Micro - Final: Control/death/criterion Of Microbes

Front 1

What are four basic ways in which microbes can be controlled in food?

Back 1

- prevent contamination
- remove them
- kill them (bactericidal)
- prevent gowth (bacteriostatic)

Front 2

What are some parameters we can change (intrinsic/extrinsic) to control microbes in food

Back 2

Low aw, pH, and T
High T, irradiation, MAP
Antimicrobials

Front 3

How freezing affect microbes?

Back 3

Water activity is low. Freezing does not kill generally (though freeze-thaw cycles lethal)
• ice crystals discrupt cell structure
• macromolecules can be denatured/destabilized

Front 4

General effects of low T, pH, aw on microbes?

Back 4

Stops or reduces growth rate
Enzyme activity reduced
Spore germination prevented
effect of viability

Front 5

How does low T affect microbial growth?

Back 5

Slows enzymes and metabolic activity

Front 6

How does low aw affect microbes?

Back 6

Enzyme inhibition
Osmotic Shock
Plasmolyis --> water migration out of cell causing dehydration

Front 7

How does low pH affect microbes?

Back 7

Energy expended as cell attempts to remove H+; eventual cell death

Front 8

How does high T affect microbes?

Back 8

Denatures proteins
Breaks DNA strands
Cell membrane disruption
RNA degradation

Front 9

Who invented canning?

Back 9

Nicholas Appert
Durand altered process to use metal can

Front 10

What is pasteurization?

Back 10

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

Front 11

What are the T's/times of
HTST
LTLT
eggs

Back 11

HTST: 15 sec @ 161F
LTLT: 30 min @ 145F
eggs: 100 min @ 136F - goal w/eggs is to kill salmonella but not cook egg

Front 12

What is commercial sterilization?

Back 12

Heat treat to rid food pf pathogens and mesophilic organisms:
100-150C/ Canning @ 121C

Front 13

What are the conditions of UHT?

Back 13

1-2 seconds at about 150C

Front 14

What are the disadvantages to commercial sterilization?

Back 14

It affects food sensory qualities and nutritional value

Front 15

What is the Aw/pH cutoff for low acid/ acidic foods?

Back 15

aw = 0.85
pH <4.6

Front 16

What is lyophilization?

Back 16

Freeze drying
-> freezes and dehydrates

Front 17

Besides T, what are the most important factors in controlling microbes in food?

Back 17

aw, pH, and O2 concentration

Front 18

What organisms are used to design thermal processing conditions?

Back 18

There are four:
Clost. botulinum
Clost. sporogenes*
Clost. theromsaccrolyticum
Bacillus stearothermophilus

Front 19

Thermal death rate follows what kintects? Write the basic formula

Back 19

First order
N=No*e^(-kt)

Front 20

What is D?

Back 20

Decimal reduction time
The time to reduce the microbe count by one log = 1/10

D = time/log(N/N0)

Front 21

What is D(121) for C. botulinum?

Back 21

0.204 min

So for canning, 12D = 12*0.204 = 2.45min

Front 22

How do the D-values of organisms compare?

Back 22

sporeformers >> veg. cells

Front 23

What influences D?

Back 23

The environment! pH, aw.. as these are lowered, D-values go down. D-values are specific to the food.

Front 24

What is the "Z" value?

Back 24

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

Front 25

How is Z calculated?

Back 25

Z = delta-T/log(D1/D2)

Front 26

What is F?

Back 26

The actual time required to reduce the microbial load by a specific amount in a specific food at a specific temperature.

Front 27

What is Fo?

Back 27

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

Front 28

What is the calculation for an equivalent Temp?

Back 28

T2 = F0/(10^((T2-121)/Z))

Front 29

How is wet heat different from dry heat in microbial reduction?

Back 29

Wet heat more effective
Wet: kills by denaturation of DNA, proteins, enzymes
Dry: kills by dehydration/oxidation

Front 30

What is a microbiological criterion?

Back 30

A standard, guideline, or specification that defines food acceptability based on the absence/presence and/or number of microbes per unit.

Front 31

What is the difference between standard/guideline/specification?

Back 31

At what point it's applied and if the government involved

Front 32

What is a standard?

Back 32

A mandatory criterion outlined by the government. I.e. listeria zero-tolerance

Front 33

What is a guideline?

Back 33

A recommendation put forth by some agency (FDA/USDA) - advisory critereon

Front 34

What is a specification?

Back 34

An agreed upon criterion between a buyer/supplier. Part of a "product spec"

Front 35

Why adopt these criterion?

Back 35

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

Front 36

What are the main components of a criteria?

Back 36

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)

Front 37

What is a "case"

Back 37

It categorized the severity of the potential hazard of the microbe in the food: 1-15

If = 15
n=60 c=0

Front 38

What is n? m? M? c?

Back 38

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