BIOLOGY 2250

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BIOLOGY 2250

• MICROBIAL GROWTH and ITS CONTROL

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BIOLOGY 2250

• PART 1. MICROBIAL GROWTH

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Requirements for Growth

• Physical Requirements Temperature, pH, Osmotic
  Pressure
• Chemical Requirements Carbon, Nitrogen, Sulfur,
  Phosphorous, Trace Elements, Oxygen, Organic
  Growth Factors

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Temperature Requirements

• Mesophiles
• Psychrophiles
• Psychotrophs
• Thermophiles
• Hyperthermophiles

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TEMPERATURE OF FOODS
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OSMOTIC PRESSURE
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OXYGEN REQUIREMENTS
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BINARY FISSION

• Little increase in size
• Growth in numbers to form colonies on an agar
  plate

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How about these numbers!
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BACTERIAL GROWTH
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GROWTH PHASES
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BIOLOGY 2250

• PART 2. CONTROL OF MICROBES

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TERMINOLOGY
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MICROBIAL DEATH
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Types of Cell Damage

• Alterations of Plasma Membrane
• Damage to Proteins and Nucleic Acids

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PHYSICAL METHODS OF CONTROL

• Moist heat
• Dry heat
• Filtration
• High pressure
• Desiccation
• Osmotic pressure
• radiation

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Moist Heat

• Autoclave

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Principle of Autoclave

• Adjust your recipe to your altitude!

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Dry Heat

• Oven
• Bunsen burner flame

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FILTRATION

• Membrane filters have different pore sizes, e.g.
  0.45 µs

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High Pressures

• Fruit Juices

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Desicattion

• Freeze Dried Foods
• Dried Meats
• Dried Fruits

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Osmotic Pressure

• Salting
• Pickling -

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RADIATION

• Ionizing cobalt, gamma rays
• Nonionizing UV light
• Microwave

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CHEMICAL CONTROL
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CHEMICAL CONTROL