Microbes have been employed for product generation, like wine, bread etc, since thousands of years. The use of microbes to obtain a product of economic value constitutes industrial microbiology. Any process mediated by or involving micro-organisms in which a product of economic value is obtained is called fermentation. Microbial biomass production has been developed into an industrial activity to obtain protein rich food.
A. FOOD AND DRINK
- Single Cell Protein
Biomass produced by unicellular and multicellular organisms like bacteria, yeast, filamentous fungi and algae is processed and used as human food or animal feed supplement.
This biomass is called Single Cell Protein (SCP) as it is rich in protein.
The micro-organisms used for SCP production must be
i. non pathogenic to plants, animals and man
ii. of good nutritional value
iii. easily and cheaply produced
iv. toxin free.
A variety of substrates are used for SCP production. These range from inorganic carbon (CO2), industrial effluents, confectionary effluents, (whey etc.,), cellulosic wastes (like straw etc.) to high cost materials like starch hydrolysate.
Process of SCP Production from any Micro-organism or Substrate would have the Following Basic Steps
- Provision of a carbon source.
- Addition to the carbon source, a sources of nitrogen phosphorous and other nutrients needed to support growth.
- Prevention of contamination.
- Selected M.O. is inoculated in a pure state
- SCP processes are highly aerobic so proper aeration should be there.
- The microbial biomass is recovered from the medium.
- Processing of the biomass for enhancing its usefulness and/or stability.
B. DAIRY PRODUCTS
Milk drawn from a healthy animal contains several hundred to thousand micro-organisms. In dairy industry various fermented milk products are produced by inoculating pasteurized milk with known cultures of micro-organisms referred to as Starter Culture.
Some of the important fermented milk products are butter milk yoghurt butter and various kinds of cheese.
A simple flowsheet for product ion of plain yoghurt is boxed below:
Fig. 53.2. Flow chart for production of set-type plain yoghurt.
Buttermilk is obtained from pasteurized skim milk cultured with lactic acid and aroma producing organisms. Streptococcus lactis may be used as starter culture.
The term buttermilk is also used for a phospholipid rich fluid fraction obtained as a by-product doing the churning of cream in butter manufacture. However, cultured buttermilk is a viscous, cultured, fluid milk containing a characteristic pleasing aroma and flavor.
C. BAKING AND BREWING
In baking process of food let us take the example of bread making. Micro-organisms are useful in two chief ways in bread making:
a. They may produce gas to leaven or raise the dough giving the bread or any food the desired loose, porous texture.
b. They may produce desirable flavoring substances.
Dough is usually leavened by bread yeasts which ferment the sugars in the yet dough and produce mainly CO2 and alcohol. It can be done by addition-of ammonium bicarbonate. Alcohols, acids, esters and aldehydes are the products that may be added to give desirable flavors.
Although the interior of the loaf does not require to reach 100oC during baking yet the heat serves to kill the yeasts, inactivate their enzymes and expands the gas present and set the structure of the loaf. Baking besides producing the appearance of the loaf also contributes desirable flavors.
Beer and alcohol are the principle malt beverages produced and consumed in our country. They are made of malt hops, yeasts, water and malt adjuncts.
Brewing of Beer
The manufacture of beer as an example of the brewing process. The different steps involved are:
(a) Malting. In the preparation of malt, barley grains are soaked or steeped at 10 – 15oC, germinated for 5-7 days.
(b) Mashing. The purpose of mashing process is to make valuable portions of the malt and malt adjuncts soluble as much as possible. The main mash is prepared by mixing the ground malt with water at 38-50 oC. To this are added cooked starchy malt adjuncts in water, after cooking under steam- pressure;
(c) Fermentation. A special beer yeast of the bottom type, a chain of saccharomyces is used for the inoculation of the cooled wort. During fermentation, the yeast converts the sugar in the wort chiefly to alcohol and carbon dioxide.
(d) Aging or Maturing. The young or green beer is stored or lagered in vats at about 0 oC for several weeks to several months, during which period precipitation of proteins, yeast and other undesirable substances takes place and the beer becomes clear and matured.
D. MEDICAL PRODUCTS
A large number of human genes have been encoded and hence pharmaceutically valuable proteins have been cloned and expressed in micro-organisms. Initially E. coli was used as the host for reasons of case in cloning. But yeast is fast becoming the host of choice for production of recombinant proteins.
Several of the recombinant proteins are used for treatment of the diabetes mellitus (insulin protein), dwarfism [(protein-human growth hormone hGH)], etc. Many other useful recombinant proteins are in advanced stages of development.
1. Production of Human Insulin (Humulin)
Human insulin is a dimer comprising one chain of 21 amino acids (A chain) and the other of 30 amino acids (B chain). Both chains A and B are derived from a single polypeptide chain called as preproinsulin, which has the following sequences:
(1) an N’ terminal leader.
(2) the B chain sequence.
(3) the C-chain that links the A and B chains.
(4) Cvterminal A chain.
The preproinsulin folds spontaneously to yield proinsulin and chains A and B becomes linked by two disulphide bridges. This is followed by cleavage of the leader and the C-chain sequences leaving the mature insulin molecule. It is important that the insulin molecule is not glycosylated making its production ill E. Coli feasible.
Flow Sheet of Production of Mature Insulin
Drug designing aims at designing drugs, which selectively and specifically fits into the critical sites of the target molecules, thereby inactivating the latter.
The target molecule may be
(a) a receptor (45% of the cases)
(b) an enzyme (20% of cases)
(c) ion channel (5% of cases)
(d) DNA (2% of cases)
(e) nuclear receptor (2% of cases).
The aim of drug designing is to develop highly efficient drugs, which have little or no side effects.
The three main steps in drug designing are:
(i) detailed knowledge (including the three-dimensional structure) of the critical sites of target molecules.
(ii) designing of drug molecules which will specifically fit into and bind to these critical sites and synthesis of such molecules.
(iii) evaluation of the interaction of the synthesized drugs with the target molecules, and further modifications in the former to make them ‘safe’ for medical use.
Drugs are normally delivered either orally or by injection. They become distributed in the whole body tissues and fluids and only a small portion reaches the diseased tissue/organ. This necessitates a much larger dose of expensive drugs and may often produce several undesirable effects in other organs/tissues.
The oral route of drug administration is much more desirable than that by injection. But this route is unsuitable for the new class of protein/peptide drugs due to poor uptake. This is because of proteolytic degradation in the gastro- intestinal tracts and poor permeability of the intestinal mucosa to these high molecular weight therapeutic agents.
Some of the approaches developed for a more efficient and targetted delivery of drugs are other routes for example nasal, buceal, rectal routes; drugs can be encapsulated in liposomes: polymers used as drug delivery systems.
Antibiotics are the metabolites having preferential antimicrobial activity. Therefore they are widely used for curing of human ailments caused by micro-organisms.
The antibiotic penicillin was discovered by Fleming in 1929 but its commercial production could commence only during early 1940s. Antibiotic compounds are used either in their natural form or as semisynthetic derivatives; the latter are usually produced by isolating the antibiotic nucleus and subjecting it to chemical modification.
Steps in the Production of Antibiotics:
- Inoculum. A high yielding strain is a prerequisite for antibiotic production. Constant strain improvement is an integral part of production. The improved strains are kept in long term storage.
- Fermenter. Antibiotics are generally produced in stainless steel fermenters used in batch or fed-batch mode. Agitation is mostly done by impellers. Water cooling is done to maintain the temperature. Sterile air is supplied as per need.
In most cases, it is critical to prevent contamination. The final stage fermenter is preferably used for antibiotic production for the longest possible period.
- Production Media. Antibiotic production employs a variety of media, a different one for each stage of production. Seed stage and production media are used. A typical production media has about 10% (w/v) solids. Generally yields are much higher on complex media. In some cases a suitable precursor is provided.
For example for penicillin-G production, phenylacetic acid is used as precursor.
In contrast the seed stage medium is devised for rapid growth and to prevent antibiotic production.
In production processes, the production fermenter is run in batch mode in which a nutrient is added continuously throughout the fermentation to enhance the duration of antibiotic production. Antifoaming agents are added to prevent the foaming.
- Recovery. At the end of final production stage incubation, the froth contains only a low concentration of the antibiotic.
The initial step in antibiotic recovery is separation of cells