This is a unique introductory textbook that covers all aspects of both chemical and bioprocess engineering and provides a thorough grounding in the fundamentals so that the background may be used in future work. The biological background provided enables students to comprehend the major problems in biochemical engineering and formulate effective solutions.
Author : James E. Process Biotechnology, fundamentals of microbiology, immobilization, enzymes, bioreactor sterilization, fermentation technology, aeration and agitation in bioprocess, separation process in product recovery, important topics of scale-up of operation, bioreactor instrumentation and control, principles of effluent treatment and bioprocess engineering and medical applications are covered.
This book will be ready reference to postgraduate students and also useful to practicing process engineers working in the biotechnology based industries. Salient Features Important aspects of Upstream and Downstream process of biotechnology have been covered with suitable illustrations Efforts are made to emphasis on application of basic biological principles to bioprocess engineering Various figures are provided at appropriate places along with photographs to aid students for comprehensive understanding of the subject Review questions have been added at the end of each chapter.
Beginning with a historical review and essential concepts of biochemical engineering in part I, the next three parts are devoted to a comprehensive discussion of various topics in the areas of life sciences, kinetics of biological reactions and engineering principles.
Having described the different building blocks of life, microbes, metabolism and bioenergetics, the book proceeds to explain enzymatic kinetics and kinetics of cell growth and product formation. The shorthand form of the Haworth projection eliminates the Hs and indicates OHs by dashes. Five- and six- membered cyclic sugars are called furanose and pyranose, respectively.
Industrial Applications of Enzymes 73 Figure 4. However, despite the inaccuracy of the Haworth formulas, they are used more frequently than the chair conformation, because they are easier to draw and interpret.
Fructose is a keto sugar and is found in fruits and honey. Fructose sweeter than other natural sugar. If we take the relative sweetness of cane sugar as one, glucose is measured to be 0.
Figure 4. Maltose and cellobiose are repeating units of polymeric starch and cellulose, respectively. Disaccharides may hydrolyze to form two monosaccharide molecules. For this reason sucrose is termed a nonreducing sugar. Sucrose is the only nonreducing sugar among the four disaccharides. Lactose, sugar present in milk, is a dimer of fi-D-galactose bonded 1' - 4' with D-glucose. The aldehyde group of the left ring of lactose is used for linkage.
However, the right ring of the lactose can be opened to react because its aldehyde group is not used for linkage. As a result, lactose is a reducing sugar. Further hydrolysis of maltose yields two molecules of glucose. Cellobiose, a stereoisomer of maltose, is obtained by the partial hydrolysis of cellulose.
Maltose and cellobiose are both reducing sugars, since the right rings may open to react, as reducing agents. One of the most important polysaccharides is starch, which is produced by plants for food storage. Animals produce a related material called glycogen. Starch comprises a large percentage of cereals, potatoes, corn, and rice. Complete hydrolysis of starch yields glucose, but partial hydrolysis gives maltose as well.
This shows that starch is a polymer of glucose units, joined by a-glycosidic linkage. Starch can be separated into two mam fractions by treatment with hot water. The glucosyl residues glucose minus water of amylose are linked by a 1' - 4' glycosidic bonds in a single chain that contains up to 4, glucose units Figure 4. The long linear molecule of amylose exists as a helix that contains six glucosyl residues per turn. Amylopectin is a highly branched amylose. Various length of the linear chains, a 1' - 4' glucans containing 20 to 25 residues, are linked to a core chain by a 1' - 6' glycosidic bonds Figure 4.
Amylose and amylopectin are degraded by a- and f3-amylase, which are found in the pancreatic juice and saliva of animals, a-amylase is an endoglycosidase which attacks the amylose and amylopectin randomly along the a 1' - 4' bonds. Neither enzyme can hydrolyze the a 1' - 6' branch points, which can be degraded by other enzymes, called debranching enzymes. Enzymatic hydrolysis of starch by sequential treatment with a-amylase and glucoamylase will produce glucose as the mam final product.
They are used in infant food because they are easier to digest than starches. Dextrins are sticky when wet and are used as mucilage on postage stamps and envelopes. Cellulose is the most abundant organic compound of natural origin on the face of the earth. Complete hydrolysis of cellulose gives glucose. The cellulose molecule is comprised of long chains of cellobiose molecules joined together by fi-I,4-glucosidic bonds as shown in Figure 4.
The molecular weight of cellulose ranges from , to , 1, to 3, glucose units. The digestive systems of man and most other animals except ruminants do not contain the necessary enzymes cellulase for hydrolyzmg p-glucosidic linkages.
However, cellulases are found in ruminants, various insects, fungi, algae, and bacteria. High-fructose corn syrup HFCS is approximately twice as sweet as sucrose. It is used in soft drinks, canned fruits, lactic acid beverages, juice, bread, ice cream, frozen candies, and so on. HFCS can be obtained from a variety of cereals and vegetables, such as corn, wheat, rice, potatoes, and cassava.
Corn is the most important source of HFCS because of low costs and excellent utilities of its by-products, corn meal, oil, gluten, germ, and fiber. The steeping lasts about 40 hours. The sulfur dioxide inhibits fermentation and helps softening of the kernel.
The steeped corn kernels are torn apart in a degerminating mill to free the germ containing corn oil and to loosen the hull. The germ is separated in a continuous liquid cyclone, washed, and dried for oil recovery. Starch and hull are ground and screened to eliminate the hull.
The resulting mill starch contains 5 to 8 percent protein which is separated in a centrifuge. The separated-out starch is further purified in a hydroclone to reduce the protein content to a minimum level of 0. Industrial Applications of Enzymes 77 fi!. The syrup produced has D. The enzyme used for this step, a-amylase, is thermostable and splits the starch at the interior of the molecule Joglekar et al. After liquefaction, the syrup is further hydrolyzed to glucose by the action of fungal glucoamylase, which acts on starch by splitting glucose units from the nonreducing end.
After saccharification, the liquor 95 percent free glucose is filtered, and passed throug. It is then concentrated in an evaporator to 60 percent solids. The glucose syrup obtained is isomerized to fructose by passing through an immobilized isomerase colum. The glucose isomerase is immobilized by an inert carrier, such as glass beads or DEAE- cellulose.
A typical residence time is 30 minutes. The isomerization reaction is reversible with an equilibrium constant of about 1. Therefore, the expected final concentration of fructose will be less than half of the inlet glucose concentration. The finished product leaving the reactor contains 42 percent fructose, 50 percent glucose, and other saccharides.
After isomerization, the syrup is purified by passing through a filter and ion-exchanger and is concentrated in an evaporator. Cellulose is a renewable resource that is inexpensive, widely available and present in ample quantities. Large amounts of waste cellulose products are generated by commercial and agricultural processes. In addition, municipal facilities must treat or dispose of tremendous quantities of cellulosic solid waste.
Cellulose provides strength and flexibility, while lignin supports and protects the cellulose from biological and chemical attack. Hemicellulose bonds lignin to cellulose. Native cellulose is basically composed of microfibrils, which are bundles of lamellae containing an indefinite number of fibrillar units. Their schematic representation is shown in Figure 4.
Cellulose molecules, hydrophilic linear polymers, are linked together to form elenzentary fibrils or photofibrils , about 40A wide, 30A thick, and A long. The linear polymers in an elementary fibril are oriented in a parallel alignment and are bounded by hydrogen bonds to form a crystalline region, which is surrounded by a disordered layer of cellulose molecules, an amorphous region or paracrystalline region Ranby, Microfibrils in cell wall components are again surrounded by hemicelluose layer and lignin.
Lignin is a complex aromatic biopolymer of high molecular weight and is formed by the polymerization of oxidatively formed radicals of p-hydroxycinnamyl alcohols Hira et aI, It should be noted that the term lignin cannot be regarded as one individually defined compound, but rather, as a collective term for a whole series of similar, large polymeric molecules which are closely related structurally to one another.
The complexity of the chemical structure of lignin makes it very difficult to utilize except as a fuel. Since isolated lignin is a by-product of the pulp industry, its economical utilization has been actively sought. Because of its relatively high calorific value 12, BTU lib , lnost of waste lignin is being used as fuel in the chemical recovery processes of the pulp plants.
Only a small part of lignin is utilized in adhesives, structural polymers, coating, dispersants, soil conditioner, pesticide carrier, and so on. Several processes for the conversion of polymeric lignin to simple chemical feedstock have been developed. However, y vanillin, dimethyl sulfide, and methyl mercaptan are produced in commercially significant quantities Drew et al. Hemicellulose or polyose is primarily composed of xylan, a branched polymer composed of five-carbon sugar, xylose.
Typical polymerization degree of hemicellulose is 50 - , which is shorter than the cellulose molecules. These obstacles necessitate a costly pretreatment step in which elementary cellulosic fibrils are exposed and separated. Many pretreatments have been employed to enhance the degradation of lignocellulosic materials to glucose.
The treatments fall into two general areas Ryu and Lee, : 1. Ball milling is the most commonly used pretreatment. It reduces crystallmity and particle sizes, while it increases surface area, bulk density, and the water soluble fraction. The major drawbacks of the milling are cost and the fact that noncellulosic substances are not removed.
Common chemical pretreatments of alkali and acid contacting improve hydrolysis by breaking down the lignin, hemicellulose, and cellulose. However, chemical hydrolysis is not specific and a variety of products are formed. A balance must be met between the enhanced hydrolysis and production.
Deligmfication treatment, such as Kraft and sulfite pulping used in the pulp-and-paper industry, is too expensive to be considered as an economical pretreatment.
The rate and extent of enzymatic hydrolysis was found to be increased significantly by combining the pretreatment and reaction steps into one process Kelsey and Shafizadeh, ; Ryu and Lee, ; Deeble and Lee, ; Jones and Lee, The separate processes can be combined by using an attrition bioreactor, which is a stirred reactor with stainless-steel balls Ryu and Lee, ; Deeble and Lee, ; Jones and Lee, By using this reactor, the amount of time required for the hydrolysis of newsprint or sawdust can be reduced to hours as compared to days which are necessary in a regular stirred reactor.
Enhanced conversion of cellulose in the attrition bioreactor is due to a combination of fact ors, including a reduction in crystallmity, an increase in pore volume and surface area, and an increase in the accessibility of glucosidic bond sites to the cellulase complex.
It was also found that enzyme deactivation in the attrition bioreactor is not significant, since interfacial forces, not shear forces, cause the most deactivation.
Elimination of the air- liquid interface by covering the reactor substantially increased the enzyme stability. Industrial Applications of Enzymes 81 4.
They are Trichoderma T reesei, T. Bacterial species such as Cellulomonas along with Clostridium thermocellum can also produce cellulases Marsden and Gray, The cellulase enzymes produced by submerged fermentation of the cellulolytic microfungus Trichoderma are usually classified into three general categories: endo-fj,I,4 glucanases endoglucanases , cellobiohydrolases, and ,4 glucosidases cellobiase.
Typical proportions of the endoglucanases and cellobiohydrolases in the extracellular protein from Trichoderma reesei grown in cellulose are 15 percent to 20 percent and 35 percent to 85 percent, respectively. The cellobiase makes up less than 1 percent of the protein Marsden and Gray, The endoglucanases hydrolyze cellulose molecules randomly along the molecule and are more effective in combination with cellobiohydrolases.
Cellobiohydrolases cleave cellobiose and glucose from the nonreducmg end of the cellulose molecule. Endoglucanases and cellobiohydrolases must be absorbed by the cellulose before a reaction can occur, producing soluble sugars and oligomers. Various enzymes have been reported to be susceptible to deactivation upon shearing due possibly to the disturbance of their tertiary structure.
Several investigators have studied the interfacial deactivation of T. The addition of a surfactarlt has been found to substantially reduce enzyme deactivation.
The surfactant impedes the migration of enzyme to the air-liquid interface. Consequently, less enzyme reaches the interface, where it will deactivate by unfolding when subjected to surface tension forces. The cellulase deactivation due to this interfacial effect combined with the shear effect was found to be far more severe and extensive than that due to the shear effect alone Kirn et aI.
The basic assumptions for the derivation of models are summarized in Table 4. Cellulose materials are composed of a highly ordered crystalline phase and a permeable amorphous phase. Some considered this multiplicity of cellulose structure and others ignored it and assumed that cellulose is a homogeneous material. Concerning the enzyme acted on the substrate, some researchers considered all three components of the cellulase enzyme system endoglucanases, cellobiohydrolases, and cellobiase.
Since the kinetic behavior of the three enzyme system are different and not fully understood, simplified models were also suggested by assuming the cellulase system can be represented quantitatively by a single enzyme.
To illustrate the procedure for the development of kinetic models of the cellulose hydrolysis, let's examine the model proposed by Ryu et al. A kinetic model for the enzymatic hydrolysis of cellulose "vas derived based on the following assumptions: 1. The cellulosic material So is composed of amorphous matter Sal crystalline matter SCI and nonhydrolyzable merts Sx' and their rates of enzymatic degradation are different.
The products glucose and cellobiose in11ibit the cellulase enzyme competitively. The reaction scheme based on the preceding assumption can be written as follows: E At low enzyme concentration KeC E « 1 , Eq. This is known as pseudo-steady-state assumption. The change of the intermediate concentrations are: 4. NaOH 3. Rochelle salts sodium potassium tartrate 5. Dissolve the Titrate 3 mL sample with phenolphthalein with 0.
It should take mL of 0. Dilute the standard glucose solution to make 0. Use these known gilicose solutions as samples for step 3 and 4. Prepare a calibration curve which shows the absorbance versus glucose concentration. Dilute a sample so that the expected concentration is in the range of the calibration curve. Place in boiling water for 5 minutes. Cool to room temperature. Read light absorbance at nm with a water blank. Read the value of glucose concentration corresponding to the absorbance from the calibration curve.
In describing the activity of the cellulase, one IV is equivalent to the strength to release 1JLmoies of glucose per minute, because the moleclliar weight of the substrate, cellulose polymer, is not well defined. Frequently we use filter paper as a substrate for the measurement of cellulase activity because it is well defined and yields reproducible results. The experimental procedure to measure the FI-'U of cellulase Mandels et al. Whatman No. DNS reagent Assay Procedures: 1. Dissolve 0.
You are going to measure the enzyme activity of this solution. Coil the filter paper strip and put it in a small test tube. Add 0. Stop the reaction by immersing the test tube into an ice bath. Take 0. If the sample amount is 0. Add 3 mL of DNS reagent to stop the reaction. Cool to room temperature and read light absorbance at nm using water asa blank. Read the glucose concentration corresponding with the absorbance from the calibration curve.
Louis, MO 3. Pour mL O. Start the hydrolysis reaction by adding 6 g of cellulose into the vessel. Take 3 mL sample once every hour and continue the experiment several hours. DetermiIte the total reducing sugar content in the sample by using the DNS method and prepare a curve to show the change of the reducing sugar concentration with time. Industrial Applications of Enzymes 89 4.
The substrate is pure cellulose, which is assumed to be a material with a uniform quality. The products glucose and cellobiose inhibit the cellulase enzyme competitively. The cellulosic material So is composed of amorphous Sa' crystalline Sc' and nonhydrolyzable inert part Sx' and their rates of enzymatic degradation are different.
The cellulose is first hydrolyzed at its surface to cellobiose by the synergistic action of enzymes, endoglucanases and cellobiohydrolases, which are denoted as E Cheng, Y. Deeble, M. Drew, S. Kadam, S. Shoemaker, W. Glasser, and P. Sere 74, Fan, L. Fengel, D. Polymer Sci. Part C 36 Hira, A. Barnett, C. Shieh, and J. Montecalvo, Jr. Sere 74, : Howell, J. Huang, A. Joglekar, R. Clerman, R. Ouellette, and P. Cheremisinoff, Biotechnology in Industry, pp.
Industrial Applications of Enzymes 91 Jones, E. Kelsey, R. Kirn, M. Lee, D. Ryu, and E. Mandels, M. Andreotti, and C. Roche, "Measurement of Saccharifying Cellulase,"Biotechnol. Marsden, W. Miller, G. Okazaki, M. Peitersen, N. Ranby, B. Sere 95 : Reese, E. Ryu, D. Lee, T. Tassman, and C.
Ryu, S. It covers only what is necessary for understanding the terminologies and procedures introduced in this book. Today, the use of microorganisms is even more widespread than before. They are not only used for the traditional microbial processes but also for new processes such as the production of pharmaceuticals, industrial chemicals, enzymes, agricultural chemicals, waste water treatments, mineral leaching, and recombinant DNA technologies.
The protists refer relatively simple biological organisms compared to plants and animals and include algae, protozoa, fungi, and bacteria. The development of the electro microscope allowed the scientists to recognize that unit structure of all living organisms are divided into two category, prokaryotes and eukaryotes. The prokaryotic cell is the unit of structure in two microbial'groups: bacteria and blue-green algae. The prokaryotic cell is small and simple, as shown in Figure 5.
The cell has only two structurally distinguishable internal regions: cytoplasm and nuclear region or nucleoplasm. The cytoplasm has grainy dark spots as a result of its 1 It is recommended that readers obtain any college-level textbooks in biology and micro- biology for further reading and reference as the need occurs. Cell Cultivations 93 content of ribosomes, which are composed of protein and ribonucleic acid RNA.
The ribosome is the site of important biochemical reactions for protein synthesis. The nuclear region is of irregular shape, sharply segregated even though it is not bounded by membrane. The nuclear region contains deoxyribonucleic acid DNA , which contains genetic information that determines the production of proteins and other cellular substances and structures.
Table 5. The prokaryotic cell is surrounded with a cell wall and a cell membrane. The cell wall, considerably thicker than the cell membrane, protects the cell from external influences. The cell membrane or cytoplasmic membrane is a selective barrier between the interior of the cell and the external environment.
The largest molecules known to cross this membrane are DNA fragments and low-molecular-weight proteins. The cell membrane can be folded and extended into the cytoplasm or internal membranes.
The cell membrane serves as the surface onto which other cell substances attach and upon which many important cell functions take place. The more complex eukaryotic cell is the unit structure in plants, animals, protozoa, fungi, and algae.
The eukaryotic cell has internal unit membrane systems that segregate many of the functional components of the cell, as shown in Figure 5. They are 1, to 10, times larger and more complex than prokaryotic cells. The nucleus is surrounded by a double membrane with pores 40 to 70 mJ.! The nucleus controls hereditary properties and all vital activities of the cell.
The chromosomes are long and threadlike bodies and are found in the nuclei of cells, which contain the genes arranged in linear sequence in nucleoproteins proteins plus nucleic acid. The cytoplasm contains large numbers of granules called ribosome, which are involved in continuous reactions to synthesize cell materials. The ribosome is especially concentrated along the rough surface of the endoplasmic reticulum, an irregular network of interconnected membrane-delimited channels.
The mitochondria contain the electron transport enzymes that utilize oxygen in the process of energy generation. Vacuole and lysosome are organelles that serve to isolate various chemical reactions in a cell. Microbial Nomenclature: Microbiologists use the binomial system, in which each organism has two names, for example, Bacillus subtilis. Proper names of organisms are always italicized.
The first word is the name of the genus plural, genera and is capitalized. The genus name is a Latin or Greek word. Salmon, Latinized Saccharomyces: sugar fungus The second word in the name of a microorganism is the species name and is not capitalized. There may be several species with the same genus name, for example, Bacillus subtilis, B. Note that when the same genus name is repeated several times, it is abbreviated For industrial applications of microorganisms, bacteria and fungi are especially important.
Therefore, they are discussed in more detail in the following sections. There are about 1, known species occurring in practically all natural environments. The typical diameter of the cell ranges from 0. The lengths of bacterial cells vary greatly. Bacteria occur in a variety of shapes such as: cocci: spherical or ovoid bacilli: cylindrical or rod shaped spirilla: helically coiled Growth Pattern: Bacteria reproduce predominantly by a process known as binary fission as illustrated in Figure 5.
This process involves several steps: cell elongation, invagination of the cell wall, distribution of nuclear material, formation of the transverse cell wall, distribution of cellular material into two cells, and separation into two new cells.
This is an asexual reproductive process. Nutritional Requirements: It is important to be able to cultivate bacteria under laboratory conditions to study their characteristics. To be able to do this, one must know what food material and physical conditions are required.
Bacterial cells that are actively growing are about 90 percent water. The elemental composition of bacteria is listed in Table 5. The nutritional medium to cultivate bacteria should contain those basic con1ponents listed. Sources of energy a. Sources of carbon a. Sources of nitrogen: atmospheric nitrogen, inorganic nitrogen compounds, or other derived nitrogen. Sources of sulfur and phosphorus: elementary sulfur, inorganic sulfur, or organic sulfur. Sources of metallic elements: sodium, potassium, calcium, magnesium, manganese, iron, zinc, copper, and cobalt.
Sources of vitamins. Physical Conditions: After determining the proper nutrients for the cultivation of bacteria, it is necessary to determine the physical environment in which the organisms will grow best. Three major physical factors to be taken into consideration are temperature, the gaseous environment, and pH.
Since microbial activity and growth are manifestations of enzymatic action, and since the rates of enzyme reactions increase 2 Troph is derived from the Greek word trophe which means nourishing. Cell Cultivations 97 with increasing temperatures, the rate of microbial growth is temperature dependent. Depending on the temperature range over which they grow, bacteria are called psychrophiles, 3 mesophiles, or thermophiles. The temperature ranges in which each group are capable of growth and the optimum temperatures are summarized in Table 5.
The principal gases in the cultivation of bacteria are oxygen and carbon dioxide. There are four types of bacteria, according to their response to oxygen: Table 5. Aerobic bacteria grow in the presence of free oxygen. Anaerobic bacteria grow in the absence of free oxygen. Facultatively anaerobic bacteria grow in either the absence or the presence of free oxygen. Microaerophilic bacteria grow in the presence of minute quantities of free oxygen.
For most bacteria the optimum pH for growth lies between 6. Although a few bacteria can grow at the extremes of the pH range, for most species the minimum and maximum limits fall somewhere between pH 4 and pH9. Spore Formation: Some bacteria form spores when growth ceases due to starvation or other causes. Spores are more resistant than normal cells to heat, drying, radiation, and chemicals. Spores can remain alive for many years; however, they can convert back to normal cells at proper conditions.
Spore-forming bacteria are found most commonly in the soil. Gram Reaction: Gram staining is one of the most widely llsed differential staining technique that separates bacteria into two groups: gram-positive and gram-negative. Cover bacterial smear on a slide with crystal violet and let stand for 20 seconds and wash off the stain. All cells stain violet. Cover the smear with Gram's iodine solution and let stand for 1 minute. Crystal violet will form a complex with iodine within cells.
All cells will remain violet. Flood the smear with 95 percent ethyl alcohol for 10 to 20 seconds and rinse the slide with water. Gram-positive cells will remain violet, but gram-negative cells will be colorless. Cover the smear with safranin, a red counterstain, for 20 seconds, wash for a few seconds, and dry. Gram-positive cells will remain violet, but gram-negative cells will become red. There are characteristic differences between most gram-positive and gram-negative bacteria, which can be summarized in Table 5.
Among them, yeasts and molds are industrially important. Yeasts: Yeasts are widely distributed in nature. They are found in fruits, grains and other food containing sugar. They are also in the soil, in the air, on the skin and in the intestines of animals.
Since yeasts do not have chlorophyll, they depend on higher plants and animals for their energy. Their size is 1 to 5 J. The cell wall is quite thin in young cells but thickens with age. Cell Cultivations 99 The most common growth pattern for yeasts is budding, which is an asexual process as illustrated in Figure 5.
A small bud or daughter cell is formed on the surface of a mature cell. The bud grows and is filled with nuclear and cytoplasmic material from the parent cell. When the bud is as large as the parent, nuclear apparatus in both cells is reoriented and the cells are separated. The daughter cell may cling to the parent cell, often even after the cells are divided. The most important yeasts are strains of Saccharol'rLyces cerevisiae, which are used in the manufacture of wine and beer and in the leavening of bread.
Molds: Molds are filamentous fungi Figure 5. A single reproductive cell or spore conidia is germinated to form a long thread, hyphae, which branches repeatedly as it elongates to form a vegetative structure called a mycelium. This consists of a multinucleate mass of cytoplasm within a rigid, much-branched system of tubes.
Since a mycelium is capable of growing indefinitely, it can attain macroscopic dimensions. The most important classes of molds industrially are Aspergillus and Penicillium.
Molds are used in the production of antibiotics, industrial chemicals, enzymes, and food additives. A mixed culture is one that contains more than one kind of microorganism. The necessary steps for cultivating microorganisms are: 1. Preparing a culture medium in which a microorganism cah grow best. Sterilizing in order to eliminate all living organisms in the vessel. Inoculating the microorganism in the prepared medium.
To cultivate microorganisms, culture medium has to be prepared in one of the commonly employed culture vessels: a test tube, a flask, a Petri dish, or a fermenter. There are two main types of culture media: natural or empirical, or complex and synthetic or chemically defined media. They vary widely in form and composition, depending on the species of organism to be cultivated and the purpose of the cultivation.
Natural media are those used on the basis of experience and not on the basis of exact knowledge of their composition and action.
Natural or complex media usually contain peptones, beef extract, or yeast extract. When a solid medium is desired, a solidifying agent such as gelatin or agar may be incorporated into the medium. Examples of a relatively simple liquid and a solid medium that support the growth of many common heterotrophs are nutrient broth and nutrient agar.
Typical growth medium for yeasts is listed in Table 5. They are often required for research purposes. These media have the added advantage that they can be produced with a constant composition year after year. Sterilization: After a suitable culture medium is selected for the cultivation of a specific microorganism, it is poured into a culture vessel.
If you use test tubes or flasks as your culture vessel, the ends of test tubes or flasks should be covered with a suitable closure to allow for the exchange of gases with the atmosphere, yet to keep foreign organisms out of the media. Various types of closures are used in the modern laboratory including cotton plugs, plastic foam, screw caps, metal caps, and aluminum foil. The medium is then sterilized to eliminate all living organisms in the vessel",-The most common method of sterilization is by moist heat steam under pressure in an autoclave.
The time of sterilization depends on the nature of the material, the type of container, and the volume. Inoculation: Inoculation is the seeding of a culture vessel with the microbial material inoculum. The inoculum is introduced with a metal wire or loop which is rapidly sterilized just before its use by heating it in a flame. Transfers of liquid culture are often made by using a sterilized pipette.
TIle inoculation is usually done in a laminar flow hood to minimize the risk of contamination. Koleksiku Bantuan Penelusuran Buku Lanjutan. Dapatkan buku cetak. Belanja Buku di Google Play Jelajahi eBookstore terbesar di dunia dan baca lewat web, tablet, ponsel, atau ereader mulai hari ini. Buka Google Play Sekarang ». Biochemical Engineering Fundamentals. Ollis , David F.. The biological background provided enables students to comprehend the major problems in biochemical engineering and formulate effective solutions.
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