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CHAPTER 7

CHAPTER 7. CONTROL OF MICROBIAL GROWTH. Terminology of Microbial Control. Sepsis Asepsis Aseptic techniques Sterilization Commercial Sterilization Sanitization. Antisepsis vs Disinfection Biocide Biostatic Degerming Chemotherapy.

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CHAPTER 7

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  1. CHAPTER 7 CONTROL OF MICROBIAL GROWTH

  2. Terminology of Microbial Control • Sepsis • Asepsis • Aseptic techniques • Sterilization • Commercial Sterilization • Sanitization

  3. Antisepsis vs Disinfection • Biocide • Biostatic • Degerming • Chemotherapy

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

  5. Physical or Mechanical Methods • Heat (moist & dry) • Filtration • Low temperature • High pressure • Desiccation & Osmotic pressure • Radiation

  6. Heat • Moist Heat • Boiling kills most vegetative forms in 10 min • Autoclave – steam under pressure • Sterilization - 15 psi, 121OC 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

  7. 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

  8. 4. High Pressure • Up to 130,000 psi • Endospores are resistant • Commercially pasteurize foods • Used to sterilize liquid food products while preserving flavor, taste, appearance, and nutritional value

  9. 5. Desiccation • Resistance varies by species • can’t reproduce or grow, but may remain viable • lyophilization • Freeze-drying – freeze then dry in a vacuum Osmotic pressure • create a hypertonic environment; dehydrates cells • Preserved fruits (sugar), cured meat (salt), and pickles (salt)

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

  11. Evaluating Anti-microbial Compounds • Phenol coefficient test • Use-dilution test • Current industry standard

  12. Disk-Diffusion Method

  13. Types of Anti-microbial Chemicals • Phenol (carbolic acid) • Rarely used, irritating qualities and bad odor • Penolic compounds • 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)

  14. 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

  15. Surfactants • Soap • Emulsification; degerming • Least effective of all chemical methods • Anionic Detergents • Commercial sanitizers • Cationic Detergents • disinfectant and antiseptic • Quaternary ammonium compounds (Quats) • most widely used cationic detergents • Pseudomonas resistant

  16. 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

  17. Biguanides • Chlorohexidine most effect class • antiseptic in lotions, soaps and impregnated into surgical meshes and plastics • Ethylene oxide • Gaseous chemo-sterilizer • 4 -18 hours exposure kills all microbes • Useful for heat sensitive materials

  18. Food preservatives • Organic acids – Sodium benzoate, Sorbic acid • Prevent molds from growing in acidic foods • Calcium propionate - fungicide used in bread • Inhibit mold growth by interfering with plasma membrane • Nitrates- added to many meat products • prevents germination and growth of botulism endospores • preserves the pleasing red color

  19. 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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