FOOD MICROBIOLOGY MCB 408
FOOD MICROBIOLOGYMCB 408Course LecturerDr Adeleke OshoFood MicrobiologyBrief history of Food Microbiology. Flora and sources of microorganisms in food. Methods of detection andenumeration of microorganisms in foods. Intrinsic and extrinsic parameters of food that affects microbial growth andsurvival. Roles of microorganisms in spoilage, food borne diseases and in food products. Food preservation. Qualitycontrol and microbiological standardsFOOD MICROBIOLOGY.
BASIC PROCEDURES.1.2.3.4.No eating or talking in food microbiology LAB.All working benches, floor, and environment must be kept clean.Licking of labels and mouth pipetting should be avoided.Where there is a spillage or contamination material this should be coveredwith suitable materials and discarded appropriately.5. Open wound or cut should be covered appropriately or dressed appropriately.6. At strategic places fire extinguishers should be provided.7. All microbiological procedures should be carried out under laminar airflow.8. At all times LAB coats should be worn.9. Nail vanishes and mouth polishing are not allowed in the LAB.10. Hair, moustache, and beard must be covered.11. When centrifuge are used, they must be allowed to stop on their own andgeneration of aerosols should be avoided.12. After each operation, hand cleaning should be done.EQUIPMENT AND MATERIAL USED.1. INCUBATOR: - can be used for aerobic and anaerobic organism at desiredtemperature regimes.2. DRYING OVEN/HOT AIR OVEN: - can be maintained at a temperaturegreater or equal to 120 C.3. LAMINAR AIR- FLOW/INOCULATION HOOD: - Inoculation hood/laminar airflow must be fitted with UV light. All microbiology processingmust be undertaken in this environment.
4. MICROSCOPE: - an optical instrument used for enlarging images of minuteobjects using light and other radiations.5. WATER: - BATH SHAKER.6. COLONY-COUNTER: - for counting colonies.7.BACTOMETER: - for counting colonies in food it takes precedence over thecolony counter.FAST METHODS OF FOOD MICROBIOLOGY. Use of DNA probes Use of impedance method- - BACTOMETER. Use of kits.Kits are used often to identify the organism causing food spoilage, e.g. RAPIDECCOLI/API system all of which are used for identification of unknown organisms.THE IDENTIFICATION, ROLE AND SIGNIFICANCE OF MICROORGANISMS INFOODS.The main source of food to man are of the plant and animal origin. When one considers the typesof microorganisms associated with plant and animal foods in their natural states, one can predictthe general types of microorganisms to be expected on this particular food at some stages in its lifehistory. Based on previous analyses and result obtained from many different laboratories. It hasbeen shown that, untreated foods may contain varying numbers of bacteria, moulds or yeasts. It istherefore important to know nature and the general types of organism normally present undergiven conditions where foods are grown and handled.BACTERIA: - The following consist of the most important genera of bacteria known to causefood spoilage and food poisoning. However some of these are highly desirable in certain KurthiaStreptomyces.MOLDS: Some of the common genera of molds associated with food are as poriumBotrytisMonilia lium
zopusSporotrichumThamnidiumTrichothecium.YEAST: Some of the most common genera of yeast encountered in foods are as rulopsis RY SOURCES OF MICROORGANISM TO FOODS.The primary sources of microorganisms to food are from;1. SOIL AND WATER:In these environment organisms are generally encountered which are often food-bornebacteria are: Alcaligenes, Bacillus, Citrobacter, Clostridium, Corynebacterium,Enterobacter, Micrococcus, Proteus, Pseudomonas, Serratia and Streptomyces amongothers.For molds, some of the most commonly encountered in soils are Aspergillus, Rhizopus,Penicillium, Trichothecium, Botrytis, Fusarium, and others.In the case of yeast, a large number of yeast genera are found in the soil, but their numberare generally low in water.2. PLANTS AND PLANT PRODUCTS.Bacteria that are often found to be associated with plants and plant products areAcetobacter, Erwinia, Flavobacterium, Kurthia, Lactobacillus, Leuconostoc, Pediococcusand Streptococcus. As for molds, the most important plant-borne genera are those thatcause the spoilage of vegetables and fruits and these include Fusarium, Aspergillus,Botrytis, Alternaria etc. The most commonly encountered genera of yeast in plant productsare the genus Saccharomyces, Rhodotorula and Torulas.3. FOOD UTENSILS.The types of food borne microbes that are found in food utensils depend largely on types offood handled, the care of these utensils, their storage and other factors. For example,utensils used in handling vegetables would be expected to have organisms that areassociated with vegetables. Also utensils which have been cleaned with hot or boilingwater will only as its micro flora those organisms that are able to with –stand the treatment.Utensil stored in open place where dust might collect should be expected to have air-bornebacteria, yeast and molds.4. INTESTINAL TRACT OF MAN AND ANIMALS.Organisms generally found in the intestinal tract of man are Bacteroides, Escherichia,Lactobacillus, Proteus, Salmonella, Shigella, Staphylococcus, and Streptococcus. Othersinclude Clostridium, Nitrobacteria, Enterobacter, and Pseudomonas.These organisms, through fecal dissemination in man found their way directly into soil andwater. From soil they may find their way to food utensils. The most encountered yeast inthis case is the Candida.
5. FOOD HANDLERS.The organisms generally found on the hands and outer garments of food handlers are afunction of the environment and the habit of the food handlers. Aside these, there are somebacteria that are specifically associated with hands Nasal cavities and mouth. These includeMicrococcus and Staphylococcus. The genera Salmonella and Shigella are basically foundin the intestine of man, they may be deposited onto foods and utensils by food handlers. Ifsanitary practices are not followed by each individual.Yeast and Molds may be found on the hand, garment of individual depending upon theimmediate history of individual.6. ANIMAL FEEDS.The types of organisms to be found in animal feed would actually depend on the source ofthe feeds, the treatment given them destroy microorganisms, the container in which theyare stored and the like. Any one of the above mentioned genera of bacteria, yeast, and moldmay be found in animal feeds, of particular importance, Salmonella sp. Which causes foodpoisoning?7. ANIMAL HIDES.Mostly organisms in soils, water, animal feeds, dust and faecal matter are often found onthe hides of animal. From the animal hides, the microbes may find their ways into the air,hands of workers and directly into foods. Some members of the hide flora find their wayinto the lymphatic system of slaughtered animals from which they migrate into the muscletissue of the slaughtered animal.8. AIR AND DUST.Majority of genera of bacteria mentioned above except for some pathogens are found in airand dust. Also, many genera of molds and yeast are found. Bacillus and Micrococcus sppare some of the notable bacteria often found in air and dust because of their ability toendure dryness to varying degrees.FOOD EXAMINATIONMethods for the Microbiological Examination of FoodsThis include the following:Direct ExaminationCultural TechniqueEnumeration methods such as (a) Plate count and (b) Most probale numberAlternative method1. DIRECT EXAMINATIONMicrobial CountThe use of optical microscope to examine microbes in food offer some advantages in ashort while. For example, the observation of endospore of Bacillus species underI.
fluorescence microscope quickly gives an idea of the type of organisms in foods. The drawback here is that, the food debris often interfere with the heat fixing and care must be takento prevent smear being washed off during staining. Also, this method does not distinguishbetween live and dead cells. The Direct Epifluorescent filter technique or DEFT is amicroscopy technique that is used for the enumeration of microorganisms in a range offoods such as raw milk. It uses polycarbonate membrane filter which is stained withacridine orange and counted directly under the epifluorescence microscope. The acridineorange is a metachromatic fluorochrome, fluorescing either green or orange depending onthe nature of the molecules within the cell to which it is bound. When bound to doublestranded DNA it fluoresces green byt when bound to single-stranded RNA it fluorescesorange, as long as there is an adequate concentration of dye to saturate all binding sites.Any of the following methods can be used to count microorganisms in food (a) Directmicroscopic count (b) Standard plate count (c) Most Probable Number (d) Impedancemeasurement using a BACTOMETER (e) Dye reduction: this can be used to assess thekeeping quality or otherwise the level of microbial contamination in a given food productparticularly milk. The dyes normally used include the following: RESAZURIN ormethylene blue.In dye reduction test, properly prepare supernatant of food are added to standardsolution of methylene blue or Resazurin and these are observed for colour reduction for e.g.methylene blue is reduced from blue to white, Resazurin is reduced from slate faint blue topink or white. The number of microorganisms present in a given sample is proportional tothe degree of reduction.NOTE; the following are useful factors that affect microbial count.(1) The sampling method used.(2) The distribution of the microorganisms in the food sample.(3) Nature of the food microflora.(4) Nature of the food material biological component.(5) Nutritional status of the culture media used.(6) Incubation temp and the time used for the test.(7) The pH, H20-activity and redox-potential of the medium.(8) Extrinsic factor; - temperature, water vapour, partial pressure of gases of incubation.(9) The type of diluents used.(10) Hygienic nature of the handler.II.CULTURAL METHODThe art of propagating viable propagules to multiply in liquid or solid media is what thatmakes the cultural method. Agar is a polysaccharide with several remarkable propertieswhich is produced by species of red algae. Although it is a complex and variable material amajor component of agar is agarose which is made of alternating units of 1,4-linked 3,6anhydro-L-galactose (L-galactose) and 1,3-linked D-galactose (or 6-O-methyl-D-galactose)
DIFFERENT TYPES OF CULTURE MEDIAClassification:Bacterial culture media can be classified in at least three ways; Based on consistency,based on nutritional component and based on its functional use.1) Classification based on consistency:Culture media are liquid, semi-solid or solid and biphasic.A) Liquid media: These are available for use in test-tubes, bottles or flasks. Liquidmedia are sometimes referred as “broths” (e.g nutrient broth). In liquid medium, bacteriagrow uniformly producing general turbidity. Certain aerobic bacteria and thosecontaining fimbriae (Vibrio & Bacillus) are known to grow as a thin film called ‘surfacepellicle’ on the surface of undisturbed broth. Bacillus anthracis is known to producestalactite growth on ghee containing broth. Sometimes the initial turbidity may befollowed by clearing due to autolysis, which is seen in penumococci. Long chains ofStreptococci when grown in liquid media tend to entangle and settle to the bottomforming granular deposits. Liquid media tend to be used when a large number ofbacteria have to be grown. These are suitable to grow bacteria when the numbers inthe inoculum is suspected to be low. Inoculating in the liquid medium also helps to diluteany inhibitors of bacterial growth. This is the practical approach in blood cultures.Culturing in liquid medium can be used to obtain viable count (dilution methods).Properties of bacteria are not visible in liquid media and presence of more than one typeof bacteria can not be detected.B) Solid media: Any liquid medium can be rendered solid by the addition of certainsolidifying agents. Agar agar (simply called agar) is the most commonly used solidifyingagent. It is an unbranched polysaccharide obtained from the cell membranes of somespecies of red algae such as the genera Gelidium. Agar is composed of two long-chainpolysaccharides (70% agarose and 30% a garapectin). It melts at 95 oC (sol) andsolidifies at 42oC (gel), doesn’t contribute any nutritive property, it is not hydrolyzed bymost bacteria and is usually free from growth promoting or growth retarding substances.However, it may be a source of calcium & organic ions. Most commonly, it is used atconcentration of 1-3% to make a solid agar medium. New Zealand agar has moregelling capacity than the Japanese agar. Agar is available as fibres (shreds) or asPowders.C) Semi-solid agar:Reducing the amount of agar to 0.2-0.5% renders a medium semi-solid. Such media arefairly soft and are useful in demonstrating bacterial motility and separating motile fromnon-motile strains (U-tube and Cragie’s tube). Certain transport media such as Stuart’sand Amies media are semi-solid in consistency. Hugh & Leifson’s oxidationfermentation test medium as well as mannitol motility medium are also semi-solid.D) Biphasic media:Sometimes, a culture system comprises of both liquid and solid medium in
the same bottle. This is known as biphasic medium (Castaneda system for bloodculture). The inoculum is added to the liquid medium and when subcultures are to bemade, the bottle is simply tilted to allow the liquid to flow over the solid medium. Thisobviates the need for frequent opening of the culture bottle to subculture.Besides agar, egg yolk and serum too can be used to solidify culture media. Whileserum and egg yolk are normally liquid, they can be rendered solid by coagulation usingheat. Serum containing medium such as Loeffler’s serum slope and egg containingmedia such as Lowenstein Jensen medium and Dorset egg medium are solidified aswell as disinfected by a process of inspissation2) Classification based on nutritional component:Media can be classified as simple, complex and synthetic (or defined). While most ofthe nutritional components are constant across various media, some bacteria needextra nutrients. Those bacteria that are able to grow with minimal requirements are saidto non-fastidious and those that require extra nutrients are said to be fastidious. Simplemedia such as peptone water, nutrient agar can support most non-fastidious bacteria.Complex media such as blood agar have ingredients whose exact components aredifficult to estimate. Synthetic or defined media such as Davis & Mingioli medium arespecially prepared media for research purposes where the composition of everycomponent is well knownCOMPLEX MEDIA.Pasteur, Koch, and Tyndall typically prepared media by boiling animal orplant materials to extract nutritive molecules. Today, many modern complex media (such asTryptic Soy Agar) contain extracts of beef (peptone), milk (tryptone), soybean meal (soytone),or yeast. The protein in these extracts are broken down into small peptides and amino acids.Although the specific amount of these molecules is not precisely determined, their wideassortment allows complex media to support a wide range of bacterial types.DEFINED MEDIA.Defined media are formulated from pure substances at predetermined concentrations. Thus,unlike complex media, the exact chemical composition of defined media is known precisely.Because the composition is precisely established, defined media are often used to determine thenutritional requirements of bacterial species.SELECTIVE MEDIA. Complex or defined media may also be classified as selective (orENRICHMENT) media, which support the growth of only certain types of bacteria. Media canbe made selective through the addition of substances that enhance or inhibit the growth ofparticular types of bacteria. Media have been developed that are selective for an astonishingdiversity of bacteria, and we will be using many of these media throughout the semester.DIFFERENTIAL MEDIA.Any of the above types of media might also be formulated as a differential medium. Adifferential medium reveals specific metabolic or metabolic characteristics of bacteria grown onit. Differential media are among the most powerful tools available to a microbiologist, revealinga wide range of information about an organism very quickly. Some media are both selective and
differential. For example, the medium called MacConkey Agar is selective for gram-negativebacteria and will indicate whether bacteria can ferment lactose.3) Classification based on functional use or application:These include basal media, enriched media, selective/enrichment media,indicator/differential media, transport media and holding media.A) Basal media are basically simple media that supports most non-fastidious bacteria.Peptone water, nutrient broth and nutrient agar considered basal medium.B) Enriched media: Addition of extra nutrients in the form of blood, serum, egg yolketc, to basal medium makes them enriched media. Enriched media are used to grownutritionally exacting (fastidious) bacteria. Blood agar, chocolate agar, Loeffler’s serumslope etc are few of the enriched media.C) Selective and enrichment media are designed to inhibit unwanted commensal orcontaminating bacteria and help to recover pathogen from a mixture of bacteria. Whileselective media are agar based, enrichment media are liquid in consistency. Both thesemedia serve the same purpose. Any agar media can be made selective by addition ofcertain inhibitory agents that don’t affect the pathogen. Various approaches to make amedium selective include addition of antibiotics, dyes, chemicals, alteration of pH or acombination of these.D) Enrichment media are liquid media that also serves to inhibit commensals in theclinical specimen. Selenite F broth, tetrathionate broth and alkaline peptone water areused to recover pathogens from fecal specimens.E) Differential media or indicator media: Certain media are designed in such a waythat different bacteria can be recognized on the basis of their colony colour. Variousapproaches include incorporation of dyes, metabolic substrates etc, so that thosebacteria that utilize them appear as differently coloured colonies. Such media are calleddifferential media or indicator media. Examples: MacConkey’s agar, CLED agar, TCBSagar, XLD agar etc.F) Transport media: Clinical specimens must be transported to the laboratoryimmediately after collection to prevent overgrowth of contaminating organisms orcommensals. This can be achieved by using transport media. Such media preventdrying (desiccation) of specimen, maintain the pathogen to commensal ratio and inhibitovergrowth of unwanted bacteria. Some of these media (Stuart’s & Amie’s) are semisolid in consistency. Addition of charcoal serves to neutralize inhibitory factors. CaryBlair medium and Venkatraman Ramakrishnan medium are used to transport fecesfrom suspected cholera patients. Sach’s buffered glycerol saline is used totransport feces from patients suspected to be suffering from bacillary dysentery.G) Anaerobic media: Anaerobic bacteria need special media for growth because theyneed low oxygen content, reduced oxidation–reduction potential and extra nutrients.Media foran aerobes may have to be supplemented with nutrients like hemin andvitamin K. Boiling the medium serves to expel any dissolved oxygen. Addition of 1%glucose, 0.1% thioglycollate, 0.1% ascorbic acid, 0.05% cysteine or red hot iron filingscan render a medium reduced. Robertson cooked meat that is commonly used to growClostridium spps medium contain a 2.5 cm column of bullock heart meat and 15 ml ofnutrient broth. Before use the medium must be boiled in water bath to expel anydissolved oxygen and then sealed with sterile liquid paraffin. Methylene blue or
resazurin is an oxidation-reduction potential indicator that is incorporated in thethioglycollate medium. Under reduced condition, methylene blue is colourless.FOR USE IN FOOD MICROBIOLOGYWhile some media are good for isolation of bacteria in food. The same media cannot be used forthe isolation of fungi. Essentially, microbiological culture media consist of Nitrogen source e.g.protein, amino acid etc. Water source which has to be pure, an energy source in form ofcarbohydrate and peptide and necessary growth factors like mineral salts and group B vitamins.TYPES OF CULTURE MEDIAOn the basis of the essential component micro biological culture media can be grouped as follows; GENERAL-PURPOSE CULTURE MEDIA These are media that provide nutrition for growth of non-fastidious, heterotrophicmicroorganisms, such media include, Nutrient agar, blood agar and plate count agar forbacteria, or malt extract agar and potato/dextrose agar for fungi. These media do notcontain any inhibitory agent however, they may not support the growth of fastidiousorganisms ENRICHMENT CULTURE MEDIA: these are formulated to stimulate the growth ofcertain organism by appropriate selection of condition e.g. Rapaport – vassilliade broth,selenite F. broth, Tetrathionate broth. ELECTIVE CULTURE MEDIAThese groups of media satisfy the minimum nutritional requirement for growth for e.g.Lysine agar. SELECTIVE CULTURE MEDIAThis group of culture media select certain organisms while at the same timeinhibit the growth of others e.g. Salmonella- Shigella medium good for isolationof Salmonella in food, Preston selective medium good for Campylobacter infood. DIAGNOSTIC CULTURE MEDIUMThis type of culture medium uses specific metabolic activity which is associated withthe growth of some organism to produce recognizable changes in the medium for e.g.STARCH agar. SELECTIVE AND DIAGNOSTIC (DIFFERENTIAL)This type of culture medium differentiate one organism relative to all other organismpresent on the culture medium for e.g. on the basis of colour as obtained inMacConkey agar. This medium also utilizes lactose fermentation in the presence of asuitable indicator. On the basis of lactose fermentation some organism are reddish incolour i.e. lactose fermenters. Non-lactose fermenters appear as pale or colourlesscolonies.CULTURING METABOLICALLY INJURED ORGANISMWhen microorganisms are subjected to environmental stresses as in thermal processing many ofthe individual cell are known to undergo metabolic injury which can lead to their not being able to
be isolated on ordinary culture media. In order to be able to isolate these microorganisms it isnecessary to pre-enriched them prior to isolation and for this purpose, it is recommended that nonselective culture media be used. Generally, the use of TSB (Trypticase Soy broth) incubated at 2037ºC for about 1- 24 hours is ideal for isolation of yeast that has undergone sub-lethal heatingprocessing, potato dextrose agar (PDA) at pH 8.0 is recommended for use.FAST METHODS IN USE FOR FOOD MICROBIOLOGYBecause of improvement in biotechnology it is now possible to identify an unknownmicroorganism in food in relatively short period of time.Some of the methods are used at the molecular level and they can also be applied for routine usewhere the economy is buoyant e.g. of these methods include the following:(1) Immunoassay: whereby the organism is fluorescence labeled andcan be identified by colour changes (fluorescence labeling).(2) Other methods(a) Diagnostic kits e.g. for isolation of Staph. aureus kits such as theAPI system and OXI/FERM tubes (entero tubes) are used.(b) Use of monoclonal antibody in ELISA (Enzyme linkedimmunosorbent assay).(3) DNA probes: in the DNA probe the bacteria are applied to a solid support,such as a nitrocellulose membrane filter, by spotting of filtration.Thereafter the organisms are (a) Lysed and disrupted resulting in the release of double strandedDNA. (b) Denatured into single strand DNA that has been separated in form of strands is now (c)fixed to the solid support so that they would not be washed away during the next procedure. Thestrands are now (d) incubated in suitable fluids, after which the appropriate probe is mixed with theDNA on the filter. Unbound protein is washed away, and X-ray film of the preparation can betaken for comparative purposes (analysis). Radioactive colonies will appear as black dust on thefilm.(1) Limulus Lysate assay—this test is specifically useful for endotoxin and as such it isbeing adopted for use in detecting Gram –ve bacteria in food. For this test, aliquot partof the food suspension or any other small amount of the given material is added to thelysate after the preparation is incubated at 37ºc for 1 hour. If there is endotoxin, therewill be Gel formation.(2) Use the Oxi/ferm tubes – based in argnine, nitrogen gas hydrogen sulphide, xylose,AER-DEX, Urea citrate etc.FOOD FUNGILike Bacteria, morphological characters are useful in the study of fungi. By far the easiest way toidentify fungi in food is by using cultural technique on acidified media like – malt extract agar,potato dextrose agar or sabouraud dextrose agar.Food fungi are divided into yeast and mould and the study of these microorganisms arereferred to as FOOD MYCOLOGY.Like bacteria, fungi in food require nutrient, moisture, adequate temp. and atmosphere, aswell as H concentration (pH) for survival in food.Although some fungi are beneficial to man in terms of production of enzyme and bybeing used for food (edible fungi) quite a lot of them are known to spoil food matrices.
TRUE FUNGI (EUMYCETES)Phycomycetes BasidiomycetesMucoralesMucorAscomycetesFungi ImperfectSaccharomycetalesThaminidium SaccharomycesRhizopusHansenulaPicchiaFUNGI ariaYEASTTuberculiaceaeFusarium
Yeasts on their own are larger than bacteria. They are single organism, which can bemicroscopically recognized.(1)They are saprophytic in nature and can be found in dust, soil, and severalother places.(2)Industrially, yeast is important in the production of beer and several otheralcoholic beverages.(3)They are also useful in production of wine and also baking production.(4)They are important in production of proteins fats and vitamins.(5)They are important in production of Enzymes such as amylases.(6)They can be use as food by man and animal.Structurally, in the simplest form, a yeast cell has an outer cell wall made up of complexpolysaccharides and a cell membrane all of which function in the same way as a bacterial cell.MOULDSMacromorphologically, the moulds are composed essentially of multifaceted hyphace(complex collection of hypha referred to as mycelium). These hyphae are thread like structureand serves as sources of nourishment for microorganism.Some mould may be septated (i.e. have septae) while some do not have.IMPORTANCE OF MOULDSGenerally,(1) Moulds are very important in the shelf-life of grains, meats etc that are meant for storage,(2) Some are very pathogenic for man and animal because they produce potent toxins such asaflatoxin, which are very lethal to man and animal – these toxins are referred to asmycotoxin. However, some moulds grow without much problem that is they requiremineral nutrient.(3) Some mould are also important in the production of some food products e.g. cheese e.g.Penicillium.(4) Use in commercial production of proteases and acetic acid e.g. Aspergillus.(5) Use in the production of antibiotics e.g. Penicillin, and conversion of starch to alcohole.g. Rhizopus.(6) Some moulds are very useful in the assay of some essential vitamins.SOME METHOD OF PREVENTING FUNGAL DAMAGEThe following methods are recommended to minimize fungal damage of: (1) Harvest the crop when they are fully matured.(2) Dry the grains as quickly as possible to a suitable moisture content level.(3) Avoid bruises or physical damage to the grains at all stages of handling the grains.(4) It is essential to check the moisture content before storage, particularly if they are meantto be stored for a long time.(5) Avoid storing warm grain as this may retain heat and leads to mouldiness.(6) Ensure that all the storage houses are in good shape particularly if the roofs are leaking tobe mended.(7) In storing the produce, the bag should be stored always away from the wall of thestorehouse.
(8) Ensure good ventilation and even temp. in the store house. If polyethene bags are to beused for storing purposes they should be resistant to insect damage and as much aspossible, contamination by insects, rodents and flies should be minimized.It is recommended that loading and off-loading of produce during the raining season should becarefully done. In fact if vehicles are to be used strong tarpaulin should be used to cover thevehicle. However, it is generally advisable not to load or unload during the raining season.Factors that Influence Microbial GrowthMany factors must be evaluated for each specific food when making decisions on whether itneeds time/temperature control for safety. These can be divided into intrinsic and extrinsicfactors. Intrinsic factors are those that are characteristic of the food itself; extrinsic factors arethose that refer to the environment surrounding the food. The need for time/temperature controlis primarily determined by 1) the potential for contamination with pathogenic microorganisms ofconcern (including processing influences), and 2) the potential for su
Food Microbiology Brief history of Food Microbiology. Flora and sources of microorganisms in food. Methods of detection and . COLI/API system all of which are used for identification of unknown organisms. . This is t
taught MCB 200 (2013), MCB 210 (2014), and MCB 230 (2014). These courses laid out the foundation for my critical thinking and independent researching abilities. I also want to thank my students while I was teaching as a graduate student instructor in Fall 2014 (MCB 32L), Spring 2016 (MCB 102), and Fall 2018 (MCB 132).
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