Presentation on theme: "CONTROL OF MICROBIAL GROWTH"— Presentation transcript:
1 CONTROL OF MICROBIAL GROWTH CHAPTER 9CONTROL OF MICROBIAL GROWTH
2 Terminology of Microbial Control Sepsis/ AsepsisAseptic techniquesSterilizationCommercial SterilizationSanitization
3 Antisepsis vs Disinfection Biocide vs BiostaticDegermingChemotherapy
4 Factors that influence the effectiveness of anti-microbial procedures: microbial characteristicsnumber of microbesDecimal reduction time (D value)environmental influencestime of exposureconcentration or intensity of treatment
7 Heat Moist Heat Dry heat Boiling kills most vegetative forms in 10 min Autoclave – steam under pressureSterilization - 15 psi, 121OC for 15 minPasteurizationStandard methods do not sterilizehigher temp, shorter exposure timeDry heatIncinerationFlamingdry heat sterilizationRequires higher temp and longer exposure170°C for 2 hours is equivalent to autoclaving
8 2. Low Temperatures 3. Filtration Slows metabolic rate Freezing forms ice crystals that can damage cellsSlow freezing then thawing does most damage3. FiltrationMechanical sterilization of heat-sensitive materialHEPA filters (high efficiency particulate air filters)Membrane filters have pores as small as 0.01 microns
9 4. High Pressure Up to 130,000 psi Endospores are resistant Commercially pasteurize foodsPreserves flavor, taste, appearance, and nutritional value
10 5. Desiccation Resistance varies by species can’t reproduce or grow, but may remain viableOsmotic pressurecreate a hypertonic environment; dehydrates cellsPreserved fruits (sugar), cured meat (salt), and pickles (salt)
11 6. Radiation depends on wavelength, intensity and duration Ionizing vs non-ionizingSterilization of food products and disposable medical equipment; water treatment
12 Evaluating Anti-microbial Compounds Phenol coefficient testUse-dilution testCurrent industry standard
14 Types of Anti-microbial Chemicals Phenol (carbolic acid)Rarely used, irritating qualities and bad odorPenolic compounds more commonDisinfect for surfaces (Lysol) and antiseptic (antimicrobial soaps and lotions)HalogensIodine – antiseptic or disinfectantMay be available as a tincture or iodophoreChlorine - disinfectant (water treatment)
15 AlcoholsAffect vegetative forms of bacteria, fungi, and enveloped virusesethanol and isopropanol - degermer (hand sanitizer) and disinfectant70% solution typically is most effectiveHeavy metalsSilver; mercury; copperantiseptic, algicide, mildew control paints, placed in newborn’s eyes to prevent spread of gonorrhea
16 Surfactants Soap Emulsification; degerming Least effective of all chemical methodsAnionic DetergentsCommercial sanitizersCationic Detergentsdisinfectant and antiseptic
17 Peroxygens Aldehydes Disinfectants Ozone – supplements chlorine in water treatmentHydrogen peroxide – good disinfectant not antisepticWhere do the bubbles come from?AldehydesDisinfectant and preservativeFormaldehyde – formalinIrritating and carcinogenicGlutaraldehydeLiquid chemical sterilant
18 Biguanides Ethylene oxide Chlorohexidine most effect class antiseptic in lotions, soaps and impregnated into surgical meshes and plasticsEthylene oxideGaseous chemo-sterilizer4 -18 hours exposure kills all microbesUseful for heat sensitive materials
19 Food preservatives Organic acids – Sodium benzoate, Sorbic acid Inhibit mold growth in acidic foodsCalcium propionate - fungicide used in breadInhibit mold growthNitrates- added to many meat productsprevents germination and growth of botulism endosporespreserves the pleasing red color ????
20 AntibioticsNisin- added to cheese to inhibit growth of endospore formersNatamycin – antifungal used in food (mostly cheese)Why should medical antibiotics not be used in food preservation?
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