Chapter 3 Sterilization

1. Chapter 3 Sterilization Unit 1 Medium Sterilization Unit 2 Air Sterilization

2. Basic terms • Sterilization • Disinfection • Antisepsis • Bacteriostasis • Asepsis

3. Sterilization Destruction of all forms of microbial life, including bacterial spores. More thorough than disinfection

4. Disinfection • To kill most of microbial forms except • some resistant organisms or bacterium • spores. • e.g. use of alcohol before drug injection.

5. About sterilization and disinfection, which is wrong? A.Sterilization is the killing of all microorganisms in a material or on the surface of an object. B.Disinfection means reducing the number of viable microorganisms present in a sample. C.Typically the last things to die when one attempts sterilization is the highly heat- (and chemical-, etc.) resistant endospores. D.All disinfectants are capable of sterilizing.

6. Antisepsis Process of inhibiting or preventing growth of microbes, mostly in vitro and not bactericidal or sporicidal. e.g. use of chemical agents on skin, other living tissues or food/beverage.

7. Bacteriostasis Process of inhibiting the growth of microorganisms, in vivo (mostly) or in vitro. e.g. bacteriostatic antibiotics

8. Total cell count Viable cell count Log Cell # Time Different Kinds of Bacteria “Death” 1. Bacteriostatic 2. Bacteriocidal 3. Bacteriolytic

9. Asepsis • No living microorganisms exists. e.g. OR (Operating Room)

11. Sterilization conveniently categorized as follows • I. Physical methods • ① Heat : • Dry heat • Moist heat • ② Radiations • Ultraviolet radiations • Ionizing radiations • ③ Filtration • II. Chemical methods

12. Alcohols,Chlorine, Formalin Suitable for skin and instruments 1.Chemical agents Ultraviolet and Ionizing Radiation Suitablefor sterile room and inoculation hood 2. Radiation Direct flaming: e.g. inoculating loop Hot-air sterilization :160 ℃, 2h in hot air oven 3. Dry Heat 121℃，30min in autoclave Suitable for medium and instruments 4. Moist Heat Removal of bacteria by filter medium Used for heat sensitive materials and filtrated air 5. Filtration

13. Heat sterilization –how it works? • Dry heat- protein oxidation • Moist heat- proteindenaturation

14. Dry Heat • Flaming • Hot air oven • -170 °C for 1 hour • -140 °C for 3 hours • .

15. Moist Heat • 1. Pasteurization( below 100 °C) • Destroys pathogens without altering the • flavor of the food. • Low temperature (holding method): 63 ℃ , 30 min • High temperature (flash method): 72 ℃ , 20sec

16. 2. Boiling (at 100 °C) -killing most vegetative forms of bacteria -10 min or longer time 3. Autoclaving (above 100 °C) -killing both vegetative organisms and endospores -121-132 oC for 15 min or longer

17. Moist Heat vs Dry Heat Moist heat Dry heat Penetrating potency higher lower Temp. for protein clotting lower higher Extra heat released yes no from condensation Sterilizing potency: Moist heat ﹥﹥Dry heat

18. Why is moist heat more efficient than dry heat ? Conductivity. Moisture conducts the heat better than a dry system.

19. dry heat or moist heat? • is less penetrating and requires longer exposure. • An autoclave is a high pressure device used to allow the application of above the normal-atmosphere boiling point of water. • Pasteurization is the application ofof less-than boiling temperatures to foods to prevent the growth of food-spoiling organisms as well as various heat-labile pathogens.

20. Canned food could be stored for a long time, because A. Bacteria can’t go into can. B. Bacteria can’t breath in can. C. There are no bacteria in can. D. Bacteria can’t survival in can.

21. Sterilization processes • Batch sterilization • Continuous sterilization

22. Batch sterilization Batch sterilization uses steam or direct firing to elevate the temperature, and then cooling water stops the process and brings the material back toward room temperature.

24. Batch sterilization wastes energy and can overcook the medium Continuous sterilization is used to almost eliminate these undesired times because there can be more rapid heat transfer to flowing medium in pipes.

25. Continuous sterilization • Also called high temperature short time (HTST) • Generally carried out at 140°C, whereby sterilization times of 2-3 min are sufficient

26. What are the equipments of continuous sterilization? Question stream Cooling water fermentor Sterile medium stream mixing tank pump sterilizing column Maintaining tank cooling pipe

27. Injection sterilizers Steam is fed directly into raw medium, so that temp. rises to desired level almost immediately. Continuous sterilization processes

28. Advantages • Shorter sterilization time means less thermal degradation of medium.

29. Disadvantages • Insufficient for sterilizing media containing solid matter, on account of inferior rate of heat-transfer in solids. (batch process is recommended for sterilizing such media.)

30. Batch and Continuous Sterilization

31. In a word: High temperatures for short times are used in preparing nutrient media for industrial fermentations and in pasteurizing milk, because this causes less damage to biochemicals than more prolonged times at lower temperatures.

32. Filtration Sterilize solutions that may be damaged or denatured by high temperatures or chemical agents.

33. The pore size for filtering bacteria, yeasts, and fungi is in the range of 0.22-0.45 μm(filtration membranes are most popular for this purpose).

36. Filtration: Fluids & Air

37. Unit 2 Air Sterilization • Very large volumes of sterile air is required in many aerobic fermentation process.

38. Methods for air sterilization • Radiation • High temperature • Electrostatic bacteria removal • Filtration

39. Air sterilization is generally carried out by filtration to remove all particles and m/o (bacteria, spores, yeast, mould) from atmospheric flow. • For reason of cost, absolute sterility is neither possible nor customary in practice.

40. For germ-filtration of liquids (hydrophobic membrane filters), the pore width is 0.2 μm. • For air-filtration, the pore width of filters is over 0.45 m .

41. Removal of m/o from air by the fibrous • filter may occur by one, or combination of • the following mechanisms: • Inertial impaction • Interception • Diffusion • Electrostatic attraction

42. Removal mechanisms –Size exclusion

43. – Diffusional Interception – Electrostatic Attraction – Inertial impaction

44. Depth Filters • Fibrous material (cellulose, synthetic fibers, glass fibers) • Granular material(activated charcoal )

45. Air outlet Support grid Stainless steel casing Fibrous filter packing Support grid Air inlet Simple air filter

47. Contaminants in Compressed Air • Atmospheric dust, smoke, fumes, water vapour, bacteria and viruses! • Oil carried over from the compressor. • Solid contaminants generated within the system.

48. The propose of air pretreatment • Making air more clean • -upper air collecting pipe • -coarse filter • Oil and water discharge

49. example The process of air filtration 1.Coarse filter 5. Cyclone separator 2. Air compressor(120150℃) 7. Wire mesh demister 3. Recover tank 8. Heater(3035℃) 4.6. Cooler (2025℃) 9. Filter

50. Cyclone separator