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 |

HPlus…...

.…..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) 40 – 50%

palmitic (c16) 20 – 30%

stearic (c18) 10 – 15%

linoleic (c18:2) 2 – 25%

myristic (c14) 1 – 5%palmitoleic (c16:1) 3 – 6%

linolenic (c18:3) < 1%

arachidonic (c20:4) < 1%

Triglyceride: H O | || H C O C R1

| O H C O C R2

| O H C O C R3

| H

arachidonic

stearic*….oleic*…...linoleic.….linolenic....

myristic….palmitic*..palmitoleic

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

– small quantity (~ 1%) in meat lipids but important to rancidity because rancidity often begins with the phospholipids (located in cell membranes)

(phosphatidylcholine)

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 O H

| H C OH

| H C OH |

H

O

+ 3 K+ ¯O C R

fatty acid

– a large saponification number indicates short chain fatty acids

glycerol

Softness/melting pointb. 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 TBAthus 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

– fat tissue not a major source

– trans fatty acids (by-product of hydrogenated vegetable oils) H

C-C-C-C = C -C-C- H

– 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

– concerns for cholesterol (?)

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 • + H+

free radical

– 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 sequence2.) Propagation

– free radical reacts quickly and easily with oxygen to form hydroperoxy radical

– R • + O2 ROO • free radical 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 + R • hydroperoxide 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 = 125,000,000etc.

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 rancidity1. 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 ROOH + Anti

– R • + Anti - H 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 absorbers-alginate is one currently being studied