CALS Farm and Industry Short Course Program: Farm Microbiology: Lecture Outlines

SECTION 5.
Food Microbiology
including the specialized areas of Silage and Dairy Microbiology

PART ONE – GENERAL PRINCIPLES OF FOOD MICROBIOLOGY

1. Importance of microorganisms in foods.
   
   
   1. Spoilage of foods.
      
      
   2. Production of some foods.
      
      
   3. Food-borne illnesses.
      
      
   4. Indicator organisms.
      
      
2. Food spoilage.
   
   
   1. Proteins, fats and carbohydrates.
      
      
   2. Foods containing very high levels of sugar.
      
      
   3. Dry foods.
      
      
3. Food preservation – i.e., prevention of spoilage.
   
   
   1. Principles.
      
      
      1. Keep microorganisms out.
         
      2. Inhibit microbial growth and activity.
         
      3. Removal of microorganisms.
         
      4. Kill microorganisms.
         
      5. Inactivate enzymes in foods.
         
         
   2. Methods to control microbial growth in foods.
      
      
      1. Keeping organisms out.
         
         
      2. Removing organisms.
         
         
      3. Low temperatures.
         
         
      4. High temperatures.
         
         
      5. Drying.
         
         
      6. Inhibitory chemicals. (See review here.)
         
         
         1. Inherent to the food product itself.
            
            
         2. Addition to the recipe.
            
            
         3. Addition by microorganisms.
            
            
      7. Ultraviolet and ionizing irradiation.
         
         
      8. Combination of methods and the Barrier Concept.
         
         
4. Food-borne Illnesses.
   
   
   1. The Bad Bug Book.
      
      
   2. Definitions of food poisoning and food infection.
      
      
      1. Food poisoning.
         
         
      2. Food infection.
         
         
   3. Food poisoning (food intoxication).
      
      
      1. Botulism.
         
         
         1. The organism: Clostridium botulinum.
            
            
         2. Types of botulism.
            
            
         3. Conditions for toxin production.
            
            
         4. The disease.
            
            
         5. Prevention of outbreaks.
            
            
      2. Staphylococcal food poisoning.
         
         
         1. The organism: Staphylococcus aureus.
            
            
         2. Conditions for toxin production.
            
            
         3. The disease.
            
            
         4. Prevention of outbreaks.
            
            
      3. Fungal toxins (mycotoxins).
         
         
         1. Aflatoxins.
            
            
         2. Mushroom toxins.
            
            
   4. Food infections.
      
      
      1. Salmonella infections (human salmonellosis and other diseases).
         
         
      2. E. coli infections.
         
         
      3. Listeriosis.
         
         
      4. Infant botulism.
         
         
      5. Hepatitis.
         
         
      6. Trichinosis.
         
         
5. Production of foods with the aid of microorganisms. (Silage and fermented dairy products are considered in separate sections below.)
   
   
   1. Use of starter cultures vs. wild fermentation.
      
      
   2. Bread.
      
      
      1. Functions of yeast.
         
         
      2. Sources of flavor.
         
         
      3. Spoilage.
         
         
   3. Alcoholic beverages.
      
      
   4. Vinegar.
      
      
   5. Fermented sausage.
      
      
      1. Manufacture.
         
         
      2. Fermentation.
         
         
         1. Use of starter culture – Lactobacillus or Pediococcus.
            
            
         2. Multiple importance of acid.
            
            
      3. Defects.
         
         
         1. If too much nitrite.
            
            
         2. If not enough fermentation.
            
            
   6. Sauerkraut.
      
      
      1. Process involves addition or creation of inhibitory/preservative agents.
         
         
      2. Manufacture.
         
         
      3. Obtaining anaerobic conditions.
         
         
      4. Fermentation – involves "floral succession."
         
         
         1. Coliforms (in enteric bacteria group).
            
            
         2. Leuconostoc (in lactic acid bacteria group).
            
            
         3. Lactobacillus (also in lactic acid bacteria group).
            
            
      5. Defects.
         
         

PART TWO – SILAGE MICROBIOLOGY

1. Phases of the fermentation/manufacturing process.
   
   
   1. Overview.
      
      
   2. Aerobic phase.
      
      
   3. Lag phase.
      
      
   4. Acetic acid phase.
      
      
   5. Lactic acid phase.
      
      
   6. Stable phase.
      
      
2. Defects.
   
   
   1. Due to too much oxygen.
      
      
   2. Due to silage being too wet.
      
      
   3. Due to excess contamination by soil.
      
      
3. Addition of NPN (non-protein nitrogen).
   
   
   1. At beginning of process.
      
      
   2. When fed to livestock.
      
      

PART THREE – DAIRY MICROBIOLOGY

1. Milk.
   
   
   1. Definition of milk.
      
      
   2. Average gross composition of milk.
      
      
      1. Water.
         
         
      2. Fat.
         
         
      3. Lactose.
         
         
      4. Proteins.
         
         
      5. Ash.
         
         
      6. Minor constituents.
         
         
   3. Nutritional value.
      
      
   4. Keeping quality (shelf-life).
      
      
2. Sources of microorganisms in milk.
   
   
   1. Interior of the udder.
      
      
   2. Exterior of the udder.
      
      
   3. Coat of the cow.
      
      
   4. Utensils.
      
      
   5. Air.
      
      
   6. Flies and other insects.
      
      
   7. Humans.
      
      
3. Changes in milk resulting from microbial growth.
   
   
   1. What happens if milk is allowed to spoil – a "floral succession."
      
      
      1. Streptococcus and Lactobacillus.
         
         
      2. Yeast and molds.
         
         
      3. Bacillus.
         
         
   2. Fermentation.
      
      
   3. Proteolysis.
      
      
   4. Alkali production.
      
      
   5. Ropiness or sliminess.
      
      
   6. Changes in butterfat.
      
      
   7. Flavor and aroma changes.
      
      
   8. Color changes – may involve Pseudomonas, Serratia, Chromobacterium.
      
      
4. Procedures to reduce or minimize changes in milk.
   
   
   1. Asepsis.
      
      
   2. Use of low temperatures.
      
      
   3. Use of heat.
      
      
      1. Pasteurization.
         
         
      2. Boiling and steam under pressure (autoclaving).
         
         
   4. Other methods of preservation.
      
      
      1. Condensing.
         
         
      2. Drying.
         
         
      3. Adding preservatives.
         
         
      4. Preservation by fermentation.
         
         
5. Determining bacteriological quality of milk.
   
   
   1. Standard plate count.
      
      
   2. Coliform count.
      
      
   3. Direct microscopic count.
      
      
   4. Dye reduction tests (methylene blue and resazurin).
      
      
   5. Tests for abnormal (mastitic) milk.
      
      
      1. The California and Wisconsin Mastitis Tests and the Modified Whiteside Test.
         
         
      2. Catalase test.
         
         
6. Presence of foreign chemicals in milk.
   
   
   1. Antibiotics.
      
      
      1. Sources of antibiotics in milk.
         
         
      2. Detrimental effects of antibiotics in milk.
         
         
      3. How can the problem be minimized?
         
         
   2. Pesticides of the chlorinated hydrocarbon type.
      
      
      1. Sources of pesticides in milk.
         
         
      2. Where pesticides accumulate.
         
         
      3. Detrimental effects of pesticide residues.
         
         
      4. How can the problem be minimized?
         
         
7. Examples of cultured dairy products.
   
   
   1. Yogurt.
      
      
      1. Preparation of the milk.
         
         
      2. The fermentation process – employing starter cultures such as Streptococcus thermophilus, Lactobacillus bulgaricus, Lactobacillus acidophilus.
         
         
   2. Cheeses.
      
      
      1. Solidification of protein accomplished by:
         
         
         1. Acid from lactic acid fermentation.
            
            
         2. Addition of coagulant (rennet).
            
            
      2. Variety of cheeses due to:
         
         
         1. Variety of organisms used for fermentation and/or flavoring.
            
            
         2. Sources of milk.
            
            
         3. Different aging processes.
            
            
      3. Examples.
         
         
         1. Swiss cheese (with addition of Propionibacterium).
            
            
         2. Blue cheese (with addition of Penicillium roquefortii).
            
            
8. Probiotics.
   
   
   
   

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Page last modified on 3/7/05 at 2:30 PM, CST. John Lindquist, Dept. of Bacteriology, University of Wisconsin – Madison