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Food technologiesFood technologiesto control the development of to control the development of
microbiological hazardsmicrobiological hazards
Module 02 - Lecture 04b
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TechnologiesTechnologies
temperature control control of water activity control of pH control of redox potential antimicrobial agents
Technologies based on:
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TemperatureHotCold
C (Minimum)
B (Optimum)
A (Maximum)
How temperature affects growthrate of a bacterial population
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Temperature rangeTemperature rangefor growth of pathogensfor growth of pathogens
Temperature°C
Min. Opt. Max.
Salmonella 5 35 - 37 47Campylobacter 30 42 47E. coli 10 37 48S. aureus 6.5 37 - 40 48C. botulinum (proteolytic) 10 50C. botulinum (non - proteolytic) 3.3 25 - 37B. cereus 4 30 - 35 48 - 50
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Temperature °C Min. Opt. Max.
Penicillium verrucosum 0 20 31
Aspergillus ochraceus 8 28 37
Aspergillus flavus 10 32 42
Fusarium moniliforme 3 25 37
Temperature range for growthTemperature range for growthof toxigenic mouldsof toxigenic moulds
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0°
10°
36.5°
60°
72°
100°Boilingpoint
Pasteurisingtemperature
Freezer
Fridge
Bodytemperature
Temperature zonesTemperature zones
SAFETY SAFETY
SAFETY SAFETY
DANGERDANGER
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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 activityWater activityWater activityWater activity
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a w is the ratio of water vapour pressure of food (p) to that of pure water (po) at the
same temperature.
a w = p/ po
0 < a w < 1
Water activity Water activity (definition)(definition)Water activity Water activity (definition)(definition)
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Water activity Water activity (3)(3)Water activity Water activity (3)(3)
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Aw
Reactionrate
Growth of:
MouldsYeasts
Bacteria
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Minimum levels of aMinimum levels of aW W permitting growth permitting growth
( ( at near optimum temperatures )at near optimum temperatures )
Moulds Aspergillus chevalieri 0.71Aspergillus ochraceus 0.78Aspergillus flavus 0.80Penicillium verrucosum 0.79Fusarium moniliforme 0.87
Yeasts Saccharomyces rouxii 0.62Saccharomyces cerevisiae 0.90
Bacteria Bacillus cereus 0.92Clostridium botulinum (proteolytic) 0.93Clostridium botulinum (non-proteolytic) 0.97Escherichia coli 0.93Salmonella 0.95Staphylococcus aureus 0.83
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Range of aRange of aWW in foods in foods
and their microbial floraand their microbial flora
aw range Foods Microbial flora
> 0.98
Fresh meatsFresh fishFresh fruitsFresh vegetablesCanned vegetables in brine Canned fruit in light syrup (<3.5 % salt, 26% sugar)
(C. perfringens, Salmonella)
(Pseudomonas)
0.93 - 0.98 Fermented sausagesProcessed cheeseBreadEvaporated milkTomato paste(10% salt, 50% sugar)
(B. cereus,C. botulinum,Salmonella)lactobacilli, bacilli andmicrococci
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Range of aRange of aWW in foods in foods
and their microbial floraand their microbial flora
aw range Foods Microbial flora
0.85 - 0.93 S. aureus
Mycotoxin producing mouldsSpoilage yeasts and moulds
Dry fermented sausagesRaw ham (17% salt, saturated sucrose)
0.6 - 0.85Xerophilic fungi
HalophilesOsmophilic yeasts
Dried fruitFlourCerealsSalted fishNuts
< 0.6 No growth but may remain viable
ConfectioneryHoneyNoodlesDried egg, milk
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aw 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 Water activity (4)(4)Water activity Water activity (4)(4)
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aw
1.000.990.980.960.940.920.900.880.86
Concentration of NaCl and glucose Concentration of NaCl and glucose at various aat various aww values (at values (at 25°C)25°C)
% w / w
glucose
0.008.90
15.7428.5137.8343.7248.5453.0558.45
% w / w
NaCl
0.001.743.436.579.38
11.9014.1816.2818.18
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Drying methodsDrying methodsDrying methodsDrying methods
sun drying
air drying
spray drying
freeze drying
Examples of drying methods are :
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Drying rate Drying rate (1)(1)Drying rate Drying rate (1)(1)
Drying rate depends on :
air velocity
surface area
air temperature
humidity of the air
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pH values limiting the growth pH values limiting the growth of pathogensof pathogens
pH
Min Max.
Escherichia coli 4.4 8.5Salmonella typhi 4 - 4.5 8 - 9.6Bacillus cereus 4.9 9.3Clostridium botulinum 4.6 8.5Staphylococcus aureus 4 9.8Saccharomyces cerevisiae 2.3 8.6Aspergillus flavus 2.0 11.2Fusarium moniliforme 2.5 10.7Penicillium verrucosum 2.0 10.0
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pHpHpHpH
Acidification addition of vinegar
Fermentationorganic acidcompetitive exclusionantimicrobial agents
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pH of different foodspH of different foodspH of different foodspH of different foods
Approximate pH ranges of some
common food commodities1413121110 9 8 7 6 5 4 3 2
pH
Fermented shark
Egg white
fish
meat
Citrus fruits
milk
Soft drinks
flourvegetables
beer
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Redox (ERedox (Ehh))Redox (ERedox (Ehh))
low / negative: reducing medium
high / positive: oxidizing medium
Eh = Eo + RT / nF . (oxidant) . H+ / (reductant)
E h (mv)
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Redox Redox (1)(1)Redox Redox (1)(1)
Eh depends on :
availability of oxygenratio of oxidant and
reductant
pH
poising capacity
microbial activity
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Redox and bacterial growthRedox and bacterial growth Redox and bacterial growthRedox and bacterial growth
Obligate or strict aerobes:
positive Eh
Obligate anaerobes:
negative or low Eh
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EEh h & pH values of foods & 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
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Control of E Control of E h h Control of E Control of E h h
Vacuum packaging
Modified atmosphere packaging by gas flushing: CO2 , N2
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Antimicrobial agentsAntimicrobial agentsAntimicrobial agentsAntimicrobial agents
Curing salts e.g nitrites Bacteriocins e.g. nisin
Gas: e.g CO2
Organic acids / salts e.g benzoic, sorbic and propionic acid
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Antimicrobial activityAntimicrobial activityAntimicrobial activityAntimicrobial activity
Depends on :
pH
lipid
microorganism
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SmokingSmokingSmokingSmoking
Combination of several factors :
heat treatment drying antimicrobial agent in the smoke
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Combinations of Combinations of food technologiesfood technologies
Combined technologies
Milk pasteurization and aseptic packaging
Hurdle technologies fermentation,
smoking
Refrigerated processed food of extended durability (REPFED)