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Food Microbiological principles FST 241
 

Food Microbiological principles FST 241

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Basic microbiology info for food preservation

Basic microbiology info for food preservation

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    Food Microbiological principles FST 241 Food Microbiological principles FST 241 Presentation Transcript

    • Microbiological Principles of Food Preservation
    • Types of Microbes on Food
      • Bacteria – one celled, Procaryotic
      • Molds – Threadlike Fungi
      • Yeasts – Usually creamy Fungi
    • Other microorganisms of concern
      • Viruses – protein packet of genes
      • Protozoa –Complex cell - Eucaryotic
      • Do not multiply in foods
      • Contaminate food
        • Humans
        • Contaminated water
    • Bacterial Cells?
      • Contain Genes that Program the Cell and Help It Survive
      • Reproduction
        • Binary Fission – One Cells Splits in Two
        • 1 cell > 65,000 cells in ~4 hours
      • Cause Illness or Disease - Pathogens
      • Cause Deterioration of Foods – Spoilage
      • Useful - fermentation
    • Some Microorganisms Cause Disease
      • Microorganisms that cause disease referred to as pathogens
      • Few of the known microorganisms are harmful to humans
      • Many diseases can be transmitted from person to person or from animals to humans
      • Very few transmitted via foods
    • Some Microorganisms Cause Disease
      • Majority of bacterial foodborne illnesses are caused few microorganisms
        • Salmonella
        • Campylobacter
        • Shigella
        • Clostridium perfringens
        • Staphylococcus aureus
        • Listeria monocytogenes
        • Clostridium botulinum
    • Pathogenic Microorganisms and toxins
      • http://www.fda.gov/Food/FoodSafety/FoodborneIllness/FoodborneIllnessFoodbornePathogensNaturalToxins/BadBugBook/default.htm
    • Food Spoilage and Food Safety
      • Not the Same!
      • Reducing spoilage can actually increase the risk of a harmful bacterium being present
      • Both Preservation and Safety must be ensured by the processor.
      • Processors use the “hurdles” concept to preserve foods and create safe foods.
    • Useful Functions of Microorganisms
      • Food Fermentations
        • Bread, cheese, wine, beer, sauerkraut, sausages, and other fermented foods
      • Enzymes, antibiotics
      • Degrade organic matter
    • Bacteria
      • The most important and troublesome microorganisms for the food processor
      • Bacteria are single-celled living bodies so small that individually they can be seen only with the aid of a powerful microscope
    • Bacteria
      • Bacteria have several shapes or forms
        • Spherical called “cocci”
        • Rod-shaped called “rods”
    •  
    • Reproduction of Bacterial Cells
      • Bacteria reproduce by division
        • “ Fission”
      • Called “growth”
      • Cells in the active stage of growth and metabolism are referred to as vegetative cells
    • Reproduction of Bacterial Cells
      • Under favorable conditions, each cell divides on average about once every 15 or 30 minutes
    • Growth of Microorganisms
    • Molds
      • Multicellular organisms
      • Form tubular filaments or “mycelia”
        • Branched
      • Reproduction
        • Fruiting bodies or spores
        • On aerial structures
      • Larger than bacteria
      • Longer than yeasts
    • Molds
      • Widely distributed in nature
        • Soil and in the dust
      • Will grow on almost any food or substance
        • Pastes, paper, plastics, paint
      • Tolerant to cold
    • Molds
      • Little heat resistance
      • Require oxygen to grow
        • No growth in canned foods unless
          • Air remaining in container
          • Loss of vacuum
    • Yeasts
      • Single cell microscopic living bodies
      • Often oval or egg-shaped
      • Smaller than molds but larger than bacteria
      • Reproduce mainly by budding
    • Budding
    • Yeasts
      • Widely found in nature
      • Often associated with liquid foods containing sugars and acids
      • More tolerant of cold than of heat
        • Most yeast are destroyed by heating to 170F
    • Intrinsic and Extrinsic Food Parameters Affecting Safety & Spoilage “ Hurdles”
      • Intrinsic (inside the food)
        • pH
        • Moisture
        • Oxidation-Reduction Potential Inside Food
        • Natural Antimicrobial Constituents
        • Biological Structures & Natural Microflora
      • Extrinsic (environment around the food)
        • Temperature
        • Relative Humidity
        • Presence of Gases or Oxygen
        • Antimicrobials or Added Microorganisms
    • Preferred Conditions for Bacterial Growth
      • F ood: Carbs, Protein, Fat
      • A cid Range pH 4.6 to 9
      • T emperature above 4C (40 F)
      • T ime Minimum 2 hours
      • O xygen Range varies by microbe
      • M oisture above 0.85 A w
    • What Microorganisms Need to Grow
      • Water
      • Source of Energy
      • Source of Nitrogen
      • Vitamins/Growth Factors
      • Minerals
    • Oxygen Requirements
      • Require oxygen or air
        • Aerobes
      • Free oxygen prevents growth
        • Anaerobes
      • Majority of bacteria neither strict aerobes nor strict anaerobes
        • Facultative Anaerobes
    • Water activity of some common foods
      • Most fresh foods > 0.95
      • Liverwurst 0.96
      • Cheese Spread 0.95
      • Caviar 0.92
      • Fudge Sauce 0.83
      • Semi-moist Pet Food 0.83
      • Salami 0.82
      • Soy Sauce 0.80
      • Peanut Butter – 15% total moisture 0.70
      • Dry Milk – 8% total moisture 0.70
    • pH
      • pH is a measure of acidity
      • pH = -log of the Hydrogen Ion Concentration
      • Major Control Point for Bacteria
      • Major Impact on Food Quality
      • Classification of Foods: Acid, Low-Acid, Alkaline
    • pH Ranges for Food pH 7.0 Neutral pH 0 pH 14 pH 2 pH 3.5 pH 9 pH 4.6 pH 5.5 pH 10 Limes Fruits & Berries Veggies Melons Meats, Milk Bleach Solutions Bacteria Grow
    • Comparison of Growth Requirements Organism pH Range Water Activity Requires Oxygen? Bacteria 4.4 to 9.8 Aw>0.85 Some- It Varies Yeasts 1 to 11 Aw>0.60 Not Usually Molds 1-12 Aw>0.60 Yes
    • Temperature of Growth Classification psychrotroph
    • Classification Optimum Temperature Psychrotroph Mesophiles Thermophiles 58ºF to 68ºF (14ºC to 20ºC) 86ºF to 98ºF (30ºC to 37ºC) 122ºF to 150ºF (50ºC to 66ºC)
    • Sporeforming and Non-Sporeforming Bacteria
      • Most bacteria exist only as vegetative cells
        • All cocci and some rods
        • NON-SPOREFORMERS
      • Some groups of rod-shaped bacteria produce spores
        • SPOREFORMERS
        • Exist as both vegetative cell and spores
    •  
    • Sporeforming and Non-Sporeforming Bacteria
      • Bacterial spores
        • Dormant stage in normal growth cycle
        • Can germinate and produce new vegetative cell
        • Ability to survive a wide range of unfavorable conditions
      • Spores in molds and yeasts
        • Generally not resistant
    • Vegetative Cell Vegetative Cell with Spore Spore 3 Microscopic Forms of a Sporeformer Sensitive Resistant
    • Resistance of Spores to Environment
      • In general, bacterial spores are extremely resistant to heat, cold and chemical agents
        • Survive in boiling water > 16 hours
    • Temperature Requirements
      • Every microorganisms has an optimum (most favorable) temperature range
      • Microorganisms grouped to indicate their relationships to temperature
    • The Psychrotrophic Group
      • Psychrotrophs ( “psychro” for cold and “trophs” for growing)
        • Optimum of 58F-68F
        • Grow slowly on food at refrigerator temperatures 40F
        • Primarily spoilage microorganisms
        • Few pathogens
    • The Mesophilic Group
      • Mesophiles ( “meso” for middle and “phile” for love)
        • Optimum 86F-98F
        • All microorganisms that affect food safety can grow in this temperature range
        • Clostridium botulinum is a mesophile
    • The Thermophilic Group
      • Thermophiles ( “thermo” for heat, “phile” for love)
      • Many are sporeforming bacteria
      • Obligate thermophiles
        • Spores will not germinate and grow below 122F
      • Facultative thermophiles
        • Growth occurs at 122F to 150F
    • The Thermophilic Group
      • Spores of these bacteria are so heat-resistant that they can survive for more than 60 minutes at temperatures of 250F
      • Thermophilic bacteria are not pathogenic and do not affect food safety