Transcript Food technologies to control the development of microbiological hazards

Module 02 - Lecture 04b
Food technologies
to control the development of
microbiological hazards
Foodtecb 1
Technologies
Technologies based on:
 temperature control
 control of water activity
 control of pH
 control of redox potential
 antimicrobial agents
Foodtecb 2
How temperature affects growth
rate of a bacterial population
B (Optimum)
C (Minimum)
Cold
Temperature
Foodtecb 3
A (Maximum)
Hot
Temperature range
for growth of pathogens
Temperature°C
Salmonella
Campylobacter
E. coli
S. aureus
C. botulinum (proteolytic)
C. botulinum (non - proteolytic)
B. cereus
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Min.
Opt.
Max.
5
30
10
6.5
10
3.3
4
35 - 37
42
37
37 - 40
47
47
48
48
50
25 - 37
48 - 50
30 - 35
Temperature range for growth
of toxigenic moulds
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
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Temperature zones
Boiling
point
100°
SAFETY
SAFETY
Pasteurising
temperature
72°
60°
Body
temperature
Fridge
Freezer
Foodtecb 6
36.5°
DANGER
10°
0°
SAFETY
SAFETY
Water activity
 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
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Water activity (definition)
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<aw<1
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Water activity (3)
Reaction
rate
Growth of:
Moulds
Yeasts
Bacteria
0.1
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0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.
9
Aw
Minimum levels of aW permitting growth
( at near optimum temperatures )
Moulds
Yeasts
Bacteria
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Aspergillus chevalieri
Aspergillus ochraceus
Aspergillus flavus
Penicillium verrucosum
Fusarium moniliforme
Saccharomyces rouxii
Saccharomyces cerevisiae
Bacillus cereus
Clostridium botulinum (proteolytic)
Clostridium botulinum (non-proteolytic)
Escherichia coli
Salmonella
Staphylococcus aureus
0.71
0.78
0.80
0.79
0.87
0.62
0.90
0.92
0.93
0.97
0.93
0.95
0.83
Range of aW in foods
and their microbial flora
aw range
Foods
> 0.98
Fresh meats
Fresh fish
Fresh fruits
Fresh vegetables
Canned vegetables
in brine
Canned fruit
in light syrup
(<3.5 % salt, 26% sugar)
0.93 - 0.98
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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
Range of aW in foods
and their microbial flora
aw range
Foods
Microbial flora
0.85 - 0.93
Dry fermented
sausages
Raw ham
(17% salt,
saturated sucrose)
S. aureus
0.6 - 0.85
< 0.6
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Dried fruit
Flour
Cereals
Salted fish
Nuts
Confectionery
Honey
Noodles
Dried egg, milk
Mycotoxin
producing moulds
Spoilage yeasts
and moulds
Xerophilic fungi
Halophiles
Osmophilic yeasts
No growth but
may remain viable
Water activity (4)
aw can be reduced by :



Foodtecb 13
Removing water (drying)
Decreasing availability of water by
crystalization (freezing)
Decreasing availability by binding water with
water binding agents e.g. salt, sugar
Concentration of NaCl and glucose
at various aw values (at 25°C)
Foodtecb 14
aw
%w/w
NaCl
%w/w
glucose
1.00
0.99
0.98
0.96
0.94
0.92
0.90
0.88
0.86
0.00
1.74
3.43
6.57
9.38
11.90
14.18
16.28
18.18
0.00
8.90
15.74
28.51
37.83
43.72
48.54
53.05
58.45
Drying methods
Examples of drying methods are :
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
sun drying

air drying

spray drying

freeze drying
Drying rate (1)
Drying rate depends on :
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
air velocity

surface area

air temperature

humidity of the air
pH values limiting the growth
of pathogens
pH
Escherichia coli
Salmonella typhi
Bacillus cereus
Clostridium botulinum
Staphylococcus aureus
Saccharomyces cerevisiae
Aspergillus flavus
Fusarium moniliforme
Penicillium verrucosum
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Min
Max.
4.4
4 - 4.5
4.9
4.6
4
2.3
2.0
2.5
2.0
8.5
8 - 9.6
9.3
8.5
9.8
8.6
11.2
10.7
10.0
pH
Acidification
 addition of vinegar
Fermentation
 organic acid
 competitive exclusion
 antimicrobial agents
Foodtecb 18
pH of different foods
pH
14
13
12
11
10
9
8
7
6
5
4
3
2
Foodtecb 19
Approximate pH ranges of some
common food commodities
Fermented shark
Egg white
fish
milk
vegetables
meat
Citrus fruits
flour
Soft drinks
beer
Redox (Eh)
E h (mv)
low / negative: reducing medium
high / positive: oxidizing medium
Eh = Eo + RT / nF . (oxidant) . H+ / (reductant)
Foodtecb 20
Redox (1)
Eh depends on :


Foodtecb 21
availability of oxygen
ratio of oxidant and
reductant

pH

poising capacity

microbial activity
Redox and bacterial growth
Obligate or strict aerobes:
positive Eh
Obligate anaerobes:
negative or low Eh
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Eh & pH values of foods
Raw meat
Raw minced meat
Cooked sausages and
canned meats
Wheat (whole grain)
Barley (ground grain)
Potatoe tuber
Spinach
Pear
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E (mV)
pH
-200
+225
-20 to -150
5.7
5.9
6.5
-320 to -360
-225
-150
+74
+436
6
7.0
6.0
6.2
4.2
Control of E h
 Vacuum packaging
 Modified atmosphere packaging by
gas flushing: CO2 , N2
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Antimicrobial agents
 Curing salts e.g nitrites
 Bacteriocins e.g. nisin
 Gas: e.g CO2
 Organic acids / salts e.g benzoic,
sorbic and propionic acid
Foodtecb 25
Antimicrobial activity
Depends on :
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
pH

lipid

microorganism
Smoking
Combination of several factors :



Foodtecb 27
heat treatment
drying
antimicrobial agent in the smoke
Combinations of
food technologies
Combined technologies


Milk pasteurization and aseptic
packaging
Hurdle technologies
 fermentation, smoking

Foodtecb 28
Refrigerated processed food of
extended durability (REPFED)