1. Foodtecb 1 Food technologies to control the development of microbiological hazards Module 02 - Lecture 04b

2. Foodtecb 2 Technologies  temperature control  control of water activity  control of pH  control of redox potential  antimicrobial agents Technologies based on:

3. Foodtecb 3 Temperature HotCold C (Minimum) B (Optimum) A (Maximum) How temperature affects growth rate of a bacterial population

4. Foodtecb 4 Temperature range for growth of pathogens Temperature°C Min.Opt.Max. Salmonella 535 - 3747 Campylobacter 304247 E. coli 103748 S. aureus 6.537 - 4048 C. botulinum (proteolytic)1050 C. botulinum (non - proteolytic) 3.325 - 37 B. cereus 430 - 3548 - 50

5. Foodtecb 5 Temperature °C Min. Opt. Max. Penicillium verrucosum02031 Aspergillus ochraceus82837 Aspergillus flavus 103242 Fusarium moniliforme 32537 Temperature range for growth of toxigenic moulds

6. Foodtecb 6 0° 10° 36.5° 60° 72° 100° Boiling point Pasteurising temperature Freezer Fridge Body temperature Temperature zones SAFETY DANGER DANGER

7. Foodtecb 7  Water is required for the growth and metabolism of microorganisms  All the water in foods is not available for microorganisms  The degree of availability of water is measured by water activity (a w )  Chemical and enzymatic reactions are also affected by availability of water Water activity

8. Foodtecb 8 a w is the ratio of water vapour pressure of food (p) to that of pure water (p o ) at the same temperature. a w = p/ p o 0 < a w < 1 Water activity (definition)

9. Foodtecb 9 Water activity (3) 0.10.20.30.40.50.60.70.80. 9 AwAw Reaction rate Growth of: Moulds Yeasts Bacteria

10. Foodtecb 10 Minimum levels of a W permitting growth ( at near optimum temperatures ) MouldsAspergillus chevalieri 0.71 Aspergillus ochraceus 0.78 Aspergillus flavus 0.80 Penicillium verrucosum0.79 Fusarium moniliforme 0.87 YeastsSaccharomyces rouxii0.62 Saccharomyces cerevisiae 0.90 BacteriaBacillus cereus 0.92 Clostridium botulinum (proteolytic) 0.93 Clostridium botulinum (non-proteolytic) 0.97 Escherichia coli 0.93 Salmonella0.95 Staphylococcus aureus 0.83

11. Foodtecb 11 Range of a W in foods and their microbial flora a w rangeFoodsMicrobial flora > 0.98 Fresh meats Fresh fish Fresh fruits Fresh vegetables Canned vegetables in brine Canned fruit in light syrup (<3.5 % salt, 26% sugar) (C. perfringens, Salmonella) (Pseudomonas) 0.93 - 0.98 Fermented sausages Processed cheese Bread Evaporated milk Tomato paste (10% salt, 50% sugar) (B. cereus, C. botulinum, Salmonella) lactobacilli, bacilli and micrococci

12. Foodtecb 12 Range of a W in foods and their microbial flora a w rangeFoodsMicrobial flora 0.85 - 0.93 S. aureus Mycotoxin producing moulds Spoilage yeasts and moulds Dry fermented sausages Raw ham (17% salt, saturated sucrose) 0.6 - 0.85 Xerophilic fungi Halophiles Osmophilic yeasts Dried fruit Flour Cereals Salted fish Nuts < 0.6 No growth but may remain viable Confectionery Honey Noodles Dried egg, milk

13. Foodtecb 13 a w can be reduced by :  Removing water (drying)  Decreasing availability of water by crystalization (freezing)  Decreasing availability by binding water with water binding agents e.g. salt, sugar Water activity (4)

14. Foodtecb 14 a w 1.00 0.99 0.98 0.96 0.94 0.92 0.90 0.88 0.86 Concentration of NaCl and glucose at various a w values (at 25°C) % w / w glucose 0.00 8.90 15.74 28.51 37.83 43.72 48.54 53.05 58.45 % w / w NaCl 0.00 1.74 3.43 6.57 9.38 11.90 14.18 16.28 18.18

15. Foodtecb 15 Drying methods  sun drying  air drying  spray drying  freeze drying Examples of drying methods are :

16. Foodtecb 16 Drying rate (1) Drying rate depends on :  air velocity  surface area  air temperature  humidity of the air

17. Foodtecb 17 pH values limiting the growth of pathogens pH MinMax. Escherichia coli 4.48.5 Salmonella typhi 4 - 4.58 - 9.6 Bacillus cereus 4.99.3 Clostridium botulinum 4.68.5 Staphylococcus aureus 49.8 Saccharomyces cerevisiae 2.38.6 Aspergillus flavus2.011.2 Fusarium moniliforme2.510.7 Penicillium verrucosum2.010.0

18. Foodtecb 18 pH Acidification  addition of vinegar Fermentation  organic acid  competitive exclusion  antimicrobial agents

19. Foodtecb 19 pH of different foods Approximate pH ranges of some common food commodities 14 13 12 11 10 9 8 7 6 5 4 3 2 pH Fermented shark Egg white fish meat Citrus fruits milk Soft drinks flour vegetables beer

20. Foodtecb 20 Redox (E h ) low / negative: reducing medium high / positive: oxidizing medium E h = E o + RT / nF. (oxidant). H+ / (reductant) E h (mv)

21. Foodtecb 21 Redox (1) E h depends on :  availability of oxygen  ratio of oxidant and reductant  pH  poising capacity  microbial activity

22. Foodtecb 22 Redox and bacterial growth Obligate or strict aerobes: positive E h Obligate anaerobes: negative or low E h

23. Foodtecb 23 E h & pH values of foods E h & pH values of foods pH 5.7 5.9 6.5 6 7.0 6.0 6.2 4.2 E (mV) -200 +225 -20 to -150 -320 to -360 -225 -150 +74 +436 Raw meat Raw minced meat Cooked sausages and canned meats Wheat (whole grain) Barley (ground grain) Potatoe tuber Spinach Pear

24. Foodtecb 24 Control of E h  Vacuum packaging  Modified atmosphere packaging by gas flushing: CO 2, N 2

25. Foodtecb 25 Antimicrobial agents  Curing salts e.g nitrites  Bacteriocins e.g. nisin  Gas: e.g CO 2  Organic acids / salts e.g benzoic, sorbic and propionic acid

26. Foodtecb 26 Antimicrobial activity Depends on :  pH  lipid  microorganism

27. Foodtecb 27 Smoking Combination of several factors :  heat treatment  drying  antimicrobial agent in the smoke

28. Foodtecb 28 Combinations of food technologies Combined technologies  Milk pasteurization and aseptic packaging  Hurdle technologies  fermentation, smoking  Refrigerated processed food of extended durability (REPFED)