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MICROBIOLOGY - ALCAMO

MICROBIOLOGY - ALCAMO. CHAPTER 24: MICROBIOLOGY OF FOODS. Case of the Patty Melt. The 3 rd largest outbreak of botulism in our country occurred in October, 1983, at the Skewer Inn, Peoria Illinois Between October 14 th and 16 th , 36 people began to feel the paralyzing signs of botulism

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MICROBIOLOGY - ALCAMO

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  1. MICROBIOLOGY - ALCAMO CHAPTER 24: MICROBIOLOGY OF FOODS

  2. Case of the Patty Melt • The 3rd largest outbreak of botulism in our country occurred in October, 1983, at the Skewer Inn, Peoria Illinois • Between October 14th and 16th, 36 people began to feel the paralyzing signs of botulism • Blurred vision, difficulty swallowing and chewing, and labored breathing • All had to be hospitalized, and all but one person recovered

  3. Case of the Patty Melt • Investigators from the CDC came to investigate • They identified the patty melt as the common food eaten by the sick people • But, they had to determine what part of the sandwich was the culprit • They were able to isolate Clostridiumbotulinum spores from fresh onions

  4. Case of the Patty Melt • Once sautéed, the onions were left uncovered on a warm stove for hours • The onions had not been reheated before serving • Spores had germinated in the anaerobic mounds of warm onions and deposited their toxins

  5. Why Did It Happen?? • Most foods (even cooked foods) provide excellent conditions for growth of MO’s • There is plenty of organic matter, water content is high, and the pH is usually neutral • We will be talking about types of organisms that contaminate food, the consequences of them, and how to prevent them

  6. Food Spoilage • Has been a problem since humans started producing more food than could be eaten in one meal • Marco Polo explored new trade routes to get spices to improve the smell and taste of spoiled food • Refrigeration and canning were not yet invented

  7. Food Spoilage • Food is considered spoiled if it is altered from its expected form • Usually it will have an unpleasant appearance, aroma, and taste • Sometimes you can’t tell if there aren’t enough MO’s or they deposit a toxin • Consumption of toxins or MO’s can cause a variety of food poisonings and infections

  8. ENTRY OF MO’S TO FOOD • Air – MO’s fall onto fruit and vegetables and penetrate through a break in the skin or rind • Soil – crops carry soilborne bacteria into processing plants • Rodents and arthropods – transport MO’s on their feet and body parts as they are around food

  9. ENTRY OF MO’S TO FOOD • Human handling – processing and storage • Careless butcher – can contaminate meat with bacteria from an animal’s intestines • Raw fruits and vegetables – salad bars

  10. Factors Affecting Growth of MO’s Water: • Food must be moist for MO’s to grow (water content of 18-20%) • MO’s do not grow in foods like dried beans, rice, and flour because of the low water content

  11. Factors Affecting Growth of MO’s pH: • Most foods are neutral to slightly acidic • Many bacteria grow well under these conditions • If food pH is below 5.0 molds like to grow • Citrus foods are rarely spoiled by bacteria – usually mold

  12. Factors Affecting Growth of MO’s Physical Structure: • It may be physically easier for the MO to penetrate into the food • MO’s have a harder time penetrating steak than hamburger meat • Mo’s can exist within the loosely packed meat

  13. Factors Affecting Growth of MO’s Chemical Composition of Food: • MO’s that metabolize carbohydrates – found on fruits • MO’s that metabolize protein – found on meats • Presence of certain vitamins might encourage MO’s to grow and absence of vitamins may discourage growth

  14. Factors Affecting Growth of MO’s Oxygen: • Vacuum-sealed cans (all oxygen removed) do not support the growth of aerobic bacteria • Vegetables and bakery products do not support the growth of anaerobes

  15. Factors Affecting Growth of MO’s Temperature: • The refrigerator is too cold for the growth of human pathogens • A hot warehouse storeroom would encourage the growth of these

  16. Chemistry of Spoilage • Spoilage often due to naturally occurring chemistry of contaminating MO • Yeasts – live in apple juice and convert sugar to ethyl alcohol • Certain bacteria – break down protein into bad-smelling end products (rotten egg) • Carbohydrates can break down into • acid – sour food • gas – causes sealed cans to swell

  17. Chemistry of Spoilage • In General: • Bacteria - spoil fresh foods • Fungi - spoil breads, fruits, and dried foods

  18. Food Industry Divides Food By Its Properties Highly Perishable – Spoil rapidly Examples: Poultry, eggs, meats, most vegetables and fruits, dairy products

  19. Highly Perishable • Meats and Fish – muscle tissue of animals usually sterile • Spoilage usually occurs during handling, processing, packaging and storage • Processed meats – even greater hazard because they are handled so often • Organ meats – less compact tissue and spoil more quickly

  20. Highly Perishable • Poultry and Eggs – contamination is usually from MO’s that have infected the bird • Salmonella causes disease in turkeys and chickens – passed on to consumers via poultry and egg products • Eggs are normally sterile, but shell can get penetrated by bacteria after a few hours

  21. Food Industry Divides Food By Its Properties Semiperishable – Spoil less quickly Examples: nutmeats, potatoes, and some apples

  22. Food Industry Divides Food By Its Properties Nonperishable – Not subject to rapid spoiling Cereals, rice, dried beans, macaroni products, flour and sugar

  23. Breads and Bakery Products • Flour, eggs and sugar are the sources of spoilage • Most contaminants are killed during baking but some spores can survive • Cream fillings and toppings are also excellent for bacterial growth • Most bakery products should be refrigerated during warm weather

  24. Grains • 1. The mold Aspergillus flavus produces aflatoxins in grains • These toxins are associated with liver and colon cancer in humans • 2. The fungus Claviceps purpurea produces toxins in grains (especially rye) • These toxins may induce convulsions and hallucinations • The drug LSD is derived from the toxin

  25. Food Preservation • Centuries ago humans learned that they could preserve food • Drying, salting, smoking and fermenting • In the mid 1700’s Lazarro Spallanzani showed that if beef broth was heated it would remain unspoiled • Several generations later Pasteur proved that MO’s contribute to spoilage • The purpose remains the same – to reduce the MO population and maintain it at a low level until food can be eaten

  26. Heat • Kills MO’s by denaturing their proteins • Useful in the process of canning: • Machines wash and sort the food • Subject food to steam heat for 3-5 minutes (blanching) • Food is peeled and cored and placed in cans • Containers steam sterilized (autoclave) • Process designed to eliminate the most resistant bacterial spores (Bacillus and Clostridium)

  27. If canning is not done properly, facultative or anaerobic bacteria can grow • They produce gas and cause the ends of the cans to bulge

  28. Low Temperatures • Reduce the growth rate and reproduction of MO’s • Organisms are not killed, but their numbers are kept low and spoilage is limited • Modern refrigerator operates at about 5 C • preserve food without destroying its appearance and taste • But, psychrotrophic MO’s survive (rotten eggs, sour milk)

  29. Low Temperatures • Freezer keeps food at – 5 C and ice crystals form that kill a large amount of MO’s • But, some MO’s survive and when food thaws, bacteria multiply quickly • Staphylococci • Streptococci • Rapid thawing and cooking is best • Food should not be refrozen because the bacteria deposit toxins and could cause food poisoning

  30. TEMPERATURE

  31. Drying Food • Dried foods have no water and can not support microbial life • Used to use the sun to dry foods – now there are machines • Spore-forming and capsule-producing bacteria resist drying and can survive to spoil the product once reconstituted

  32. Osmotic Pressure • Highly salted or sugared foods, the food dehydrates as well as the MO’s • Mo’s dehydrate, shrink and die • Salted foods • Ham, cod, bacon, beef, sauerkraut • Sugared foods • Jams, jellies, fruits, maple syrup

  33. Chemical Preservatives • Must inhibit growth of MO’s and also be easily broken down and eliminated from the body • Smoking foods both dehydrates them and adds chemicals that are the by-products of smoke • Major group of chemical preservatives are the organic acids • Sorbic acid, Benzoic acid, Propionic acid

  34. Chemical Preservatives • Some foods have their own natural preservatives • There are antimicrobial substances in: • Garlic – allisin is substance that is antimicrobial • Lysozyme in egg whites • Benzoic acid in cranberries

  35. Radiation • Gamma rays – high frequency forms of electromagnetic energy emitted by the radioactive isotope – cobalt 60 • The radiations are not radioactive and can’t cause food to become radioactive • They kill MO’s by reacting with and destroying microbial DNA • Can cause the breakdown of chemical bonds and formation of new ones • Maybe form new and toxic chemicals??

  36. Foodborne Disease • Food infection – Person affected by an actual MO • Bacterial – typhoid fever, salmonellosis, cholera • Protozoal – amebiasis, balantidiasis, giardiasis • Viral – hepatitis A • Food poisoning or intoxication – Person affected by the toxin an MO produces • Botulism, staphylococcal food poisoning, clostridial food poisoning

  37. Preventing Foodborne Disease • In the U.S. 2-10 million people are affected by foodborne illness annually • Can avoid them by taking basic precautions • Refrigerate perishable foods • Cover skin boils while working with food • Wash hands thoroughly • Thaw meat in refrigerator • Clean cutting boards thoroughly • Home canning should be done carefully

  38. WASH CUTTING BOARD CAREFULLY

  39. WASH HANDS

  40. Preventing Foodborne Disease • Leftovers are implicated the most so refrigerate them promptly and only keep for a few days • Picnics/barbecues: • Don’t take dairy foods (cream pies, salads) • One dish to the grill – a different one from the grill

  41. FOODS FROM MO’S • Milk products: • Lactose is the major carbohydrate in milk • Bacteria ferment lactose to lactic acid and this gives foods a sour taste (yogurt and cheese)

  42. FOODS FROM MO’S • Fermented foods: • 1. less vulnerable to extensive spoilage • 2. less likely to be vectors of foodborne illness • 3. sour taste has been accepted and sometimes considered a delicacy • Sauerkraut – Leuconostoc and Lactobacillus • Pickles – Enterobacter, Leuconostoc and Lactobacillus • Vinegar – Acetobacter aceti

  43. FOODS FROM MO’S • Other Foods: • Soy sauce • Fermented sausage • Coffee • Cocoa

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