared from white grapes. For the heavier red wines fermentation is allowed to proceed for 3-5 days before juice is separated from the skins of red grapes. When the major fermentation is complete, the wine will contain 12-14% alcohol. It is aged for various periods during which proteins precipitate, esters are formed and wine loses much of its harsh flavor. Other red wines such as burgundies and clarets maybe aged from 5-40 years before they reach their peak of flavors. Dessert wine such as port or muscatel wine are made by the halting fermentation at the end of second day and brandy which is made by distilling wine is then added to bring the alcohol content about 20 %.

Beer is made from barely and other cereals and preparation of beer is much different from the preparation of wine. Because these starting substances contain more fermentable material, this is accomplished by using the enzymes formed in barely itself when it germinates itself. Major steps in beer production are:

1. Barely is allowed to germinate by soaking in water. The germinated barley is rich in enzymes that hydrolyze starch in simple sugars, after drying, this is termed as malt.
2. Malt is dissolved in water and other ground cereals maybe added at this time. The temperature is maintained at 65-70oC to facilitate enzymatic hydrolysis of starch.
3. After filtering, hops are added and liquid called wort is boiled for 1-2 hours to inactivate enzymes, precipitate some proteins and extract the flavor of hops.
4. The wort is again filtered and pumped to fermentation tanks where it is inoculated with yeast (S. carlsbergensis)
5. After fermentation for 8-14 days at 4-6oC, it is aged for several weeks to permit proteins, yeast and resins to precipitate before it is filtered and bottled.

Moreover, a microbiologist should know the difference between regular beer and that which advertising agencies called light beer. The starch present in barely consist of polymers of glucose that are linked to each other by α1-4 linkage and α1-6 linkage. The hydrolytic enzymes in malt can hydrolyze only α1-4 linkages leaving α1-6 linkages. These residual glucose polymers are called as limit dextrans. Because yeast cannot metabolize them, they remain in final beer. Limit dextrans account for 22% of total starch in regular beer, when metabolize by body, they add to the total calories in the beer. If however, before fermenting the wort, mould enzymes that will break these, α1-6 linkages are added, all glucose will be fermented reducing the number of calories to yield light beer.

Production of distilled beverages

Natural fermentation of carbohydrates source will yield only 12-14% alcohol. Higher alcohol content is obtained by distilling the fermented material to concentrate the alcohol.

Production of vinegar: Wine and beer provide the initial material for making vinegar. A gram –ve rod shaped organism in genus Acetobacter carries out oxidation of ethanol. C2H5OH + O2 CH3COOH + H2O. When Acetobacter oxidizes the ethanol, present in the beer or wine, the result will be vinegar. The various types of vinegar are produced by different starting materials, thus the use of apple wine yields cider vinegar, grape wine produces wine vinegar and beer results in malt vinegar. The actual production may utilize a batch method whereby, a barrel is filled with wine or beer before it is inoculated with Acetobacter. A continuous generator consisting of column filled of wood shaving is used. Acetobacter develops on the surface of shavings and liquid is percolated through column and alcohol is converted to acetic acid.

Production of industrial chemicals

Different chemicals can be synthesized by micro chemicals but Industrial chemicals which can be prepared by microorganisms at industrial level are:

• Ethanol
• Acetone
• Butanol
• Lactic acid
• Acetic acid
• Citric acid.

The following sections will provide summary of few such products.

Organic solvents

Ethanol, acetone and butanol are mainly made from petroleum. However, in past they have been prepared commercially through microbiological fermentations. If price of petroleum continue to rise, it is probable that microbial synthesis will again be the major source of these chemicals. Some countries such as Brazil have established huge industries to ferment molasses to ethanol with objective of using ethanol to replace gasoline as fuel. Keep in mind that starch in corn or barley must be broken down enzymatically into sugars before the yeast can be fermented. The industrial alcohol produced by this method is mixed 1:9 with gasoline and sold under the name of gasohole. It seems unlikely that conversion of starch into ethanol for fuel will ever become major industry.

Enzymes

Hundreds of tons of bacterial enzymes are produced annually. Commercially important enzymes include:

• Gluco amylase
• Alpha amylase
• Glucose isomerase
• Protease.

Glucoamylase and alphamaylase are used to hydrolyze starch into glucose. Glucose itself is not terribly sweet but by converting into fructose using enzymes glucose isomerase, soft drink industry obtains sugar that is many times sweeter. The bacterial protease includes enzymes (made from Bacillus Licheniformis) that are able to hydrolyze protein into soluble peptides. Other proteases are used as meat tenderizers to convert those tough steaks into filet mignom. Lysine and methionine are added as supplements to animal foods in animal food industry. Methionine is made synthetically but about 40,000 tons of lysine is produced annually as bacterial products. Glutamic acid, an amino acid, is widely used as flavor enhancer in the form of mono sodium glutamate. About 30,000 tons of this amino acids are produced each year from bacterial degradation of glucose.

Production of pharmaceuticals

Antibiotics are the largest and most important class of pharmaceuticals made by microorganism. Synthesis of antibiotics appears to have no role in growth and reproduction of microorganisms. Such products are therefore called as secondary metabolites. The selection of various nutrients by microbial geneticist as resulted in strains of mould and bacteria that produce hundreds of times more antibiotics than did the original parental strains. The second area in which microorganisms are intimately involved in the synthesis of pharmaceutical products has been termed as bio conversion. Here microorganisms catalyze few steps of synthesis; the remaining process is accomplished chemically. E.g. Conversion of plentiful 6-carbon alcohol sorbitol into sorbose by an organism in genus Gluconobacter. The sorbose is then easily converted chemically into vitamin C. such bioconversion along with number of chemical steps are used to synthesize harmones such as cortisone and prednisone.