Lecture 18 Food Microbiology.ppt


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Lecture 18 Food Microbiology.ppt

  1. 1. Lecture #9 Food Microbiology
  2. 2. Conditions for Spoilage <ul><li>Water </li></ul><ul><li>pH </li></ul><ul><li>Physical structure </li></ul><ul><li>Oxygen </li></ul><ul><li>temperature </li></ul>
  3. 3. Microorganism Growth in Foods
  4. 4. Intrinsic Factors <ul><li>composition </li></ul><ul><li>pH </li></ul><ul><li>presence and availability of water </li></ul><ul><li>oxidation-reduction potential </li></ul><ul><ul><li>altered by cooking </li></ul></ul><ul><li>physical structure </li></ul><ul><li>presence of antimicrobial substances </li></ul>
  5. 5. Composition and pH <ul><li>putrefaction </li></ul><ul><ul><li>proteolysis and anaerobic breakdown of proteins, yielding foul-smelling amine compounds </li></ul></ul><ul><li>pH impacts make up of microbial community and therefore types of chemical reactions that occur when microbes grow in food </li></ul>
  6. 6. Water availability <ul><li>in general, lower water activity inhibits microbial growth </li></ul><ul><li>water activity lowered by: </li></ul><ul><ul><li>drying </li></ul></ul><ul><ul><li>addition of salt or sugar </li></ul></ul><ul><li>osmophilic microorganisms </li></ul><ul><ul><li>prefer high osmotic pressure </li></ul></ul><ul><li>xerophilic microorganisms </li></ul><ul><ul><li>prefer low water activity </li></ul></ul>
  7. 7. Physical structure <ul><li>grinding and mixing increase surface area and distribute microbes </li></ul><ul><ul><li>promotes microbial growth </li></ul></ul><ul><li>outer skin of vegetables and fruits slows microbial growth </li></ul>
  8. 8. Antimicrobial substances <ul><li>coumarins – fruits and vegetables </li></ul><ul><li>lysozyme – cow’s milk and eggs </li></ul><ul><li>aldehydic and phenolic compounds – herbs and spices </li></ul><ul><li>allicin – garlic </li></ul><ul><li>polyphenols – green and black teas </li></ul>
  9. 9. Extrinsic Factors <ul><li>temperature </li></ul><ul><ul><li>lower temperatures retard microbial growth </li></ul></ul><ul><li>relative humidity </li></ul><ul><ul><li>higher levels promote microbial growth </li></ul></ul><ul><li>atmosphere </li></ul><ul><ul><li>oxygen promotes growth </li></ul></ul><ul><ul><li>modified atmosphere packaging (MAP) </li></ul></ul><ul><ul><ul><li>use of shrink wrap and vacuum technologies to package food in controlled atmospheres </li></ul></ul></ul>
  10. 10. Microbial Growth and Food Spoilage <ul><li>food spoilage </li></ul><ul><ul><li>results from growth of microbes in food </li></ul></ul><ul><ul><ul><li>alters food visibly and in other ways, rendering it unsuitable for consumption </li></ul></ul></ul><ul><ul><li>involves predictable succession of microbes </li></ul></ul><ul><ul><li>different foods undergo different types of spoilage processes </li></ul></ul><ul><ul><li>toxins are sometimes produced </li></ul></ul><ul><ul><ul><li>algal toxins may contaminate shellfish and finfish </li></ul></ul></ul>
  11. 12. Food Spoilage <ul><li>Approximately 1/3 rd of all food manufactured in world is lost to spoilage </li></ul><ul><li>Microbial content of foods (microbial load): qualitative (which bugs) and quantitative (how many bugs) </li></ul><ul><li>Shelf life </li></ul><ul><ul><li>Non-perishable foods (pasta) </li></ul></ul><ul><ul><li>Semiperishable foods (bread) </li></ul></ul><ul><ul><li>Perishable foods (eggs) </li></ul></ul>
  12. 13. General Principles <ul><li>Minimize contamination by: </li></ul><ul><ul><li>Good management processes </li></ul></ul><ul><ul><li>Acceptable sanitary practices </li></ul></ul><ul><ul><li>Rapid movement of food through processing plant </li></ul></ul><ul><ul><li>Well-tested preservation procedures </li></ul></ul>
  13. 14. Spoilage <ul><li>Meat </li></ul><ul><ul><li>Cutting board contamination </li></ul></ul><ul><ul><li>Conveyor belts </li></ul></ul><ul><ul><li>Temperature </li></ul></ul><ul><ul><li>Failure to distribute quickly </li></ul></ul><ul><ul><li>Fecal bacteria from intestines </li></ul></ul><ul><li>Fish </li></ul><ul><ul><li>Polluted waters </li></ul></ul><ul><ul><li>Transportation boxes </li></ul></ul>
  14. 15. Spoilage <ul><li>Poultry and Eggs </li></ul><ul><ul><li>Human contact </li></ul></ul><ul><ul><li>Penetration by bacteria </li></ul></ul><ul><li>Milk and Dairy Products </li></ul><ul><ul><li>Lactobacillus and Streptococcus species that survive pasturization (sour milk) </li></ul></ul><ul><li>Breads </li></ul><ul><ul><li>Spores and fungi that survive baking </li></ul></ul><ul><li>Grains </li></ul><ul><ul><li>Fungi produce toxins </li></ul></ul>
  15. 16. Food-Borne Diseases <ul><li>two primary types </li></ul><ul><ul><li>food-borne infections </li></ul></ul><ul><ul><li>food intoxications </li></ul></ul>
  16. 17. Preventing Foodborne Disease <ul><li>Food infections (microbes are transferred to consumer) </li></ul><ul><li>Food poisoning (results from the toxin consumption) </li></ul>
  17. 19. Food-Borne Intoxications <ul><li>ingestion of toxins in foods in which microbes have grown </li></ul><ul><li>include staphylococcal food poisoning, botulism, Clostridium perfringens food poisoning, and Bacillus cereus food poisoning </li></ul>
  18. 20. Toxins <ul><li>ergotism </li></ul><ul><ul><li>toxic condition caused by growth of a fungus in grains </li></ul></ul><ul><li>aflatoxins </li></ul><ul><ul><li>carcinogens produced in fungus-infected grains and nut products </li></ul></ul><ul><li>fumonisins </li></ul><ul><ul><li>carcinogens produced in fungus-infected corn </li></ul></ul>
  19. 22. Controlling Food Spoilage
  20. 23. Removal of Microorganisms <ul><li>usually achieved by filtration </li></ul><ul><li>commonly used for water, beer, wine, juices, soft drinks, and other liquids </li></ul>
  21. 24. Low Temperature <ul><li>refrigeration at 5 °C retards but does not stop microbial growth </li></ul><ul><ul><li>psychrophiles and psychrotrophs can still cause spoilage </li></ul></ul><ul><ul><li>growth at temperatures below -10 °C has been observed </li></ul></ul>
  22. 25. High Temperature <ul><li>canning </li></ul><ul><li>pasteurization </li></ul>
  23. 26. Canning <ul><li>food heated in special containers (retorts) to 115 °C for 25 to 100 minutes </li></ul><ul><li>kills spoilage microbes, but not necessarily all microbes in food </li></ul>
  24. 27. Spoilage of canned goods <ul><li>spoilage prior to canning </li></ul><ul><li>underprocessing </li></ul><ul><li>leakage of contaminated water into cans during cooling process </li></ul>
  25. 28. Pasteurization <ul><li>kills pathogens and substantially reduces number of spoilage organisms </li></ul><ul><li>different pasteurization procedures heat for different lengths of time </li></ul><ul><ul><li>shorter heating times result in improved flavor </li></ul></ul>
  26. 29. Water Availability
  27. 30. Chemical-Based Preservation <ul><li>GRAS </li></ul><ul><ul><li>chemical agents “generally recognized as safe” </li></ul></ul><ul><li>pH of food impacts effectiveness of chemical preservative </li></ul>
  28. 32. Radiation <ul><li>ultraviolet (UV) radiation </li></ul><ul><ul><li>used for surfaces of food-handling equipment </li></ul></ul><ul><ul><li>does not penetrate foods </li></ul></ul><ul><li>Gamma radiation </li></ul><ul><ul><li>use of ionizing radiation (gamma radiation) to extend shelf life or sterilize meat, seafoods, fruits, and vegetables </li></ul></ul>
  29. 33. Detection of Food-Borne Pathogens <ul><li>must be rapid and sensitive </li></ul><ul><li>methods include: </li></ul><ul><ul><li>culture techniques – may be too slow </li></ul></ul><ul><ul><li>immunological techniques - very sensitive </li></ul></ul><ul><ul><li>molecular techniques </li></ul></ul><ul><ul><ul><li>probes used to detect specific DNA or RNA </li></ul></ul></ul><ul><ul><ul><li>sensitive and specific </li></ul></ul></ul>
  30. 34. comparison of PCR and growth for detection of Salmonella
  31. 35. nucleic acid can be detected even when plaque-forming ability is lost
  32. 36. Surveillance for food-borne disease <ul><li>PulseNet </li></ul><ul><ul><li>established by Centers for Disease Control </li></ul></ul><ul><ul><li>uses pulsed-field gel electrophoresis under carefully controlled and duplicated conditions to determine distinctive DNA pattern of each bacterial pathogen </li></ul></ul><ul><ul><li>enables public health officials to link pathogens associated with disease outbreaks in different parts of the world to a specific food source </li></ul></ul>
  33. 37. Surveillance… <ul><li>FoodNet </li></ul><ul><ul><li>active surveillance network used to follow nine major food-borne diseases </li></ul></ul><ul><ul><li>enables public health officials to rapidly trace the course and cause of infection in days rather than weeks </li></ul></ul>
  34. 38. Helpful Suggestions <ul><li>Refrigerate quickly </li></ul><ul><li>Wash hands </li></ul><ul><li>Clean cutting boards </li></ul><ul><li>Leftovers </li></ul><ul><li>Avoid home-canned foods </li></ul>
  35. 39. Microbiology of Fermented Foods <ul><li>major fermentations used are lactic, propionic, and ethanolic fermentations </li></ul>
  36. 40. Fermentation Any partial breakdown of carbohydrates taking place in the absence of oxygen.
  37. 43. Meat and Fish <ul><li>sausages </li></ul><ul><li>hams </li></ul><ul><li>bologna </li></ul><ul><li>salami </li></ul><ul><li>izushi – fish, rice and vegetables </li></ul><ul><li>katsuobushi – tuna </li></ul>
  38. 44. Wine White vs. Red: juice or juice and skin Yeasts: Ferment when no oxygen around. Saccharomyces species Dry Sweet Sparkling Fortified
  39. 45. Production of Breads <ul><li>involves growth of Saccharomyces cerevisiae (baker’s yeast) under aerobic conditions </li></ul><ul><ul><li>maximizes CO 2 production, which leavens bread </li></ul></ul><ul><li>other microbes used to make special breads (e.g., sourdough bread) </li></ul><ul><li>can be spoiled by Bacillus species that produce ropiness </li></ul>
  40. 46. Other Fermented Foods <ul><li>silages </li></ul><ul><ul><li>fermented grass, corn, and other fresh animal feeds </li></ul></ul>
  41. 47. Microorganisms as Foods and Food Amendments <ul><li>variety of bacteria, yeasts, and other fungi are used as animal and human food sources </li></ul><ul><li>probiotics </li></ul><ul><ul><li>microbial dietary adjuvants </li></ul></ul><ul><ul><li>microbes added to diet in order to provide health benefits beyond basic nutritive value </li></ul></ul>