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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)