CONTROL OF MICROBIAL GROWTH CHAPTER 9 CONTROL OF MICROBIAL GROWTH

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

Antisepsis vs Disinfection Biocide vs Biostatic Degerming Chemotherapy

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

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

Heat Moist Heat Dry 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

2. Low Temperatures 3. Filtration 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

4. High Pressure Up to 130,000 psi Endospores are resistant Commercially pasteurize foods Preserves flavor, taste, appearance, and nutritional value

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)

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

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

Disk-Diffusion Method

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)

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

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

Peroxygens Aldehydes 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

Biguanides Ethylene oxide 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

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 ????

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?