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 Intrinsic and Extrinsic Factors

3. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 3 Intrinsic Factors composition pH presence and availability of water oxidation-reduction potential –altered by cooking physical structure presence of antimicrobial substances

4. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 4 putrefaction –proteolysis and anaerobic breakdown of proteins, yielding foul-smelling amine compounds pH impacts make up of microbial community and therefore types of chemical reactions that occur when microbes grow in food

5. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 5 Water availability measured in terms of water activity (a w ) in general, lower water activity inhibits microbial growth water activity lowered by: –drying –addition of salt or sugar osmophilic microorganisms –prefer high osmotic pressure xerophilic microorganisms prefer low a w

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7. 7 Physical structure grinding and mixing increase surface area and distribute microbes –promotes microbial growth outer skin of vegetables and fruits slows microbial growth

8. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 8 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

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

10. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 10 Microbial Growth and Food Spoilage 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

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13. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 13 Toxins ergotism –toxic condition caused by growth of a fungus in grains aflatoxins –carcinogens produced in fungus-infected grains and nut products fumonisins –carcinogens produced in fungus-infected corn algal toxins –contaminate fish and shellfish

14. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 14 Intercalate into DNA, causing frameshift mutations Aflatoxins Four basic structures - B 1, B 2, G 1, and G 2 M aflatoxins in the milk of lactating animals that have ingested type B aflatoxins

15. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 15 Disrupt synthesis and metabolism of sphingolipids Basic structure of fumonisins FB1, R = OH; FB2, R = H

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17. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 17 Controlling Food Spoilage

18. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 18 Removal of Microorganisms usually achieved by filtration commonly used for water, beer, wine, juices, soft drinks, and other liquids

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

20. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 20 High Temperature canning Pasteurization

21. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 21 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

22. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 22 Spoilage of canned goods spoilage prior to canning underprocessing leakage of contaminated water into cans during cooling process

23. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 23 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

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

25. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 25 Chemical-Based Preservation GRAS –chemical agents “generally recognized as safe” pH of food impacts effectiveness of chemical preservative

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27. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 27 Radiation ultraviolet (UV) radiation –used for surfaces of food-handling equipment –does not penetrate foods radappertization –use of ionizing radiation (gamma radiation) to extend shelf life or sterilize meat, seafoods, fruits, and vegetables –kills microbes in moist foods by producing peroxides from water peroxides oxidize cellular constituents 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

28. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 28 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 e.g., nisin –used in low-acid foods to inactivate Clostridium botulinum during canning process

29. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 29 Food-Borne Diseases two primary types –food-borne infections –food intoxications

30. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 30 Food-Borne Infection ingestion of microbes, followed by growth, tissue invasion, and/or release of toxins raw foods (e.g., sprouts, raspberries, and seafood) are important sources

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32. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 32 Food Borne Infections Salmonellosis –gastroenteritis from ingestion of contaminated meats, poultry or eggs Campylobacter jejuni –transmitted by uncooked or poorly cooked poultry products, or raw milk –gastroenteritis 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

33. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 33 Food Borne Infections… Escherichia coli –diarrhea caused by enteropathogenic, enteroinvasive and enterotoxigenic types –E. coli 0157:H7 is thought to have acquired enterohemorrhagic genes from Shigella, including genes for the shigalike toxin

34. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 34 Food Borne Infections… other organisms –viruses –protozoan pathogens –prions other concerns –foods that are transported and consumed in uncooked state sprouts shellfish and finfish raspberries

35. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 35 Cultural versus Molecular Based Virus Detection Poliovirus type 2

36. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 36 Cyclospora cayetanensis from raspberries. Bar = 5 μm. sporocysts

37. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 37 Food-Borne Intoxications ingestion of toxins in foods in which microbes have grown include staphylococcal food poisoning, botulism, Clostridium perfringens food poisoning, and Bacillus cereus food poisoning

38. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 38 Detection of Food-Borne Pathogens must be rapid and sensitive methods include: –culture techniques – may be too slow –immunological techniques - very sensitive –molecular techniques probes used to detect specific DNA or RNA sensitive and specific

39. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 39 Autoradiogram of a radioactively-labeled Listeria monocytogenes DNA probe against 100 Listeria spp. cultures. Molecular Probes and Food Microbiology

40. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 40 Comparison of PCR and growth for detection of Salmonella PCR-based Pathogen Detedtion

41. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 41 Surveillance for food-borne disease… PulseNet –established by Centers for Disease Control and Prevention, USA –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

42. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 42 Surveillance… FoodNet –active surveillance network used to follow nine major food-borne diseases –enables public health officials to rapidly trace the course and cause of infection in days rather than weeks

43. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 43 Microbiology of Fermented Foods major fermentations - lactic, propionic, and ethanolic fermentations

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45. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 45 Fermented Milks majority of fermented milk products rely on lactic acid bacteria belonging to the genera Lactobacillus, Lactococcus, Leuconostoc, and Streptococcus –gram-positives that tolerate acidic conditions, are non-spore forming, and are aerotolerant with a strictly fermentative metabolism

46. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 46 Lactobacillus helveticus Lactobacillus delbrueckii sub. bulgaricus Lactobacillus lactis

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

48. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 48 A light microscope of Bifidobacterium sp.

49. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 49 Examples of Bifid-amended dairy products.

50. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 50 Fermented Milks… Yeast-lactic fermentation –yeasts, lactic acid bacteria, and acetic acid bacteria –kefir Mold-lactic fermentation –filamentous fungi and lactic acid bacteria –viili

51. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 51 Cheese Production milk lactic acid bacteria and rennin  curd removal of whey  ripening by microbial action  cheese

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53. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 53 Gouda cheese cheddar cheese Roquefort cheese Swiss cheese Brie cheese (soft/ripened) Limburger cheese (soft/ripened) Cottage cheese (soft/unripened) cream cheese (soft/unripened)

54. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 54 Cheddar cheese production

55. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 55 Fermented Meat and Fish sausages hams bologna salami izushi – fish, rice, and vegetables (Lactobacillus spp.) katsuobushi – tuna (Aspergillus glaucus)

56. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 56 Production of Alcoholic Beverages begins with formation of liquid containing carbohydrates in readily fermentable form –must juice from crushed grapes –mashing hydrolysis of complex carbohydrates in cereals by addition of water and incubation yields wort – clear liquid containing fermentable carbohydrates

57. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 57 racking – removes sediments or Microbial oxidation of ethanol to acetic acid yields wine vinegar

58. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 58 Beers and ales 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

59. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 59 Beers and ales… wort is then 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

60. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 60 (pitched) Beer Production

61. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 61 Distilled spirits similar to beer-making process - following fermentation, is distilled to concentrate alcohol Scotch whiskey –begins with sour mash mash inoculated with homolactic bacterium

62. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 62 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

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

65. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 65 Making sauerkraut

66. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 66 Microorganisms as Foods and Food Amendments variety of bacteria, yeasts, and other fungi (mushrooms) are used as animal and human food sources probiotics –microbial dietary adjuvants : e.g. Spirulina, lactic acid bacteria, etc. –microbes added to diet in order to provide health benefits beyond basic nutritive value

67. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 67 Benefits of probiotics immunodilation control of diarrhea anticancer effects possible modulation of Crohn’s disease in beef cattle, –decrease E. coli (O157:H7) in poultry, –limit colonization of gut by the process of competitive exclusion

68. Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 68 Prebiotics oligosaccharide polymers that are not processed until they enter large intestine synbiotic system –combination of prebiotics and probiotics –results in production of certain acids that may be responsible for possible beneficial effects of probiotics