1. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 1 Chapter 40 Microbiology of Food

2. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 2 Microbial Growth and Food Spoilage results from growth of microbes in food –alters food visibly and in other ways, rendering it unsuitable for consumption involves predictable succession of microbes different foods undergo different types of spoilage processes toxins are sometimes produced

3. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 3 Microbial Growth and Food Spoilage… microbial growth is controlled by –intrinsic factors factors related to the food itself –extrinsic factors environment where food stored

4. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 4 Figure 40.1

5. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 5 Intrinsic Factors food composition - carbohydrates –mold predominates degrades food by hydrolysis, tomatoes particularly susceptible little odor ergotism –hallucinogenic alkaloids released by Claviceps purpurea –may cause death

6. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 6 Table 40.1

7. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 7 Figure 40.2

8. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 8 Intrinsic Factors… food composition – proteins or fats –bacterial growth predominates putrefaction –proteolysis and anaerobic breakdown of proteins, yielding foul-smelling amine compounds unpasteurized milk spoilage –acid production followed by putrification butter –short chained fatty acid production results in rancid butter

9. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 9 Figure 40.3

10. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 10 Figure 40.4

11. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 11 Intrinsic Factors… pH –impacts make up of microbial community and therefore types of chemical reactions that occur when microbes grow in food –e.g., low pH favors yeast and mold presence and availability of water –in general, lower water activity inhibits microbial growth

12. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 12 Intrinsic Factors… oxidation-reduction potential –altered by cooking –lower redox – more bacteria and anaerobes physical structure –grinding and mixing distribute microbes; promotes microbial growth –outer skin of vegetables and fruits slows microbial growth

13. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 13 Antimicrobial Substances coumarins – fruits and vegetables lysozyme – cow’s milk and eggs aldehydic and phenolic compounds – herbs and spices allicin – garlic polyphenols – green and black teas

14. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 14 Extrinsic Factors temperature –lower temperatures retard microbial growth relative humidity –higher levels promote microbial growth atmosphere –oxygen promotes growth –modified atmosphere packaging (MAP) use of shrink wrap and vacuum technologies to package food in controlled atmospheres

15. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 15 Controlling Food Spoilage modern era of food microbiology established by Louis Pasteur in 1857 methods of preservation –goal is to eliminate or reduce the populations of spoilage and disease causing microbes while maintaining food quality

16. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 16 Removal of Microorganisms water, wine, beer, juices, soft drinks, and other liquids usually by filtration may better preserve flavor and aroma

17. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 17 Low Temperature refrigeration at 5°C retards but does not stop microbial growth –microorganisms can still cause spoilage with extended spoilage –growth at temperatures below -10°C has been observed

18. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 18 High Temperature: Canning food heated in special containers (retorts) to 115°C for 25 to 100 minutes kills spoilage microbes, but not necessarily all microbes in food spoilage of canned foods –spoilage prior to canning –underprocessing –leakage of contaminated water into cans during cooling process

19. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 19 Figure 40.5

20. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 20 Pasteurization kills pathogens and substantially reduces number of spoilage organisms different pasteurization procedures heat for different lengths of time –shorter heating times result in improved flavor

21. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 21 Water Availability dehydration –e.g., lyophilization to produce freeze- dried foods is commonly used to eliminate bacterial growth –food preservation occurs as a result of free-water loss and an increase in solute concentration

22. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 22 Table 40.2

23. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 23 Chemical-Based Preservation GRAS –chemical agents “generally recognized as safe” –agents include organic acids, sulfite, ethylene oxide gas, ethyl formate –sodium nitrite – inhibits spore formation in meats, forms nitrosamines pH of food impacts effectiveness of chemical preservative

24. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 24 Table 40.3

25. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 25 Radiation radappertization –use of ionizing radiation (gamma radiation) to extend shelf life or sterilize meat, seafoods, fruits, and vegetables –excellent penetrating power – food not radioactive –kills microbes in moist foods by producing peroxides from water peroxides oxidize cellular constituents

26. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 26 Radiation… electron beams –electrons are electrically generated, so can be turned on only when needed –does not generate radioactive waste, but also does not penetrate foods as deeply as gamma radiation

27. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 27 Microbial Product-Based Inhibition bacteriocins –bactericidal proteins active against related species –some dissipate proton motive force of susceptible bacteria –some form pores in plasma membranes –some inhibit protein or RNA synthesis

28. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 28 Microbial Product-Based Inhibition e.g., nisin from Lactococcus lactis –used in low-acid foods to inactivate Clostridium botulinum during canning process e.g., bacteriophages that kill Listeria monocytogenes –sprayed onto ready-to-eat meats prior to packaging

29. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 29 Packaging modified atmosphere packaging (MAP) –gases in stored food affect microbial growth –shrink wrap materials and vacuum technology control atmosphere impermeable to oxygen superoxide radicals inhibit growth –polylactic acid green alternative to plastic made from wood and corn embedded with nisin which is slowly released

30. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 30 Types of Food-Borne Disease about 76 million cases/yr in U.S. –18% attributed to known pathogens –at least 5,000 deaths/yr in U.S. pathogens –Noroviruses, Campylobacter jejuni, Salmonella are major causes –E. coli and Listeria are also important pathogens

31. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 31 Types of Food-Borne Disease… two primary types –food-borne infections –food intoxications transmission –breakdown in hygiene –fecal-oral route key –fomites also important

32. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 32 Food-Borne Infection ingestion of pathogen, followed by growth, tissue invasion, and/or release of toxins raw foods (e.g., sprouts, raspberries, and seafood) are important sources

33. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 33 Table 40.4

34. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 34 Food-Borne Infections… Listeriosis –pregnant women, the young and old, and immunocompromised individuals most vulnerable –responsible for the largest meat recall in U.S. –at-risk people should not eat soft cheeses, refrigerated smoked meats, deli meats, and undercooked hot dogs

35. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 35 Food-Borne Intoxications ingestion of toxins in foods in which microbes have grown produce symptoms shortly after the food is consumed because growth of the disease-causing microorganism is not required include staphylococcal food poisoning, botulism, Clostridium perfringens food poisoning, and Bacillus cereus food poisoning

36. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 36 Other Food Disease enterohemorrhagic E. coli (O157:H7) –normal inhabitant of intestines of mammals including cattle, swine contamination of meat during slaughter in salad vegetables contaminated in field –shiga toxin from horizontal gene transfer from Shigella may result in life-threatening hemolytic uremic syndrome, most common in children and elderly

37. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 37 Other Food Disease fungus-derived toxins –aflatoxins carcinogens produced in fungus-infected grains and nut products –fumonisins carcinogens produced in fungus-infected corn algal toxins contaminate fish and shellfish

38. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 38 Figure 40.6

39. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 39 Figure 40.7

40. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 40 Detection of Food-Borne Pathogens must be rapid, sensitive and simple and for prevention methods include: –culture techniques – may be too slow but are most likely to detect food pathogens –immunological techniques - very sensitive –molecular techniques probes used to detect specific DNA or RNA sensitive and specific

41. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 41 Detection of Food-Borne Pathogens… PulseNet –established by Centers for Disease Control –uses pulsed-field gel electrophoresis under carefully controlled and duplicated conditions to determine distinctive DNA pattern of each bacterial pathogen –enables public health officials to link pathogens associated with disease outbreaks in different parts of the world to a specific food source

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43. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 43 Detection of Food-Borne Pathogens… in addition to PFGE, PCR and RFLP are increasingly developed and used –amplify small quantities –species specific –microarray techniques directly from food or water

44. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 44 Figure 40.9

45. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 45 Microbiology of Fermented Foods chemical changes in food brought about microbial action major fermentations used are lactic, propionic, and ethanolic fermentations

46. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 46 Fermented Milks majority of fermented milk products rely on lactic acid bacteria (LAB) belonging to the genera Lactobacillus, Lactococcus, Leuconostoc, and Streptococcus –gram-positives that tolerate acidic conditions, non-spore forming, aerotolerant with a strictly fermentative metabolism

47. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 47 Figure 40.10

48. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 48 Table 40.5

49. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 49 Fermented Milks… mesophilic –Lactobacillus and Lactococcus –buttermilk and sour cream thermophilic –Lactobacillus and Streptococcus –yogurt probiotics –Lactobacillus and Bifidobacterium –addition of microbes to the diet to improve health beyond basic nutritive value

50. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 50 Probiotics and Standardization probiotics –live microorganisms, which when administered in adequate amounts, confer a health benefit to the host –specific requirements should be met microorganisms –Lactobacillus, Bifidobacterium

51. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 51 Figure 40.11

52. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 52 Benefits of Probiotics immunomodulation control of diarrhea anticancer effects – colon cancer possible modulation of Crohn’s Disease treatment of enteric disease –competition with pathogens –antibiotic resistance is continually rising

53. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 53 Benefits of Probiotics… Lactobacillus acidophilus and Bifidobacterium –improve lactose intolerance –improves general intestinal health and balance –may lower serum cholesterol –may have anti-tumor activity

54. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 54 Other Milk Fermentations yeast lactic –yeasts, lactic acid bacteria, and acetic acid bacteria –kefir mold lactic –filamentous fungi and lactic acid bacteria –villi

55. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 55 Cheese Production approximately 2,000 distinct varieties representing 20 general types classified based on –texture, hardness (soft, semi-soft, hard, very hard) all from lactic acid fermentation –molds may further enhance

56. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 56 Cheese Production… milk lactic acid bacteria and rennin  curd removal of whey  ripening by microbial action  cheese

57. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 57 Table 40.6

58. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 58 Figure 40.12

59. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 59 Meat and Fish sausages hams bologna salami izushi – fish, rice, and vegetables katsuobushi – tuna

60. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 60 Wines and Champagnes enology (wine production) –crushed grapes separation and storage of liquid (must) before fermentation –fresh must treated with sulfur dioxide fumigant Saccharomyces cerevisiae or S. liposideus added for consistent results fermented for 3–5 days at 20–28 o C

61. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 61 Figure 40.13

62. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 62 Wines and Champagnes… dry or sweet wines –controlled by regulating initial must sugar content racking –removes sediment produced during fermentation

63. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 63 Beers and Ales cereal grains used for fermentation –malt germinated barley grains having activated enzymes –mash the malt after being mixed with water in order to hydrolyze starch to usable carbohydrates –mash heated with hops hops provide flavor and assist in clarification of wort heating inactivates hydrolytic enzymes

64. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 64 Figure 40.14

65. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 65 Beers and Ales… wort inoculated (pitched) with desired yeast –bottom yeasts used in production of beers –top yeasts used in production of ales freshly fermented beers are aged or lagered –CO 2 usually added at bottling beer can be pasteurized or sterilized by filtration

66. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 66 Figure 40.15

67. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 67 Distilled Spirits similar to beer-making process –begins with sour mash mash inoculated with homolactic bacterium –following fermentation, is distilled to concentrate alcohol

68. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 68 Production of Breads involves growth of Saccharomyces cerevisiae (baker’s yeast) under aerobic conditions –maximizes CO 2 production, which leavens bread other microbes used to make special breads (e.g., sourdough bread) can be spoiled by Bacillus species that produce ropiness

69. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 69 Other Fermented Foods… sufu – from fermentation of tofu sauerkraut (sour cabbage) – from wilted, shredded cabbage pickles – from cucumbers silage – from grass, chopped corn, and other fresh animal feeds

70. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 70 Table 40.7

71. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 71 Microorganisms as Foods and Food Amendments mushrooms (e.g., Agaricus bisporus) cyanobacterium Spirulina dried cakes probiotics –Lactobacillus acidophilus in beef cattle decrease E. coli O157:H7 –Bacillus subtilis (PREEMPT) in poultry limit colonization of gut by the process of competitive exclusion reduces Salmonella and Campylobacter

72. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 72 Figure 40.16