Fat/Lipids
– Second most abundant component (after water) in
meat --- by far the most variable
– composed of:
1.) neutral lipids (triglyceride) ~ 99% of meat/muscle lipids
Glycerol
H
|
H  C  OH
|
H  C  OH
|
H  C  OH
|
H
Plus…...
.…..3 fatty acids
Most are 14 - 20 carbon chains that are:
saturated (no double bonds),
monounsaturated (one double bond) or
polyunsaturated (multiple double bonds)
Fatty acids most often found in animal fats are:
oleic (c18:1)
palmitic (c16)
stearic (c18)
linoleic (c18:2)
myristic (c14)
palmitoleic (c16:1)
linolenic (c18:3)
arachidonic (c20:4)
40 – 50%
20 – 30%
10 – 15%
2 – 25%
1 – 5%
3 – 6%
< 1%
< 1%
Triglyceride:
H
O
|
||
H  C  O  C  R1
|
O
H  C  O  C  R2
|
O
H  C  O  C  R3
|
H
myristic….
palmitic*..
palmitoleic
stearic*….
oleic*…...
linoleic.….
linolenic....
arachidonic
Also:
2.) phospholipids ~ 1% of meat / muscle lipid
H
O
|
||
H  C  O  C  R1
|
O
H  C  O  C  R2
|
O
H  C  O  P  O  CH2  CH2  N(CH3)3
|
|
H
OH

(phosphatidylcholine)
– small quantity (~ 1%) in meat lipids but important to rancidity
because rancidity often begins with the phospholipids (located
in cell membranes)
Lipid/fat characteristics important to
meat processing
1. Softness - melting point
a. dependent on fatty acid chain length
– measured by saponification number
= mg KOH that reacts per g. of fat
H
O
|
||
H  C  O  C  R1
|
O
H  C  O  C  R2
|
O
H  C  O  C  R3
|
H
+ 3KOH
H
|
HC OH
|
H  C  OH
|
H  C  OH
|
H
O
+
3
K+ ¯O  C  R
fatty acid
glycerol
– a large saponification number indicates short
chain fatty acids
Softness/melting point
b. dependent on number of double bonds
– measured by iodine number
= grams of iodine (I2) which reacts with 100 g. of fat
(C – C = C – C) + I2  C – C – C – C
|
|
I
I
– a large iodine number indicates a large number of double
bonds (more unsaturated fatty acids)
– unsaturated fatty acids are source of rancid flavor
compounds as a result of oxidative rancidity
2. Free fatty acids
– Can be flavor problem if short chained
– i.e. butter
– may become problem in deep fat frying with
reuse of oil/fat
– should be less that 0.05% - 0.1% - at ~ 1% may
become organoleptically detectable
– “smoke point” for frying oil/fat --- lowest temperature
at which it will emit smoke -- free fatty acids make
smoke more likely
– free fatty acids in meat are not flavorful but are
more likely to become rancid
3. Breakdown products of fat which
indicate flavor problems
a. Peroxides – result of reaction of oxygen with fatty acids
– measurement indicates likelihood of rapid
development of rancid flavor
– peroxide value
= mg. peroxide oxygen per kg. of sample
b. aldehydes/ketones
– actual “rancid flavor” compounds
– many different ones are formed at different stages
of rancidity
– most common measurement for meat product
rancidity
– malonaldehyde
– measured by reaction with thiobarbituric acid (remember ?)
to give:
TBA number = mg. malonaldehyde/kg sample
– also are some other compounds which react with TBA
thus often referred to as thiobarbituric acid reactive
substances - TBARS
4. Fat/lipid is important to palatability
– flavor
– juiciness
– texture
5. Structural component
– i.e. emulsions/batters related to texture and
mouthfeel
6. economics
-fat is a cheap ingredient
7. nutritional
– essential fatty acids and fat soluble vitamins are
requirements
– linoleic, alpha-linoleic are essential to synthesize other
fatty acids
– conjugated linoleic acid (CLA) seems to have
significant health benefits
–  fat deposition,  lean muscle
– antioxidant
– reduction of cancer risks
– medium chain tryglycerides
– 6,8,10,12 carbon fatty acids
– transported directly to liver for metabolism therefore behave
like carbohydrates
i.e. increase energy, fat loss, lean muscle mass
– concerns for cholesterol (?)
– fat tissue not a major source
– trans fatty acids (by-product of hydrogenated
vegetable oils)
H
C-C-C-C = C -C-CH
– resemble saturated fatty acids in metabolism (increased risk
of coronary heart disease)
– common form in animal fat is cis
H H
C-C-C-C = C-C-C-C
Major practical concern for fat is rancidity
and its’ development
– must be controlled
– source of flavor “loss of freshness”
– “warmed-over” flavor in cooked meat
– occurs in all species but most rapid in poultry and
especially fish
– cholesterol oxidation/peroxides, other oxidation
products may be significant health risks by
themselves
Development of rancidity
1.) enzymatic
2.) hydrolytic
release of free fatty acids from glycerol
– important in butter (short chain fatty acids)
– free fatty acids in meat become more likely to react
with oxygen for oxidative rancidity
3.) oxidative rancidity (auto-oxidation)
– oxygen reacting with unsaturated fatty acids to
produce aldehydes and ketones
Auto - oxidation sequence
1.) Initiation
– extraction of H+ from fatty acid to form a
free radical R •
catalyst
R (fatty acid) 
R•
free radical
+ H+
– Slow, rate - limiting step
– Often involves phospholipids
– critical point - requires catalyst
a. metals - Fe, Cu, etc.
– water sources
– iron in meat pigment as Fe+++ (metmyoglobin)
– salt contaminants
b. light
c. accelerated by increased temperature
Auto - oxidation sequence
2.) Propagation
– free radical reacts quickly and easily with oxygen to
form hydroperoxy radical
–
R • + O2
free radical

ROO •
hydroperoxy radical
– very unstable, very reactive radical
– will attack fatty acid double bonds to get a H+ for
better stability
but ….
…..In doing so produces another free radical and a
hydroperoxide
ROO • + R

ROOH
hydroperoxide
+
R•
free radical
Second free radical then reacts with oxygen to
form hydroperoxy which again attacks a fatty
acid…………
Automatic cycle once begun therefore called
auto-oxidation
Each single free radical produced results in 500
more in this automatic cycle.
Each of the 500 create an additional 500
i.e. 500 x 500 = 250,000 x 500 = 125,000,000
etc.
thus auto-oxidation is a self-accelerating process
The hydroperoxide (ROOH) breaks down into
aldehyde and ketones giving the nasty flavors
and odors of rancid products
Each turn through the cycle turns out more
aldehydes and ketones so rancidity gets
progressively worse
3. Termination of the sequence
– Radicals can “run into each other,” react and
terminate the cycle, but usually not until several
times (~ 500) through the sequence.
Control points for auto-oxidation rancidity
1. fatty acid saturation
2. Avoid raw materials that may have already gone
into initiation
3. Reduce initiators
– metal contaminants
– water (copper tubing?, cast iron), salt, discolored meat
sources (likely rancid anyway)
– add chelators
– phosphates, citrates, etc.
– reduce light exposure for susceptible products
– i.e. cooked/dried product packaging
– vitamin E is effective as a feed supplement for
reducing rancidity in meat because it localizes in cell
wall membranes --- stabilizes phospholipids.
4. eliminate oxygen
– Vacuum processing and vacuum packaging
– avoid grinding, mixing to incorporate oxygen
– especially pork, poultry, deboned meat
– do not grind prior to freezing
– critical role for vacuum packaging
– oxygen permeability of film is a standard package
specification
– may be supplemented with aluminum foil and/or oxygen
absorber packs
5. Provide antioxidants
– compounds which will react with radicals to
terminate the cycle
– generally considered to be H donors
– ROO • + Anti - H
– R • + Anti - H


ROOH + Anti
RH + Anti
Note: slows rancidity but does not stop production
of aldehydes and ketones from hydroperoxides
Major antioxidants available for
meat applications
1. “Synthetic” antioxidants (phenolics)
– BHA - butylated hydroxy anisole
– BHT - butylated hydroxy toluene
– PG-propyl gallate
– TBHQ - tertiary butyl hydroquinone
–“primary” antioxidants
– differ in “initial” versus “long term”
effectiveness and for impact in specific foods
– consequently almost always used in
combinations
– permitted in dry sausage, fresh sausage, specific
cooked fresh meats, poultry products, rendered
fats
– permitted amounts are product dependent
Major antioxidants available for meat applications
2. Synergists - “Secondary”
– increase effectiveness of “primary” antioxidants
– citric acid/sodium citrate - chelators
– ascorbate/erythorbate, phosphates, lactates
Major antioxidants available for meat applications
3. “natural” antioxidants
– vitamin E/tocopherols
– generally not effective in meat as a added ingredient
– permitted in bacon to inhibit nitrosamines, some poultry,
rendered fats
– rosemary (spice)
– especially rosemary extracts
– other spices also have significant activity
– sage - pork sausage
Major antioxidants available for meat applications
4. Other significant antioxidants
– smoke
– phenols in wood smoke
Major antioxidants available for meat applications
4. Other significant antioxidants (continued)
– phosphates
– good chelators
– sodium nitrite
– very potent antioxidant
– synthetics are not permitted in cured meat except when dried
Review:
Essential fatty acids
– Linoleic (omega 6)
HOOC-C-C-C-C-C-C-C-C=C-C-C=C-C-C-C-C-C (omega)
1
2
3
4
5
6
7
8
9
10 11 12
13 14 15 16 17 18
– Linolenic (omega 3), double bonds at 9-10, 12-13, 15-16
-mammals can’t synthesize C9-C10 double bond fatty
acids
– Oleic (?) (omega 9), C=C at 9-10, limited synthesis by
mammals
Initiation sites of H extraction (a start of the
variation of end products produced by
oxidation)
– Primary site of attack is carbon adjacent to double bond
-for linoleic (18:2), carbon 11 is susceptible from
both sides (60X greater susceptibility than any
other fatty acid)
R-C=C-C-C=C-R
9
10
11
12
13
-produces primarily C9 and C13 hydroperoxy
radical in approximately equal proportions (51%, 49%, +
minute traces of C10 and C12) by subsequent reaction
with oxygen (R-OO·)
Sites of H extraction
– Differs for other unsaturated fatty acids
-oleic (18:1)
R-C-C=C-C-R
8
9
10
11
-attacked primarily at C8 and C11, forms
hydroperoxy radicals at C8, C9, C10, C11 in
similar (not equal) proportions (26%, 24%, 23%, 27%)
-linolenic (18:3) R-C-C=C-C-C=C-C-C=C-C-R
8
9
10 11
12
13
14
15
16
-attacked at C11 and C14, hydroperoxy
radicals formed at C9, C12, C13 and C16 in
very different proportions (33%, 10%, 12%, 45%)
Sites of H extraction
-Arachidonic (20:4)
R-C=C-C-C=C-C-C=C-C-C=C-R
5
6
7
8
9
10
11
12
13 14
15
-attacked at C7, C10, C13, hydroperoxy
radicals formed at C5, C8, C9, C11, C12,
C15 in very different proportions (27%,
7%, 9%, 11%, 6%, 40%)
Current focus is on finding fat substitutes
Consider protein, carbohydrate or “synthetic fat”
products
Another approach is fat “blockers” or absorbersalginate is one currently being studied