Module 6: Control of Microbial Growth

• sterilization: kills all viable organisms including endospores
• disinfection: remove all pathogens from surfaces
• antisepsis: remove all pathogens from living tissue
• sanitation: remove pathogens to safe level
• physical antimicrobial control: temperature, radiation sterilization, drying, and filter sterilization
• moist heat sterilization (autoclave) is more effective than dry heat (oven)
• refrigeration stops most microbes from growing
• freezing can preserve microbes
• what do cryoprotectants do?

  inhibit ice crystal formation
• pasteurization: heat to kill microbes without altering food
• original method of pasteurization was batch, now use faster method of flash pasteurization
• what type of pasteurization allows you to store food at room temperature?

  ultra high temperature sterilization
• radiation sterilization: ionizing radiation (gamma and x rays) kills microbes by damaging DNA and proteins
• UV rays only sterilize surfaces
• drying targets microbes that require water activity
• direct drying: evaporation or heating
• indirect drying: adding high concentration of solutes (salt and sugar)
• filter sterilization: small pores prevent microbes from passing through
• what is a benefit of filter sterilization?

  avoids heat for sensitive liquids
• depth filters: diatoms or fibrous
• membrane filters: cellulose
• nucleopore membranes: very small pores
• syringe filters are used for small volumes and vacuum filters are used for large volumes
• what are considerations for chemical antimicrobial control?

  • type of microbe (chemical resistance)
  • presence of organic matter to absorb toxicity
  • toxicity to non target organisms
• acid growth control(pickling): lower ph so microbes can't grow, produced by bacteria (fermentation)
• alcohol growth control: produced by yeasts (fermentation)
• sugar and salt growth control: affects osmotic conditions
• chemical biocides: nonspecific toxic chemicals. can damage many organisms
• how do chemical biocides impact target organisms?

  • chemically modify or denature DNA and proteins
  • dissolve or disrupt membranes
• antibiotics: narrow range chemicals selectively target 1 type of organism
• antibiotics are produced by bacteria, fungi, or plants