Intrinsic Parameters Flashcards
intrinsic parameters
aw pH Redox potential Nutrient content Vitamins Antimicrobial constituents biological structures competitive microflora
Water activity (aw)
- Moisture content
- Ratio of water vapor pressure of pure water at the same temperature
aw formula
P/Po
P = vapor pressure of solution
Po = vapor pressure of solvent
Relative Humidity
100 x aw
Common aw values
Pure water: 1.00
22% NaCl: 0.86
Fresh food: >0.99
Min aw value for microbial growth: bacteria
0.90
Min aw value for microbial growth: yeast
0.88
Min aw value for microbial growth: mold
0.80
Low aw:
Increases lag phase
Decreases growth rate
Decreases max population
aw lowering food additives
NaCl
KCl
Carbs
Phosphates
growth decreases as…
aw decreases
Best microbial growth pH level:
6.0 - 7.5
Few organisms grow at pH below
4.0
No growth of C. botulinum at or below
4.6
Butter pH
6.1 - 6.4
Milk
6.3 - 6.5
Fish
6.6 - 6.8
Beef
5.1 - 6.2
Chicken
6.2 - 6.4
Buffering capacity: meat
High
Buffering capacity: produce
low
Oxidation
Loss of an electron
Addition of O2
Reduction
Gain of electrons
Removal of O2
Reducing agent
Substance that gives up electrons or acquires O2
Oxidizing agent
Substance that acquires electrons or gives up O2
Nutrient content
- water (aw)
- Energy source (sugar, alcohol, AA)
- Nitrogen source (protein)
Vitamins
- Needed by gram+ bacteria
- Synthesized by gram- bacteria & mold
Antimicrobial constituents
Spices
-Eugenol (cinnamon)
-Allicin (garlic)
-Thymol (oregano)
Enzymes
-lactoferrin (milk)
-lysozyme (egg)Biological structures
outer coverings: Skin (fruits), hide (animals), shell (nuts, eggs)
