The data obtained from the pour plate should reveal information such as the source of microorganisms, potential shelf life, or possible public health hazards of the product. With the present aerobic plate sys- tem, the source of microorganisms generally is not determined Blanken- agel In most foods, microbial growth causes undesirable changes. Hence, the plate count might be used as an indicator of potential shelf life or of incipient spoilage.
No relationship was found to exist between the bacte- rial count and potential shelf life of iced shrimp Cobb et al. The usual plate count system does not differentiate types of organisms that cause spoilage. Some people believe that a high micro- bial count indicates improper handling with possible pathogens being present.
Quite often the reverse is true, and low-count products contain potential pathogens. Microbial toxins can be present after the bacteria are destroyed by processing. Undesirable Characteristics.
There are many facets of the pour plate system that are undesirable. Of most concern are time, expense, technical re- quirements, information obtained, and accuracy. The prepared plates must be incubated so that the organisms can produce a visible colony prior to counting. This incubation period may range from two to ten days. For highly perishable products, or for deter- mining production or processing conditions, it is desirable to obtain the results as soon as possible.
If a ten-day incubation period is needed, the potential shelf. Since the pour plate system is so common in the United States, we might not realize that it is rather expensive compared to other methods. In some countries, other, less expensive methods are used in preference to the plate count.
The pour plate method seems simple to do, but a trained technician is needed to perform the test. The accuracy of the pour plate depends upon the ability of the technician as well as on assumptions and errors inherent in the technique. The same assumptions and errors in sampling as discussed for the DMC apply equally to the pour plate.
The technical ability and concern of the technician during cleaning of glassware, prep- aration of dilutions and media, sampling, plating, counting, and calculat ing can influence the reported CFU. Two major assumptions of the pour plate system are that 1 microor- ganisms are in suspension as dissociated single-cell units so that each colony on the plate arises from an individual cell; and 2 all cells planted in the medium will multiply and produce a visible colony.
Neither as- sumption is accurate. Quite often bacteria grow in chains or clusters. Mixing, shaking, and other procedures do not always separate these chains or clumps into in dividual cells. Hence, when plated, a colony may arise from not only one, but several bacterial cells.
No one environmental condition will support the growth of all of the types of microbial cells that might be present in a food prod- uct. Hence the bacterial count should be referred to as CFU per gram of food. The main value of a plate count is to be able to compare the results of various samples taken at different times from the different laborato- ries. This is possible only when the results are reproducible. It is impor- tant that standardized procedures be followed so that results can be com- pared.
In this system, the sterile melted and cooled agar is poured in sterile petri plates. After solidification, the plates are preincubated overnight. The incubation dries the surface of the agar so that, when planted, the organisms do not coalesce. Before using, the dried agar surface should be observed for any possible contam- ination.
Aliquots of dilutions are added to the dry surface and uniformly spread over the agar by means of a sterile glass rod, bent into the shape of a hockey stick. Various amounts of aliquots have been suggested. Inas- much as we usually work with dilutions in the order of 10, it is much easier to calculate the results per gram of product if O. For simplification, calibrated loops can be used in place of pipets for preparing dilutions as well as for inoculating the pour plate or the sur- face of the spread plate.
In the plate loop system, a calibrated loop is fitted into the barrel of a repeating syringe. The loopful of sample is flushed onto the agar surface in a petri plate with sterile diluent in the syringe. According to O'Connor , the precision and accuracy of the plate loop system are within acceptable limits. With the drop plate method, 0. Six to eight drops are placed on an agar surface in a petri plate, with no further manual spreading.
After inoculation, the plates are inverted and incubated, and the resultant colonies counted as with the pour plate method. Automated devices for distributing the samples over the agar surface have been described and evaluated Gilchrist et aL ; Gilchrist et aL ; Jarvis, Lach, and Wood ; Kramer, Kendall, and Gilbert ; Tilton and Ryan ; Trotman and Byrne One type of automatic plating system is the spiral plater Fig.
The spiral plater. By varying the amount of inoculum, the equivalent of three dilutions can be plated on one agar surface. After incubation of the inoculated plates, a laser colony counter, developed for the spiral plater, follows the spiral from the outer edge toward the center, counts the colonies, and determines the CFU for the inoculum. Also, the colonies can be counted manually with the use of a spiral grid system. Surface VS. Pour Plates. The desirable aspects listed for the pour plate are equally applicable to the surface plate.
It is well recognized that higher counts are obtained by surface spread plates than by pour plates. The possibility of heat-sensitive organisms being damaged by hot agar during the preparation of pour plates is over- come by using the spread plate technique.
Obligate aerobic organisms will grow faster on the surface than in the depth of agar in pour plates. Surface colonies are always detectable sooner and are much larger and easier to count than are colonies in a pour plate.
The main advantage of surface plates as compared to pour plates is that surface plating can be automated. With automated analyses such as the spiral plate system, both work and materials are saved.
Hence, filtration of the sample may be needed to remove these particles prior to plating. Hoben and Soma- segaran found the drop plate method to be more economical than either the spread or pour plate systems. The undesirable characteristics of the spread plate are similar to those discussed for the pour plate. With the spread plate system, some of the organisms might cling to the glass rod used for spreading.
Treating of the glass rod with silicone helps to overcome the problem. Reportedly, precision with the pour plate is better than with the spread plate.
Dry, Rehydratable Film. As an alternative to the petri plates used in the aerobic plate count systems, plastic films with a dry, rehydratable me- dium coated upon them Petrifilm SM have been developed.
The dry medium contains nutrients, a cold water-soluble gel, and 2,3,5-triphenyl- tetrazolium chloride that is reduced by microbial growth from white to red. The prepared samples or dilutions are added at the rate of 1.
The sample is spread over an area of about 20 cm 2 by applying pressure with a plastic spreader on the overlay film. The liquid in the sample rehydrates the medium, then the gel is allowed to solidify before the prepared films are incubated for bacterial growth. Reportedly, the Petrifilm SM system was a satisfactory alternative to the aerobic plate count for poultry Bailey and Cox , pasteurized fluid milk Senyk et aL , and ground beef Smith, Fox, and Busta The basic idea of the roll tube is the same as for the pour plate method, except that screw-capped test tubes or bottles are used in place of petri plates.
Test tubes are sterilized with 2 to 4 ml of plate count agar with 2 percent agar. When the melted agar is cooled to 42 to 45C, 0. The roll tubes are incubated upside down so that any water that con- denses collects below the inoculated agar and does not smear the colo- nies. After incubation, the colonies that develop are counted with the aid of a low-power magnifier.
Multiplying the colony count by the dilution factor yields the number of organisms per gram of food. Although the basic idea of the roll tube is similar to the plate count, there are obvious differences. Since test tubes are used rather than petri plates, the cost of the procedure may be lower or higher, depending upon the relative cost of these items.
Less plate count agar is used in the roll tube method. This method involves the spreading of a sample over an agar slant with a calibrated loop. Test tubes can be used, but the oval tube gives a larger surface for the growth of colonies. Colonies may be counted or compari- sons can be made as to the extent of growth that occurs so that high- and low-count products can be distinguished. The Burri slant method is a simple test for the evaluation of plant sanitation.
Since Frost introduced the little plate system in , many modifications to the system have been proposed. The origi- nal procedure was to mix 0. After incubation for 3 to 8 hr in a moist chamber, the slides were air-dried, flame-fixed, and stained for counting. The colonies were observed and counted with a microscope. Modifications have been suggested in the procedure, such as the types of slide used, the method of inoculation and incubation, as well as type of stains.
A similar procedure was described by Postgate to distin- guish viable cells from dead cells, since to observe colonies on the slide, the cells must be viable. This system is a more rapid method than the plate count, since only 3 to 8 hr of incubation are used.
Besides being rapid, an estimate of the viable number of cells is obtained, which is not the case with DMC. The little plate, slide plate, and microplate methods give results comparable those for the plate count. When fluids are filtered through a membrane filter MF , all particles, bacteria, or cells larger than the pores are re- tained on the filter surface. The procedure has been useful for analyzing processed water, various beverages, or air when the microbial count is relatively low.
Such low contamination is difficult to evaluate with the APC. More recently, MF systems have been used to analyze foods with relatively high numbers of bacteria. Prefilters are used to remove food particles that might clog the MF. In some cases, surfactants and enzymes, such as proteases, are used to degrade the food so that it can be filtered Bourgeois et al. The retained microorganisms can be cultured by aseptically transfer- ring the filter onto a nutrient agar or one that is selective, differential, or both.
After incubation for 6 to 8 hr, the microcolonies can be counted with a microscope similarly to that used in the little plate or microplate method.
After incubation for 24 to 48 hr, the colonies can be counted similarly to the APC. The bacterial cells can be stained with 0. After destaining the filter and making it transpar- ent, the dye retained by the cells is determined with a spectrophotometer. Reportedly, this reading is related to the number of cells on the filter. A membrane filter with hydrophobic material in a grid pattern is called a hydrophobic grid membrane filter HGMF.
The grids are com- partments of equal and known size, and the hydrophobic material deters the spreading of colonies. After the organisms are grown on the filter, the number of squares containing colonies is enumerated and converted to a most probable number- The results can be determined manually or with an automated counting system sample analyzer.
In one system, the microorganisms on the filter are subjected to a fluorescent dye, acridine orange, which stains viable cells, and then ob- served with an epifluorescent microscope. The DEFT is a rapid method and is especially useful for samples of food containing high numbers of organisms Pettipher ; Qvist and Jakobsen ; Shaw et al. The method was not suitable for heated samples Hunter and McCorquodale ; Rodrigues and Kroll However, a double staining system using acridine orange and janus green B al- lowed the differentiation of viable and heat-killed cells Rodrigues and Kroll The tube dilution method is essentially the aseptic inoculation of a series of tubes of sterile nutrient broth with a series of dilutions of the food.
After incubating the inoculated tubes, the broth is observed for turbidity, which indicates growth of organisms. If no turbid ity is evident, it is assumed that no microorganisms were present or were able to multiply. With broth that appears turbid due to inoculated food, growth can be detected by streaking on an agar surface and observing growth after a few hours of incubation, or by spreading some turbid broth on a slide and looking for microorganisms with the aid of a micro scope.
If the tube with the dilution showed growth and the tube with had no growth, there were between and 1, organisms in the food. Sometimes this rough estimate is all that is needed. It gives only an estimate of the range of bacteria that are present. By using several tubes at each dilution and recording the positive showing growth tubes and negative no growth tubes, you get a more accurate estimate of the number of organisms present.
In the tube dilution example, if you inoculated 10 tubes with 1 ml of the , dilution, there would be as much total inoculum as in the tube which showed growth. Theoretically, one or more of the 10 tubes with the , dilution also should be turbid. The relationship of positive and negative tubes has been determined mathematically and MPN tables have been derived Tables 2. To use the MPN system, at least three dilutions are needed. Ideally, the least dilute tubes should all be positive and the most dilute tubes of the three dilutions should all be negative.
This is not always the case, so the rule that has been established is to select the highest dilution in which all portions tested are positive no lower dilution giving negative results , and the two succeeding dilutions are then chosen.
The more tubes that are used in each dilution, the more accurate is the estimate, but for rea sons of convenience, threetube or five tube series are adopted. After se lecting the three series of dilutions, consult the appropriate MPN table, obtain a most probable number that satisfies the number of positive tubes, and multiply this by the dilution factor to obtain the MPN per gram of product.
Assumptions and Errors MPN. The assumptions and errors due to sam pIing and diluting apply to the MPN technique. Parnow personal communication. Because dilution to extinction is necessary, good aseptic technique is needed, since any contamination during inoculation of the tubes of broth could result in growth. The MPN is less precise than the agar plating methods Pike et al. Some people become confused when 1 g of sample is added to a tube with 9 ml of broth for the MPN series. They feel that since this is a dilution, somehow it has to be considered when the dilution factor for the MPN is determined.
It does not make any difference if there are 8, 9, 10, or 11 ml of nutrient media per tube. The only consideration is the amount of original sample that is added to the tube 0. Advantages of the MPN.
The MPN is, in some ways, easier or simpler to do than the plate count. Broth can be dispensed into tubes with an auto matic pipetter. Selective or differential media can be used so that certain types of organisms can be determined.
Organisms obtain energy from chemical reac- tions involving either organic or inorganic compounds. This involves an oxidation-reduction reaction; the energy source becomes oxidized, while another compound is reduced. Oxygen mayor may not be involved be- cause oxidation-reduction reactions concern electron transfers. When a compound loses an electron it becomes oxidized, and another com- pound which accepts this electron is reduced. Compounds vary in their oxidation-reduction potential, which is the tendency for a compound to give up electrons.
Since these reactions con- sist of electron transfers, they can be measured electrically with a potenti- ometer and are expressed by the electrical unit, the volt.
The oxidation- reduction potential also is called the redox potential. Besides being determined potentiometrically, the redox potential can be determined with indicators or dyes. Many compounds undergo color changes when oxidized or reduced. If such a compound is added to a substrate containing metabolizing bacteria, electrons may be transferred to the indicator, and its color will be altered.
Since the color change of the indicator depends on the metabolic rate of a microbial culture, the larger the number of cells, the sooner the indicator will show a color change. The reduction time is inversely pro- portional to the number of cells present Fig. Although several oxi- dation-reduction indicators could be used, methylene blue, resazurin, and the tetrazoliums are the ones used most often in food analysis.
The reductase tests usually are called dye reduction tests, apparently because the dye methylene blue is used. However, resazurin and the tetrazoliums are not dyes, but indicators Conn During reduction, methylene blue becomes colorless.
This dye has been used to determine the bacterial quality of milk and dairy products such as ice cream Anderson and Whitehead, Also, it has been suggested as a means to predict the sterility of heated food Hall and to estimate the number of bacteria in ground beef Emswiler et al. Relationship between reduction time and microbial load. The slope of the line depends upon the types of microorgan- isms that are present.
Two color changes occur during the reduction of resazurin. The blue color goes through various shades of purple and mauve to pink. This color change is not due to an electron transfer, but to the loss of a loosely bound oxygen atom. This color change to pink is not reversible by atmo spheric oxygen.
The second color change results in the indicator becom ing colorless and is reversible by atmospheric oxygen. The resazurin test is a simple, relatively rapid, inexpensive system to determine the quality of fresh scallop meat Webb et al. The tetrazolium salt most often used for testing food is 2,3,5-triphen yltetrazolium chloride TTC , since it is less toxic to bacteria than are other tetrazolium salts. The TTC is colorless in the oxidized state but forms intensely colored pink to red pigments formazans when reduced.
This indicator can be used to distinguish bacte rial colonies from food particles in an SPC. The reductase test gener ally gives an estimate of the bacterial contamination in a shorter time than the SPC. The information obtained from reductase tests can, at best, be used to obtain a rough estimate of the number of microorganisms present in or on a food. Not all organisms cause a lowering of the redox potential at the same rate. If a clump or chain of bacteria is plated in agar, a single colony will develop, but the metabolic activity in the reductase test will be the sum of the total number of cells in the clump or chain.
This will result in a more rapid color change in the indicator than the plate count would suggest. For a cell to be counted in the SPC, it must multiply and form a visible colony. Cells may be metabolizing, but not reproducing. These cells could cause a color change in the redox indicator and not be included in the SPC.
Methylene blue and tetrazolium are inhibitory to certain microorgan isms. Sometimes tetrazolium is added after the organisms have grown, such as by flooding an agar surface, due to its potential for inhibiting the cells.
It has been suggested that reducing enzymes naturally present in foods can cause color changes of these indicators. In this case, the reduc tase test would indicate more contamination than is present. Everyone makes organoleptic evaluations of food by sight, smell, taste, or touch. The food industry relies on these organoleptic tests to determine certain quality attributes of foods. This type of analysis is very subjective, and many ar guments can develop between seller and buyer.
Chemical indicators can be used to evaluate the quality of food in a more objective manner. Food is composed of various chemical compounds that are subject to biochem ical changes.
These changes may be desirable or undesirable, depending upon the food, the microorganisms that are present, and the end prod- ucts of the reaction. Decomposition of a food with resulting quality dete- rioration is an undesirable change. The main reactions occurring in foods are catalyzed by enzymes. These enzymes may be tissue enzymes naturally present in the food, they may be produced by microorganisms associated with the food, or they may be added to catalyze a desirable reaction see Chapter 9.
Some chemical reactions, such as oxidation, occur in foods without specific en- zymes to catalyze them. The extent of change occurring in the food may or may not be related to the number of microorganisms present. Criteria for Chemical Indicators. For a chemical to be a useful indicator, it must meet the following criteria: 1 it must be absent or at very low levels in sound food; 2 it should be produced by the predominant spoilage flora and not used as a nutrient; 3 it should not be detected quantita- tively with simple and rapid tests and the tests should never yield false positive results; 4 it should not have a useful function in the food; and 5 it should preferably be able to distinguish poor quality from poor processing operations.
Some potential chemicals for estimating the microbial or other quality of food are listed in Table 2. In general, a group of compounds such as vola tile reducing substances, total volatile acids, or bases gives a better indica- tion of quality than a single indicator such as ammonia, indole, or alco- hol. One problem with many of these indicators is that by the time there is a significant change in the amount that is present, deterioration of the food is very evident. Perhaps incubation of the food for a few hours be- fore analysis could be used to develop the presence of indicators more rapidly.
However, this higher temperature could alter the dominant spoilage flora so that the metabolic products would differ from those expected to develop under normal storage conditions. Microbial growth causes alterations in foods, such as acid content or pH. As the pH is varied, the water-binding capacity of protein changes. This difference can be determined by the extract re- lease volume test. Since basic compounds such as ammonia and amines are formed during deterioration of protein foods, the pH will tend to rise.
If carbo- hydrates are present and fermented, the pH will tend to decline. Shelef and Jay recommended blending 10 g of meat with water and titrat- ing to pH 5. If more than 2. As meat deteriorates, there is an increase in the amount of water retained and a decrease in ERY.
Shelef re- ported the relationship between pH and ERY. Regardless of the micro- bial quality of the meat, the maximum ERV occurred at pH 5. During metabolism, cells form high-energy phosphate bonds stored in ATP. Not only microbial cells, but also other living cells contain ATP. When an animal dies and the muscle glycogen is utilized by anaerobic glycolysis, the amount of ATP decreases.
It has been established that when bacterial cells are killed, the ATP disappears. In starved cells, the ATP falls to low levels before the loss of viability is evident.
Since all microbial cells contain ATP, it should be possible to estimate the number of cells by quantitating the ATP in a system. The method for determining ATP is based on the firefly reaction as shown in Figure 2. A purified extract from the firefly, containing luci- ferin and luciferase, when reacted with ATP in the presence of magne- sium ions, causes a light emission.
Crude extracts from the firefly, when reacted with adenosine diphosphate ADP have caused light emission. When the purified firefly extract is added to bacterial ATP, the light emis- sion can be measured with a photometer. For the assay, it is necessary to eliminate the nonbacterial ATP and then to release the bacterial ATP to react with the luciferin-luciferase system.
Reactions involved in adenosine triphosphate determinations. The ATP system is relatively simple and rapid. The system is report edly reliable and acceptable for food and water analysis J arvis ; Pic ciolo et al. Firefly bioluminescence was reviewed by McElroy and DeLuca When organisms metabo lize compounds, carbon dioxide is produced as a metabolic product and oxygen is consumed. One method for determining CO2 production uses 14Clabeled glucose and measures the reactivity of the released 14C0 2 The detection time of 14C0 2 is proportional to the logarithm of the original inoculum Waters This procedure has been used for determining various bacteria in water and food Hatcher et al.
Headspace gas of bottled fruit juice was analyzed for CO 2 by an infra red system Threlkeld Infrared analysis detected 89 percent of the samples that were positive by conventional methods. Most of the false negative samples lacked the presence of fermentative organisms. The metabolic activity of cells changes the chemical composition of a medium, a process that results in altering the imped ance FirstenbergEden and Zindulis This system has been used to estimate microorganisms in cooked food Rowley et al.
Besides those systems described, other systems have been used by microbiologists to develop rapid methods for microbial detection. A pyrolysisgas chromatography- mass spectrometry experiment was used to analyze Martian soil for or- ganic compounds that would indicate life on Mars Klein ; Sim monds Sanders and Parkes attempted to correlate infrared analysis of swabbings from broiler skin with bacterial numbers.
Gas chromatography or gasliquid chromatography has been used to detect metabolic products of microorganisms which can be used to differ entiate bacterial species or estimate the count or quality Carlsson ; Staruszkiewicz and Bond Limulus amoebocyte lysate forms a gel in the presence of small amounts of endotoxin from Gram-negative bacteria. It is not possible to discuss all of the procedures that might be used to determine microorganisms in foods.
Some other procedures were de- scribed by Bordner , Feldman , Goldschmidt and Fung , , Jarvis , Newsom , and Southern Although agar is the usual solidifying agent in solid media, various substitutes have been suggested Cranston ; Kang et al. Comparison of Methods There are many procedures that can be used to estimate the total microbial population of a food product. The test that is selected depends upon the use of the information that is obtained.
If the results are to be used to satisfy a microbiological standard, then the specified method, usually the standard plate count, must be used. If the results are for inter- nal quality control, some other method that is simpler, faster, or less ex pensive might be used. The laboratory equipment and personnel, both now and in the future, will probably dictate the type of analysis that can be conducted.
The cost of supplies, materials, instru- ments, and labor must be compared with other factors to determine which method or methods give the desired information with ease, sim- plicity, speed, and low cost.
In selecting the test, not only precision but also accuracy must be considered. Precision is an index of the random error in a group of de- terminations and is not related to accuracy.
The term accuracy considers the relationship of the determined value and the actual value. Since there is no way to know the actual or true number of microorganisms in a sample, it is difficult to assess the accuracy of a method. Quite often, the results of a method are compared to those obtained with the APC. The results obtained with the APC may not be accurate, but the method yields acceptable reproducibility or precision.
Rapid tests such as those based on metabolic products and instrumen tation are valuable for control purposes. Time is important in analyzing highly perishable foods. Also, it is desirable to keep the inventory of processed food at a reasonable level. If unacceptable product is shipped from storage, it might need to be recalled. A recall of a product and the bad publicity that often results is not desirable for a processor.
If microbial inhibitors are present in the food, these will be carried over into the growth medium. In these cases, as the sample is diluted, higher counts might be obtained due to dilution of the inhibitors. If a food containing glucose is added to a medium designed to determine lactose fermentation, erroneous results may be obtained due to fermen- tation of the added glucose. In processed foods, there may be cells that are sublethally injured.
These are of special importance when the types of organisms are deter mined with selective media. Comparisons of various methods of estimating microbial counts have been published Greenwood et al.
Perhaps food microbiologists have emphasized the socalled total count too much, since spoilage organisms and potential pathogens are more important in a food than are other types of organisms.
However, at the present time, the total count is usually the first microbial characteristic determined for almost any food. A rapid electrical method to detect microbial growth automatically. The validity of the methylene blue reduction test in the grading of ice cream. Anderson, M. Evaluation of swab and tissue excision methods for recovering microorganisms from washed and sanitized beef carcasses.
Lab Manage. Microbiological methods. Enumeration of coliforms in selected foods. Hydrophobic grid membrane filter method, official first action. Horwitz, ed. Washington, D. Standard Methods for the Examination of Dairy Products. Compendium of Methods for the Microbiological Examination of Foods. Speck, editor. Bailey, C. Evaluation of microbiological test kits for hydrocar bon fuel systems. Evaluation of the petri film SM and VRB dry media culture plates for determining microbial quality of poultry.
Barrow, P. A note on a method to aid sampling populations for characteristics. Biltcliffe, D. An assessment of acceptance sampling plans as applied to foodstuffs. Blankenagel, G. An examination of methods to assess post pasteurization contami nation. Milk Food Teelmol. Bordner, R. Microbiology: Methodology and quality assurance. Water PoUut. Contml Fed. Bourgeois, C. Membrane filtration of milk for counting spores of Clostridium tyrobutyricum. Dairy Sci. Brickey, P. Recommendations for offi cial methods.
Simplified gas chromatographic procedure for identification of bacte rial metabolic products. Cobb, B. Chemical charac teristics, bacterial counts, and potential shelflife of shrimp from various locations on the northwestern Gulf of Mexico. Milk Food Technol. Collins, C. Microbiological Methods.
London: Butterworth and Co. Conn, H. Biological Stains. Baltimore: Williams and Wilkins Co. Cook, D. Recommended modification of dilution proce dure used for bacteriological examination of shellfish.
Cowell, N. Microbiological techniques-Some statistical aspects. Food Agr. Cowlen, M. Soaking of mustard seeds to release microorgan isms in making plate counts. Cranston, P. Alginic acid derivatives as a solidifying agent for microbiological nutrient suspension. Comparison of the stomacher with other systems for breaking clumps and chains in the enumeration of bacteria. Dewhurst, E. The use of a model system to com pare the efficiency of ultrasound and agitation in the recovery of Bacillus subtilis spores from polymer surfaces.
Dickens, J. Evaluation of a mechanical shaker for microbiological rinse sampling of turkey carcasses. Poultry Sci. Dijkman, A. Entrapped air as a cause of erroneous milk cell counts Coulter counter. Milk Dairy]. Dodds, K. Evaluation of the catalase and Limulus amoebocyte lysate tests for rapid determination of the microbial quality of vacuumpacked cooked turkey. Emswiler, B. Dye reduction method for estimating bacterial counts in ground beef. Being a medical students, it is very important for a person to learn about all the microorganisms which play an important is spoiling our food and also, the organisms which are good for our food.
To study this vast subject, you are going to need a book like Food Microbiology which enables you to understand all the basic concepts about the microorganisms who are either trying to spoil or make our food better. To download the free Food Microbiology Pdf from our site, use the link given at the end of this post. This book is written by Martin R. Adams who is known for his various contributions to the field of medical sciences. This books he written is especially for those students who want to become a better learner of the subject.
Such students are unable to find a good book but now the really have. The book talks about all the microorganisms such as Bacteria and Cocci who are responsible for certain actions in our food. To learn more about them, get this book on your laptop or mobile to start studying the subject in a better way. To download the free Food Microbiology pdf, follow the link given below and start studying the subject to score good grades.
Keep visiting our website for more free pdfs and book reviews. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Fuente: Vincenzo Cuteri. Fuente: Bellarmine University. Fuente: Gulfport School District. Fuente: USF Health. Fuente: Universitas Syiah Kuala.
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