Transcript D-ChemistryofWater

Meat Chemistry - Importance of
Compositional Components and
Chemistry of Each in Processed Meats
1. Water
– present in greatest quantity in meat and most
products
– important to: 1) eating quality, and 2)
economics
– remember: water is both a meat component
and a non-meat (added) ingredient
Functions of water
a. palatability
– juiciness
– initial juiciness impression
– contributes to tenderness
b. yields / economics
– must provide for the water expected to be lost
in cooking
– binding mechanisms for water become
important to yields
c. universal solvent
– dispersion and distribution of ingredients
i.e. nitrite
– 3% added water allowed in fresh sausage
“to facilitate mixing”
– also critical as a protein solvent
d. temperature control
– improved protein solubility
– bacterial control
– thermal capacity, especially ice, is very large
Thermal capacity
Specific heat of water - 1 BTU/lb/oF
ice - 0.5 BTU / lb/oF
latent heat of crystallization - 144 BTU/lb
(energy required to melt ice (or freeze water)
without a temperature change)
Example of effects:
10 lbs of cold (32oF) water added to frankfurter emulsion
chopped from 32oF to 55oF
= 10 lbs x 23oF x 1 BTU/lb/oF = 230 BTU
Thermal capacity (continued)
Specific heat of water - 1 BTU/lb/oF
ice - 0.5 BTU/lb/oF
latent heat of crystallization - 144 BTU/lb
Example of effects:
10 lbs of ice (32oF) added to emulsion at 32oF & chopped to 55oF
= 10 lbs x 144 BTU/lb = 1440 BTU (conversion to water)
plus 10 lbs x 23oF x 1 BTU/lboF = 230 BTU
1670 BTU
(over 7 x that of cold water alone)
Temperature control is a major advantage
to using frozen meat but frozen meat has
less functional protein and thermal capacity
is less than ice
Thermal capacity of meat 0.8 BTU/lb/oF (fresh)
0.4 BTU/lb/oF (frozen)
Water in meat systems
– Bound by proteins
– In order to understand water in meat
systems it is necessary to understand:
water : protein interactions
- andwater : water interactions
Water is a unique compound with a
unique structure:
H2O
two positive poles
+H
H+
O
-
and
two negative poles
-
(think 3-dimensional tetrahedron)
Structure and charged poles create
intermolecular “H bonding”
– Each molecule binds 4 others --one at each pole
therefore
water attracts water
= water : water interaction
Meat also has a variety of polar
groups --- due to proteins
– this is a critical property of proteins
and is a unique “fingerprint” for
each protein.
– Why?
Proteins are composed of amino acids
– amino acids each have polar / nonpolar properties and charges
– combination of amino acids
determines protein properties such
as protein : water interaction
NH2
R
C
H
COOH
Meat proteins first bind water directly
to the charged amino acid groups
– This is a small amount of water
 5 - 10 g/100 g protein
– very tightly bound
“Bound water”
Bound water attracts other water
molecules
– Another 2 - 3 molecule layer around
protein groups (50 - 60 g/100 g protein)
= “Immobilized water”
Bound water and immobilized water
are considered as one in terms of
water movement and changes in meat
products.
Which leaves water attracted weakly
to the bound and immobilized water.
= “Free water” (~ 300 g/100 g protein)
“Free” water is loosely held and very
dependent upon capillary space
between and within proteins.
Muscle structure therefore becomes a
determinant of water binding ability
Anything which will alter protein
structure and spacing will affect water
retention
Remember that this is 3dimensional…
Thus, it is myofibrillar proteins that
are most important ----- have most
polar and charged amino acids.
70 -75% - myofibrillar
~ 20%
- sarcoplasmic
< 10%
- stromal (connective tissue)
This is why lean muscle is most desirable for
processed meats.
- and we need to know how to manipulate proteins
to change water binding
Three fundamental ways to manipulate
water binding ability of meat
1. pH
- concentration of H+
2. Salt
Na+ Cl–
3. Phosphates
PO4 (– = )
Effects of pH on water binding
– water binding is minimal at about
pH 5.0 - 5.2
– water binding increases above or
below this pH
protein
–
+
pH 6.0
–
–
–
+
+
–
–
net charge = –3
+3H +
protein
–
H+
+
pH 5.1
–
–
–
+
+
– +H
H+
–
net charge = 0
Isoelectric Point
+2H +
protein
H+
–
H+
+
pH 4.5
–
H+
–
–
+
– H+
+ H+–
net charge = +2
+
+
H2O
pH 6.0
H2O
pH 5.1
+
+
H2O
pH 4.5
Note: Isoelectric Point [Know this!]
– pH at which charge on protein = 0
– minimum water binding
– dependent on amino acid composition
i.e. will be different for different proteins
Effects of salt on water binding
– Shifts isoelectric point curve to the
left
– raises water binding at all typical
meat pH’s
protein
–
+
pH 6.0
–
–
–
+
+
–
–
net charge = 3
+ Na Cl
Na+
protein
–
+
pH 6.0
Cl ¯
–
–
+ Cl ¯ –
–
Cl ¯ +
–
net charge = –5
Note:
– salt increases the net negative charge on
meat proteins which increases protein
repulsion and water binding
– because more H+ are needed to
completely neutralize the negative
charges, the pH must be lower to reach
the isoelectric point
Effects of phosphates on water binding
– phosphates are basic and raise the pH of
meat
– phosphates are anions (-) and may create
a chloride effect on charges
– solubilize structural proteins to “loosen”
myosin and actin
Effects of Phosphates(cont’d)
– chelate cations such as Ca++ that can
crossbridge proteins
protein
+
–
–
–
+
Ca
+
+ –
–
–
–
–
+
+
After pH, salt and phosphate effects are
maximized, then other ingredients can be
considered for further increases in water
binding
i.e. proteins:
soy
whey
caseinate
collagen
carbohydrates: corn syrup
maltodextrins
starch
hydrocolloids: carrageenan
xanthan gum
Measurement of water holding capacity
(WHC)
1. Drip loss
– suspend intact muscle sample inside bag or container
– measure drip weight/drip loss after fixed time period
2. Press method
– sample placed on dried filter paper and submitted to
pressure between two plates
– separated “water ring” measured with planimeter.
– Ratio of water ring area to meat ring area is a relative
measure of WHC
Measurement of water holding capacity
(WHC) (continued)
3. Centrifuge method
– muscle sample or blended sample (with water, salt, etc.)
centrifuged and separated water measured.
4. Yields after heating
– samples heated at fixed time/temperature
– weight loss/water loss measured
5. Nuclear magnetic resonance (NMR)
– measures relative “freedom” of water molecules to
move in magnetic field
Increasing WHC is not always desirable
i.e. dry sausage, jerky, etc.
Concerns for water
1. Hard water
– decreases WHC due to minerals Mg++, Fe++, etc.
– may reduce effectiveness of phosphates - reaction
with mineral cations
– may cause product discoloration Fe++, Cu+, NO3– may induce rancidity developments from metals
like Fe++ or Cu+
– can induce “scum” when making injection “pickle”
and make other ingredients such as phosphates
hard to dissolve
Hard water = 10 grains/gal or more
(175 pmm)
Ames ground water = 24 grains/gal
2. Nitrate can be a health risk at 10 ppm
or more especially for babies
– methemoglobinemia
3. Water cleanliness (bacteria, etc.)
-cross-contamination of lines
-backflow from outlets
-ice machines
-dead-end lines