1. Factors affecting survival and growth FS0501 12000

2. Traditional food preservation - Stored in cool caves Cheese, fruits, vegetables - Frozen / freeze-dried at Meat (Switzerland), high latitudes and altitudes potato (Peru) - Dried in the sun - Smoked / dried over fires - Salted and dried - Fermented FS0501 2 2000 Tomato (Italy), fish, meat (South America), Biltong (South Africa) Kipper (UK, smoked herring) Bacalhau (Portugal - dried cod) Tempeh, cheese, wine, beer, yoghurt, kefir

3. Pasteur’s germ theory Traditional methods work by ‹ Preventing contamination ‹ Destroying microorganisms ‹ Inhibiting growth of undesirable microorganisms FS0501 32000

4. Traditional food preservation Traditional preservation sometimes fails to preserve the food, or to kill the pathogens. In these cases, spoilage or food poisoning may occur. Examples: salmonellosis from dried beef (Salmonella St. Paul ) and poisoning from tempeh bonkrek in Indonesia. FS0501 42000

5. Traditional food preservation Certain “traditional” foods can be manufactured using industrial processes Example: Soy sauce FS0501 52000

6. Factors affecting growth of bacteria in food - Temperature - Time - pH - Water activity (a w ) - Oxygen tension - Preservatives - Microbial interactions FS0501 62000

7. Temperature Boiling point Pasteurising temperature Body temperature Fridge Freezer FS0501 7 2000 100° 72° 60° 36.5° 10° 0° SAFETY DANGER SAFETY

8. How temperature affects growth rate of a bacterial population B (Optimum) C (Minimum)A (Maximum) ColdHot Temperature FS0501 82000

9. Growth of S. typhimurium at different temperatures 9 8 725° 6 20° 5 15° 4 10° 32103210 012345 Time (Days) FS0501 92000

10. Temperature range for growth of pathogens Temperature°C Min.Opt.Max. Salmonella535 - 3747 Campylobacter304247 E. coli103748 S. aureus6.537 - 4048 C. botulinum (proteolytic)1050 C. botulinum (non-proteolytic)3.325 - 37 B. cereus430 - 3548 - 50 1 43 2 FS0501 102000

11. Temperature range for growth of toxigenic moulds Temperature °C Min. Opt. Max. Penicillium verrucosum Aspergillus ochraceus Aspergillus flavus Fusarium moniliforme FS0501 11 2000 0 20 31 8 28 37 10 32 42 3 25 37

12. Growth of different bacteria at 25°C 9 8787 6 5 Log 4 CFU 3 2 1 0 FS0501 12 2000 01 2 Time (Days) S. typhimurium L. monocytogenes Ps. fluorescens B. cereus C. bot-Proteolytic G+ve Spoilers 3 4

13. Effect of temperature on time to botulinum toxin production 10 9 8 7 6 5 4 3 2 1 0 FS0501 13 2000 0 Vacuum-packed hot smoked trout Salt concentration = 0.5% 5 10 15 Temperature (°C) 20 25

14. Temperature affects bacteria ‹ Lag phase ‹ Growth rate ‹ Final cell numbers through the change in ‹ Enzymatic and chemical composition of cells ‹ Nutritional requirements ‹ Limits for other factors influencing growth FS0501 142000

15. Effect of salt concentration on time to botulinum toxin production 16 14 12 10 8 6 4 2 0 FS0501 15 2000 0 10°C 14°C 18°C 24°C 0.5 1 Salt Concentration (%) 1.5 2

16. Limits of pH for growth of pathogens pH MinMax. Escherichia coli4.48.5 Salmonella typhi4 - 4.58 - 9.6 Bacillus cereus4.99.3 Clostridium botulinum4.68.5 Staphylococcus aureus49.8 Saccharomyces cerevisiae2.38.6 Aspergillus flavus2.011.2 Fusarium moniliforme2.510.7 Penicillium verrucosum2.010.0 FS0501 162000

17. Definition of water activity (a w ) a W = p / p o a w is the ratio of the water vapour pressure of the food (p) to that of pure water (p o ) at the same temperature. FS0501 172000

18. Effect of water activity on lag time of S. aureus in UHT milk at 12°C 120 100 80 60 40 20 0.930.940.950.960.970.98 Water activity (a w)w) FS0501 182000

19. NaCl and glucose concentrations and corresponding a w values at 25°C aWaW % w/w NaClGlucose 1.000.00 0.991.748.90 0.983.4315.74 0.966.5728.51 0.949.3837.83 0.9211.9043.72 0.9014.1848.54 0.8816.2853.05 0.8618.1858.45 FS0501 192000

20. Minimum levels of a W permitting growth at near optimum temperatures aWaW MouldsAspergillus chevalieri0.71 Aspergillus ochraceus0.78 Aspergillus flavus0.80 Penicillium verrucosum0.79 Fusarium moniliforme0.87 YeastsSaccharomyces rouxii0.62 Saccharomyces cerevisiae0.90 Bacteria Bacillus cereus0.92 Clostridium botulinum (proteolytic)0.93 Clostridium botulinum (non-proteolytic)0.97 Escherichia coli0.93 Salmonella0.95 Staphylococcus aureus0.83 FS0501 202000

21. Range of a W in foods and their microbial flora a w range > 0.98 0.93 - 0.98 FS0501 21 2000 foods Fresh meats Fresh fish Fresh fruits Fresh vegetables Canned vegetables in brine Canned fruit in light syrup (<3.5% salt, 26% sugar) Fermented sausages Processed cheese Bread Evaporated milk Tomato paste (10% salt, 50% sugar) microbial flora (C. perfringens, Salmonella) (Pseudomonas) (B. cereus, C. botulinum, Salmonella) lactobacilli, bacilli and micrococci

22. Range of a W in foods and their microbial flora a w range 0.85 - 0.93 0.6 - 0.85 < 0.6 FS0501 22 2000 foods Dry fermented sausages Raw ham (17% salt, saturated sucrose) Dried fruit Flour Cereals Salted fish Nuts Confectionery Honey Noodles Dried egg, milk microbial flora S. aureus Mycotoxin producing moulds Spoilage yeasts and moulds Xerophilic fungi Halophiles Osmophilic yeasts No growth but may remain viable

23. Factors affecting microbial growth Key messages Temperature, pH, water activity and oxygen tension are the principal factors affecting microbial growth There are optimum ranges for these parameters These optima are interdependent They can be selected to inhibit the growth of certain organisms within limits related to the palatability of food Certain foods are suited for the growth of certain flora FS0501 232000