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38 Cards in this Set

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  • Back
What are four basic ways in which microbes can be controlled in food?
- prevent contamination
- remove them
- kill them (bactericidal)
- prevent gowth (bacteriostatic)
What are some parameters we can change (intrinsic/extrinsic) to control microbes in food
Low aw, pH, and T
High T, irradiation, MAP
How freezing affect microbes?
Water activity is low. Freezing does not kill generally (though freeze-thaw cycles lethal)
• ice crystals discrupt cell structure
• macromolecules can be denatured/destabilized
General effects of low T, pH, aw on microbes?
Stops or reduces growth rate
Enzyme activity reduced
Spore germination prevented
effect of viability
How does low T affect microbial growth?
Slows enzymes and metabolic activity
How does low aw affect microbes?
Enzyme inhibition
Osmotic Shock
Plasmolyis --> water migration out of cell causing dehydration
How does low pH affect microbes?
Energy expended as cell attempts to remove H+; eventual cell death
How does high T affect microbes?
Denatures proteins
Breaks DNA strands
Cell membrane disruption
RNA degradation
Who invented canning?
Nicholas Appert
Durand altered process to use metal can
What is pasteurization?
High T processing - goal is 5D reduction; legal for milk is 5D though usually done to 7D

Does not kill spores -- main goal is killing of pathogens/spoilage organisms
What are the T's/times of
HTST: 15 sec @ 161F
LTLT: 30 min @ 145F
eggs: 100 min @ 136F - goal w/eggs is to kill salmonella but not cook egg
What is commercial sterilization?
Heat treat to rid food pf pathogens and mesophilic organisms:
100-150C/ Canning @ 121C
What are the conditions of UHT?
1-2 seconds at about 150C
What are the disadvantages to commercial sterilization?
It affects food sensory qualities and nutritional value
What is the Aw/pH cutoff for low acid/ acidic foods?
aw = 0.85
pH <4.6
What is lyophilization?
Freeze drying
-> freezes and dehydrates
Besides T, what are the most important factors in controlling microbes in food?
aw, pH, and O2 concentration
What organisms are used to design thermal processing conditions?
There are four:
Clost. botulinum
Clost. sporogenes*
Clost. theromsaccrolyticum
Bacillus stearothermophilus
Thermal death rate follows what kintects? Write the basic formula
First order
What is D?
Decimal reduction time
The time to reduce the microbe count by one log = 1/10

D = time/log(N/N0)
What is D(121) for C. botulinum?
0.204 min

So for canning, 12D = 12*0.204 = 2.45min
How do the D-values of organisms compare?
sporeformers >> veg. cells
What influences D?
The environment! pH, aw.. as these are lowered, D-values go down. D-values are specific to the food.
What is the "Z" value?
The rise in temperature needed to reduce D by a factor of 10.

I.e. if we want D = .2 min instead of 2 min, how much hotter??

It's a measure of the sensitivity of the microbe to changes in T
How is Z calculated?
Z = delta-T/log(D1/D2)
What is F?
The actual time required to reduce the microbial load by a specific amount in a specific food at a specific temperature.
What is Fo?
Also called the "sterilization value" - it's a reference for 121C and z=10C
Botulinum often cited:
F0=2.45 min

but canned F=4*fo=10-12min
What is the calculation for an equivalent Temp?
T2 = F0/(10^((T2-121)/Z))
How is wet heat different from dry heat in microbial reduction?
Wet heat more effective
Wet: kills by denaturation of DNA, proteins, enzymes
Dry: kills by dehydration/oxidation
What is a microbiological criterion?
A standard, guideline, or specification that defines food acceptability based on the absence/presence and/or number of microbes per unit.
What is the difference between standard/guideline/specification?
At what point it's applied and if the government involved
What is a standard?
A mandatory criterion outlined by the government. I.e. listeria zero-tolerance
What is a guideline?
A recommendation put forth by some agency (FDA/USDA) - advisory critereon
What is a specification?
An agreed upon criterion between a buyer/supplier. Part of a "product spec"
Why adopt these criterion?
For many reasons:
The liklihood that the food will support growth
Who the food's primary consumer will be
what the processing conditions are going to be
if there is evidence that there is a health hazard
how the food will be cooked before consumption
if there are suitable tests
What are the main components of a criteria?
1. Identification of the microbe of interest/why it's an issue
2. Specification of the appropriate test
3. Sampling methods (n)
4. Limits (m and M)
5. Acceptably positives (n-c)
What is a "case"
It categorized the severity of the potential hazard of the microbe in the food: 1-15

If = 15
n=60 c=0
What is n? m? M? c?
n = number of analytical units (samples) to be tested
m = min number for it to be counted as a positive
M = max number allowed - i.e. positives are allowed unles ANY exceed M
c = the number of positives allowed