2. Food Microbiology

3. Food Microorganisms  Bacteria  Yeast  Mold  Viruses

4. Bad and Good of Microorganisms Harmful effects: Food borne disease Food infections Food poisoning Viral borne infections Food spoilage Beneficial effects: Fermentation Cheese Yogurt Fermented sausages Wine Beer Pickles Sour kraut Probiotics Pathogens

5. Food Microbiology  spoilage: bad food microbiology –undesirable changes to food; sour milk, moldy bread –preservatives and refrigeration inhibit the growth of microorganisms

6. Food Spoilage: undesirable changes in food smell bad, taste bad, look bad probably are not harmful microorganisms that cause food spoilage compete with pathogens in the case of food spoilage vs. pathogens, the spoilers are winning

7. Food Spoilage Microorganisms bacteriayeastsmolds It is important to be able to distinguish food poisoning from food spoilage Food poisoning is when food is eaten which looks normal, smells normal and tastes normal: you eat enough to make you ill from the ingested pathogens or toxins Spoiled food does not normally cause food poisoning because it is rejected by the consumer before ingestion

8. Spoilage Microbes in Foods Bacteria The Lactic Acid Bacteria (Lactobacillus spp., Pediococcus spp., Leuconostoc spp., etc.) Pseudomonas spp. Many others Fungi Molds and Yeast

10. Food Microbiology  fermentation: good food microbiology –food that have been intentionally altered such as sour cream, cheese, beer –any desirable change a microorganism makes to food

11. Food-Borne Diseases People get sick with a food-borne disease when they consume foods or beverages contaminated with disease-causing microbes, chemicals, insects or other harmful substances

12. Probiotik Pangan/suplemen pangan yang berisi mikroba hidup yang memberi efek menguntungkan (kesehatan) saluran pencernaan

13. Spoilage Microbes--How Did They Get There? Contamination pre-harvest Contamination during processing Fungi and bacteria are everywhere!

14. Microorganism transfer Soil and Water Plants and animals Raw to processed food / cross contamination Person to Food Person to Person

15. Microorganisms in Food Food spoilage results from growth of microbes in food involves predictable succession of microbes different foods undergo different types of spoilage processes toxins are sometimes produced

16. Conditions for Spoilage Water pH Physical structure Oxygen temperature

17. Microorganism Growth in Foods

18. Microorganisms live in mixed communities Many interactions are cooperative Waste of one organism represents a nutrient for another Some cells compete for nutrients Synthesize toxic substance to inhibit growth of competitors

19. Growth of Microbes Increase in number of cells, not cell size One cell becomes colony of millions of cells microorganisms reproduce by budding or binary fission

20. Growth Increase in cellular constituents that may result in: increase in cell number( definition) when microorganisms reproduce by budding or binary fission increase in cell size coenocytic microorganisms have nuclear divisions that are not accompanied by cell divisions. Fungi have a syncytium and their nuclei are not separated. Microbiologists usually study population growth rather than growth of individual cells

21. Microbial Growth is affected by two major factors: Environmental: temperature, pH, Osmotic conditions Chemical: Proper concentrations of C, H, O, N, P, S, some trace elements, and some organic cofactors

23. Why study such a growth curve? Helps us understand how microbes grow under different conditions Helps us study the effect of different chemicals, osmotic conditions, even the effect of temperature on bacterial growth. Ex. What would the growth curve for E.coli look like if we incubated at 4 degrees Celsius? At 65?

24. Generation Time The interval required for the formation of two cells from one The process of cell division in bacteria is binary fission This is sometimes referred to as the doubling time

25. The Growth Curve Observed when microorganisms are cultivated in batch culture culture incubated in a closed vessel with a single batch of medium Usually plotted as logarithm of cell number versus time Usually has four distinct phases

26. Figure 6.1 no increase maximal rate of division and population growth population growth ceases decline in population size

27. Lag Phase Cell synthesizing new components to adapt to new medium or other conditions varies in length in some cases can be very short or even absent

28. Exponential Phase Also called log phase Rate of growth is constant Population is most uniform in terms of chemical and physical properties during this phase

29. cells are dividing and doubling in number at regular intervals

30. Balanced growth during log phase, cells exhibit balanced growth cellular constituents manufactured at constant rates relative to each other

31. Unbalanced growth rates of synthesis of cell components vary relative to each other occurs under a variety of conditions change in nutrient levels shift-up (poor medium to rich medium) shift-down (rich medium to poor medium) change in environmental conditions

32. Stationary Phase total number of viable cells remains constant may occur because metabolically active cells stop reproducing may occur because reproductive rate is balanced by death rate

33. Possible reasons for entry into stationary phase nutrient limitation limited oxygen availability toxic waste accumulation critical population density reached

34. Starvation responses morphological changes e.g., endospore formation decrease in size, protoplast shrinkage production of starvation proteins long-term survival increased virulence

35. Death Phase cells dying, usually at exponential rate death irreversible loss of ability to reproduce in some cases, death rate slows due to accumulation of resistant cells

36. Microbial growth The bacterial cell is a synthetic machine that is able to duplicate itself. The synthetic processes of bacterial cell growth involve as many as 2000 chemical reactions of a wide variety of types. Some of these reactions involve energy transformations. Other reactions involve biosynthesis of small molecules-the building, blocks of macromolecules-as well as the various cofactors and coenzymes needed for enzymatic reactions.

37. Time Lag Phase Growth Phase Stationary Phase Death Phase Bacterial Growth Curve Number of Bacteria (log 10 )

39. Time Changing the Bacterial Growth Curve *Sub-optimal means lowered: pH, A W,Temp., etc. SUB-OPTIMAL* IDEAL CONDITIONS Much longer Lag Phase Number of Bacteria (log 10 )

40. Microorganisms in Food  factors that affect the presence of microorganisms in food include –intrinsic –extrinsic

41. Intrinsic Factors 1.composition 2.physical structure 3.pH 4.presence and availability of water 5.presence of antimicrobial substances

42. 1. temperature of storage 2. relative humidity of environment 3. presence and concentration of gases 4. presence and activities of other microorganisms Exntrinsic Factors

43. Factors Affecting Microbial Growth in Foods What are the factors affecting microbial growth in foods? F-A-T-T-O-M-(P)-

45. Chemical Requirements  #1 = water!  Elements –C (50% of cell’s dry weight) HONPS –Trace elements  Organic –Source of energy (glucose) –Vitamins (coenzymes) –Some amino acids, purines and pyrimidines

46. 45 WATER  Used to dissolve materials to be transported across the cytoplasmic membrane

47. Fig. 7.4

49. Effect of nutrients on microbial growth  Microorganisms depend on nutrients for both energy and growth.  Different microorganisms possess different enzyme systems which are specific in breakdown of certain nutrient compounds.  Microbial growth can be enhanced by enriching the growth medium with specific nutrients  Creating specific nutrient media is a very useful tool both in laboratory work and in industry for isolation and growth of certain microorganisms.

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

53. pH  most acidophiles and alkalophiles maintain an internal pH near neutrality –some use proton/ion exchange mechanisms to do so  some have Acid Tolerance Response (synthesize proteins that provide protection) –e.g., acid-shock proteins

54. pH Most bacteria grow best between pH 6.5 and 7.5: Neutrophils Some bacteria are very tolerant of acidity or thrive in it: Acidophiles (preferred pH range 1 to 5) Molds and yeasts grow best between pH 5 and 6

55. Clarification of Acidity (pH) no matter what extracellular pH a microorganism prefers, intracellular pH is relatively near neutrality

57. pH scale:

58. Environmental Influencing Factors: pH neutrophiles optimum pH of 7 (neutral) most microorganisms grow best between pH of 5 (acidic) and pH of 8 (alkaline) acidophiles optimal growth, pH of less than 5.5 alkalophiles optimum pH of 8.5 or greater Copper Copper tolerant acidophile Urinary bacterial infection caused by alkaline urine

59. Acidophiles are important to mining practices The acidophiles have modifications of their membrane that allow them ot adjust their cytoplasmic pH with proton pumps

60. Temperature temperature growth range minimum to maximum temperatures for bacterial growth optimal growth temperature temperature at which the highest rate of reproduction occurs

61. Temperature Optimal Optimum growth temperature is usually near the top of the growth range Death above the maximum temp. comes from enzyme inactivation Mesophiles most common group of organisms 40ºF (5°C) slows or stops growth of most microbes

62. Classification of Bacteria by Temperature Requirements

63. Enzymes exhibit a Q 10 so that within a suitable temperature range the rate of enzyme activity doubles for every 10' C rise in temperature.

64. Temperature Considerations food preservation refrigeration inhibits fast growing mesophiles psychrophiles can still grow in refrigeration, but at a diminished rate freezing destroys microorganisms that require water to grow

65. Fig. 19-4, p. 669 40°F - 140°F = 4°C - 60°C

66. Bacteria and Temperature Bacteria die if heated for a sufficient time. The longer the time, the greater the destruction Bacteria stop growing, but do not die 4 Bacteria grow quickly 100 63 40 38 36 15 7 0 Pathogenic bacteria grow best at human body temperature 37ºC. However the majority will grow between 15-45ºC Non-sporing cells of bacteria are killed at temperatures above 60ºC. The length of time ranges depending on the organism Boiling kills living cells, but will not kill all bacterial spores Fridges should be set below 5ºC. Some bacteria such as Listeria monocytogenes can grow at refrigeration temperatures Bacteria Grow at slower rate Bacteria grow

67. Environmental Influencing Factors: temperature 5 divisions of prokaryotes, based on optimal growth temperature psychrophiles psychrotrophs mesophiles thermophiles hyperthemophiles Psychrophile: Desulfofaba gelida Thermophile: Pyrococcus sp. Hyperthermophile: Thermococcus barophilus

68. psychrophiles optimum growth temperature: - 5 0 C – 15 0 C found in the Arctic and Antarctic regions of the world Bacteria found in melt from a Russian outpost on Lake Vostok Desulfofrigus oceanense

69. Environmental Influencing Factors: temperature psychotrophs optimum growth temperature: 20 0 C – 30 0 C will grow at lower temperatures most commonly found in refrigerated food spoilage Stemphlium sarcinaeforme

70. Environmental Influencing Factors: temperature mesophiles optimum growth temperature: 25 0 C – 45 0 C most human pathogens are mesophiles –adapted well to growth in the human body, whose normal temperature is around 37 0 C Salmonella