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CHAPTER 9 CONTROL OF MICROBIAL GROWTH. Terminology of Microbial Control Sepsis/ Asepsis –Aseptic techniques Sterilization Commercial Sterilization Sanitization.

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Presentation on theme: "CHAPTER 9 CONTROL OF MICROBIAL GROWTH. Terminology of Microbial Control Sepsis/ Asepsis –Aseptic techniques Sterilization Commercial Sterilization Sanitization."— Presentation transcript:

1 CHAPTER 9 CONTROL OF MICROBIAL GROWTH

2 Terminology of Microbial Control Sepsis/ Asepsis –Aseptic techniques Sterilization Commercial Sterilization Sanitization

3 Antisepsis vs Disinfection –Biocide vs Biostatic Degerming Chemotherapy

4 Factors that influence the effectiveness of anti- microbial procedures: 1.microbial characteristics 2.number of microbes –Decimal reduction time (D value) 3.environmental influences 4.time of exposure 5.concentration or intensity of treatment

5

6 1.Heat (moist & dry) 2.Filtration 3.Low temperature 4.High pressure 5.Desiccation & Osmotic pressure 6.Radiation Physical or Mechanical Methods

7 1.Heat Moist Heat –Boiling kills most vegetative forms in 10 min –Autoclave – steam under pressure –Sterilization - 15 psi, 121 O C for 15 min –Pasteurization –Standard methods do not sterilize –higher temp, shorter exposure time Dry heat Incineration Flaming dry heat sterilization Requires higher temp and longer exposure 170°C for 2 hours is equivalent to autoclaving

8 2. Low Temperatures –Slows metabolic rate –Freezing forms ice crystals that can damage cells –Slow freezing then thawing does most damage 3. Filtration –Mechanical sterilization of heat-sensitive material –HEPA 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 foods –Preserves flavor, taste, appearance, and nutritional value

10 5.Desiccation –Resistance varies by species can’t reproduce or grow, but may remain viable –Osmotic pressure create a hypertonic environment; dehydrates cells Preserved fruits (sugar), cured meat (salt), and pickles (salt)

11 6. Radiation depends on wavelength, intensity and duration Ionizing vs non-ionizing Sterilization of food products and disposable medical equipment; water treatment

12 Evaluating Anti-microbial Compounds Phenol coefficient test Use-dilution test –Current industry standard

13 Disk-Diffusion Method

14 Types of Anti-microbial Chemicals –Phenol (carbolic acid) Rarely used, irritating qualities and bad odor Penolic compounds more common Disinfect for surfaces (Lysol) and antiseptic (antimicrobial soaps and lotions) –Halogens Iodine – antiseptic or disinfectant –May be available as a tincture or iodophore Chlorine - disinfectant (water treatment)

15 –Alcohols Affect vegetative forms of bacteria, fungi, and enveloped viruses ethanol and isopropanol - degermer (hand sanitizer) and disinfectant 70% solution typically is most effective –Heavy metals Silver; mercury; copper antiseptic, algicide, mildew control paints, placed in newborn’s eyes to prevent spread of gonorrhea

16 –Surfactants Soap –Emulsification; degerming –Least effective of all chemical methods Anionic Detergents –Commercial sanitizers Cationic Detergents –disinfectant and antiseptic

17 –Peroxygens Disinfectants Ozone – supplements chlorine in water treatment Hydrogen peroxide – good disinfectant not antiseptic –Where do the bubbles come from? –Aldehydes Disinfectant and preservative Formaldehyde – formalin –Irritating and carcinogenic Glutaraldehyde –Liquid chemical sterilant

18 –Biguanides Chlorohexidine most effect class antiseptic in lotions, soaps and impregnated into surgical meshes and plastics –Ethylene oxide Gaseous chemo-sterilizer hours exposure kills all microbes Useful for heat sensitive materials

19 –Food preservatives Organic acids – Sodium benzoate, Sorbic acid –Inhibit mold growth in acidic foods Calcium propionate - fungicide used in bread –Inhibit mold growth Nitrates- added to many meat products –prevents germination and growth of botulism endospores –preserves the pleasing red color ????

20 –Antibiotics Nisin- added to cheese to inhibit growth of endospore formers Natamycin – antifungal used in food (mostly cheese) Why should medical antibiotics not be used in food preservation?


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