lipid powerpoint

General Information

• Definition– Substances found in living tissues which are

generally insoluble in water and are soluble in organic solvents (e.g. ether, chloroform, hexane)

– Exceptions• Some lipids (such as short chain fatty acids - < 4

carbons long) are water soluble• Others are only soluble in a limited range of

organic solvents

http://organicdivision.org/organic_solvents.html

General Information

• Use of fats and oils in body– Source of energy

• For all cells except erythrocytes and cells of central nervous system (which use carbohydrates for the most part)

– Carriers of fat-soluble vitamins (A, D, E, K)– Carrier of food flavors

• Most dietary lipids are triglycerides which are relatively tasteless on their own

http://www.ndsu.nodak.edu/instruct/tcolvill/435/erythrocytes.htm

General Information

– Help provide food texture that increases palatability (i.e. improves mouthfeel)

– Delays gastric emptying (which contributes to satiety)

– Adipose tissue insulates and cushions organs– Supplies essential fatty acids

http://en.wikipedia.org/wiki/Adipose_tissue

General Information

• Metabolic energy from lipids– calorie = the quantity of heat required to raise

the temperature of 1.0 g of water by 1 degree Celsius (°C)

– 1000 calories = 1 kilocalorie (abbreviated as kcal) = 1 Calorie (abbreviated as Cal)

– In general, lipids are 9 kcal/g (or 9 C/g)

Kcals – Lauric Acid

CH3(CH2)10COOH +17O2 12CO2 + 12 H2O


Bond Bond Energy (KJ/mol)

Number of bonds Total Bond Energy (KJ/mol)

C-C 347 11 3817

C=O 799 1 799

C-O 351 1 351

O-H 460 1 460

C-H 414 23 9522

O=O 499 17 8483

23432

CH3(CH2)10COOH +17O2 12CO2 + 12 H2O



Number of bonds

O-H 460 24

C=O 799 24

CH3(CH2)10COOH +17O2 12CO2 + 12 H2O



Number of bonds

Total Bond Energy (KJ/mol)

O-H 460 24 11040

C=O 799 24 19176

30216

30216 KJ/mol - 23432 KJ/mol = 6784 KJ/mol

MWlauric acid: 200.32 g/mol

CH3(CH2)10COOH +17O2 12CO2 + 12 H2O


6784 KJ/mol = 33.92 KJ/g

200.32 g/mol

33.92 KJ/g * 1 kcal = 8.11kcal/g

4.18 KJ

Nomenclature – fatty acids

• Nomenclature of fatty acids requires both a systematic approach and a knowledge of trivial names


• Systematic– Names of fatty acids are derived from the

appropriate parent hydrocarbon– Remove terminal “e” from parent and add suffix

“oic”– Example

• Hexane: CH3CH2CH2CH2CH2CH3

• Hexanoic acid: CH3(CH2)4COOH


– 2 main classes of fatty acids• Saturated: no double bonds• Unsaturated: double bonds present in carbon chain

– If 1 double bond, the parent alkene becomes “enoic acid”• Example

– 3-hexene: CH3CH2CH=CHCH2CH3

– 3-hexenoic acid: CH3CH2CH=CHCH2COOH

– If 2 double bonds, use the suffix “dienoic”• Similarly for:

– 3 double bonds, use “trienoic”– 4 double bonds, use “tetraenoic”– Etc.


• Trivial names– Names were selected prior to the identification of

the fatty acid’s chemical structure– Name often identified the source of the fatty acid– Examples:

• Saturated– C12: Lauric

– C14: Myristic

– C16: Palmitic

– C18: Strearic

– C20: Arachidic


– Examples:• Unsaturated

– C16:1: Palmitoleic

– C18:1: Oleic

– C18:2: Linoleic

– C18:3: Linolenic

– C20:4: Arachidonic


• Location of the double bond (several ways to show this)– Delta notation (δ or Δ): terminal COOH is #1

• Example– Oleic acid: CH3(CH2)7CH=CH(CH2)7COOH

» 9, 10-octadecenoic acid» Δ9-octadecenoic acid» 18:1Δ-9

– Linoleic acid:

CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH

» Δ9, 12-octadecadienoic acid» 18:2Δ-9,12


– Omega notation (ω or η): terminal CH3 is #1• Example

– Oleic acid: CH3(CH2)7CH=CH(CH2)7COOH

» ω9-octadecenoic acid» 18:1ω-9

– Linoleic acid:

CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH

» ω6, 9-octadecadienoic acid» 18:2-ω6, 9


• Most naturally occurring fatty acids have unconjugated double bonds– Double bonds are separated by one or more

single bonded C atoms– In most cases, double bonds are methylene

interrupted• CH2-CH=CH-CH2-CH=CH-

• Conjugated double bonds– Double bonds adjacent to one another

• CH2-CH=CH-CH=CH-

Methylene group

The Biochemical ω-system

• Animals cannot synthesize ω-3 or ω-6 fatty acids themselves– Animals lack the enzymes that catalyze

desaturation towards the methyl end• Enzymes in the body cannot function that close to the

methyl end• Can elongate and desaturate towards carboxyl end

– Plants and microorganisms can desaturate towards the methyl end

Since animals cannot make 18:2ω-3 or 18:ω-6 , they are termed Essential Fatty Acids (EFA)


• Using the omega notation can give necessary information in a brief way

– Example: What do we know from 18:2ω6?» 18 carbons» 2 double bonds» 1st double bond is 6 carbons down from the methyl end» Since we know that most double bonds are

methylene interrupted, the 2nd double bond is 9 carbons down from the methyl end

CH3(CH2)4CH=CH-CH2-CH=CH(CH2)7COOH


• What is the omega nomenclature of this fatty acid (please type into the chat space).


• What is the delta nomenclature of this fatty acid (please type into the chat space). Include all double bond locations.


• What is the common (i.e. trivial) name of this fatty acid (please type into the chat space).


• Cis versus trans– Most unsaturated fatty acids in nature will exist in

the cis configuration• If the fatty acid is in the trans configuration, it will be

stated

– The two configurations will yield different properties at room temperature

Oleic Acid: 18:1ω9

Elaidic Acid: 18:1ω9t

Liquid at Troom

Solid at Troom

EFA’s and deficiency

• Linoleic (18:2ω-6) deficiency– Clinical symptoms

• Scaly skin, water loss through skin, extreme thirst, poor wound healing, failure to gain weight, impaired reproduction, death

• Linolenic (18:3ω-3) deficiency– Noticed symptoms

• Blurred vision, neurological symptoms, tingling extremities

– Linolenic is critical to prostaglandin formation

http://www.ajcn.org/cgi/content/full/69/5/827

http://en.wikipedia.org/wiki/Prostaglandin

Omega 3 fatty acids

– 18:3ω-3 found in:• Soybean oil (~7%)• Canola oil (~10%)• Linseed oil (~50-60%)• Green leafy vegetables

• Desaturated 20:5ω-3 (EPA) in marine oils– Studied Eskimos in Greenland: found a decrease

in coronary heart disease compared to populations consuming less marine foods

VERY susceptible to oxidative rancidity = degradation

Omega 3 fatty acids

• Desaturated 20:5ω-3 (EPA) in marine oils– Studied Eskimos in Greenland: found a decrease

in coronary heart disease compared to populations consuming less marine foods

Other fatty acids of interest

• Vaccenic acid– 18:1Δ-11trans (18:1ω-7trans); also 18:1Δ11– Trans fatty acids that occur in milk and butterfat

due to biohydrogenation in rumen• Ricinoleic acid

– 12-OH octadeca cis-9-enoic acid– Oleic acid with an OH group on carbon 12 from

COOH end– Castor oil

• Laxative


• Erucic acid– 22:1ω-9 rapeseed and mustard oils– Accumulates in heart tissue when fed to rats– Genetic variant is canola oil, or low erucic acid

rapeseed (LEAR)• Branched chain

– Iso: mainly even C’s– Anteiso: mainly odd C’s– Occur in waxes like wool wax


• Milk fat group– Fats derived from milk of domesticated land

animals• Characteristic shorter chain fatty acids (C4 – C12) in

milk fat– Influences milk flavor and how milk is processed into dairy

products

• C4: butyric acid– A fatty acid that is liquid at Troom although saturated

– Normally masked in foods– If broken down via lipolysis, it will be very pungent

» Occurs due to extreme heat or agitation


• Lauric acid group– C12 is present

– Coconut oil• Vegetable butter group

– Cocoa butter• Oleic-linoleic acid group

– MAJOR GROUP– Vegetable oils– Saturated acids >20%


• Linolenic acid group– Contains 18:3– Soybean oil ~8% 18:3

• Animal fat group– 30-40% saturated– ~60% unsaturated– Lard, tallow

• Marine fat group– Highly unsaturated

Major Lipid Components – Acylglycerols• The majority of fatty acids are esterified to

glycerol, making them acylglycerols• Triacylglycerols are the most common in

foods– Mono- and diacylglycerols do exist as food

additives

Major Lipid Components – Acylglycerols• Review of ester formation

– Ester linkage forms between the carbon atom of carboxylic acid on the fatty acid chain and the oxygen atom of the alcohol on the glycerol backbone

R-C-OH + R’OH R-C-OR’ + H2O

O O

R : Fatty acid chainOC-OH : Carboxylic acid OH : Alcohol

http://en.wikipedia.org/wiki/Ester

Major Lipid Components – Acylglycerols

– Observe ester linkage

Glycerol

H

H-C-OH

H-C-OH

H-C-OH

H

+ 3 fatty acids

H O

H-C-O-C-R1

O

H-C-O-C-R2

O

H-C-O-C-R3

H

+ 3 H2O

Triacylglycerol = Triglyceride

1 mol of water is given off for every mol of “R” participating in the reaction

General Lipid Categories• Simple lipids (neutral lipids)

– Esters of fatty acids and alcohols; lipids derived from these by alkaline and acid hydrolysis (derived lipids)

– Includes fatty acids, glycerides, fatty alcohols– Examples

• Triacylglycerols (i.e. triglycerides)– Esters of fatty acids and glycerol

• Waxes– Esters of fatty acids with alcohols other than glycerol– Normally: long chain alcohols (e.g. C24)

– Water insoluble

General Lipid Categories

• Compound (complex) lipids– Lipids containing other groups in addition to

an alcohol-fatty acid ester linkage– Phospholipids

• Phosphoglycerides or glycerophospholipids• Glycerol + fatty acids + phosphate + another group• Example: phosphatidic acid (major component of

cell membranes)


• Example: cardiolipin (a phosphatidyl glycerol)– An important component of the inner mitochondrial

membrane– Important to the electron transport chain that produces ATP


• Example: Phosphatidyl-Choline (component of lecithin) Ethanolamine (membrane lipid)

Serine (for NS cell functioning) Inositol (substrate for cell signaling

enzymes)


– Sphingolipids• Associated with plant and animal membrane

components• Play an important role in both signal transmission

and cell recognition • Sphingosine + derived lipids + water soluble

products– No glycerol backbone


• Examples– Sphingomyelin

– Cerebrosides


– Sterols, other lipids and essential oils• All contain the cyclopentanoperhydrophenanthrene

ring system

http://journals.iucr.org/a/issues/2006/02/00/xo5005/xo5005fig1.html


– Sterols, other lipids and essential oils• Cholesterol: typical in animals

– Plants do have detectable levels, but VERY low– Has the ability to undergo oxidation, leading to heart

disease and cancer» Low density lipoprotein oxidation can lead to plaque


• Phytosterols: plant sterols– Example: stigmasterol (in soybeans)– May reduce the risk of CHD by lowering blood cholesterol lev

els

http://ific.org/publications/factsheets/sterolfs.cfm

http://ific.org/publications/factsheets/sterolfs.cfm


• Essential oils– Not “oils” in the real sense

• Actually terpenes ((C5H8)n hydrocarbons)

– Often mixed with other lipids in waxy coats or located in special oil sacs in the skin of citrus fruits

– Important to citrus-based flavor development

http://en.wikipedia.org/wiki/Terpene

Natural fat and oil composition

• Fats of aquatic origin– Number of carbons usually exceeds 20

• Mainly C14 – C24

– Major saturated acid is palmitic (16:0): 15-20% by wt.

– Monoenoic acids are 16:1, 18:1, and 20:1• Usually with double bond position at 9, but some have

double bond at carbon 1

– Many C16, C18, C20, and C22 polyenoic acids• ω3 family: 18:3, 18:4, 20:4, 20:5, 22:5, and 22:6


– Other lipids present• Glycerol ethers• Waxes

– Occur occasionally as an oil of the sperm whale– Ester of long chain alcohol and a fatty acid


• Milk fats– Cow’s milk fat

• High in C4 – C10 fatty acids: 20 – 30% on a molar basis

– Human milk fat• Much lower in C4 – C10, but higher in C12 – C14


• Vegetable fats (usually oils)– Present in all parts of plants but usually highest

in fleshy part of fruit or in seeds (seed oils)– Oils and fats from different parts of plant differ in

composition


• Example: Erucic acid (22:1Δ13) in rapeseed plant– No erucic acid in leaves– In rapeseed oil, there’s approximately 40 – 50% erucic acid– Problem

» Erucic acid accumulates in heart muscle, not in adipose tissue, upon feeding

» Heart lacks enzyme for oxidizing erucic acid» Could be a problem if an excess of one fatty acid

accumulates in heart muscle membranes» The problem was avoided with the development of low

erucic acid rapeseed oil (LEAR)


• Example: castor plant– Ricinoleic acid (12-OH 18:1)– Leaves: no ricinoleic acid– Castor oil: ~90 ricnioleic acid


• Depot fats of land animals– Adipose tissue fat

• Fats are laid down in adipose tissue as triglycerides• Two sources of fatty acids

– Endogenous supply from CHO and protein synthesis– Dietary fat (this may be modified by the animal)

• Easy to distinguish from fish oils as they are solid or semi-solid at Troom


• Characteristics– Almost entirely C16 (32%) and C18 (62%) fatty acids

– C16 is almost all 16:0

– C18 is almost all 18:1

– Stearic-rich (18:0) fats come from ruminants such as sheep, cattle, and deer

» Hydrogenation of fatty acids by rumen bacteria» Also due to hydrogenation in rumen, small amounts of

trans fatty acids» The fatty acid composition of adipose tissue can be

changed drastically by changing animal’s diet – pig feed high in 18:2 (corn) can result in “soft-pork” problem (i.e. soft adipose tissue = runny fat)


• Summary– Animals do not generally produce linoleic and

linolenic acids (EFA), thus they must acquire it from their diet

– Plants produce linoleic and linolenic, but carry out less conversion to the longer, more unsaturated fatty acids

– Microorganisms are versatile• They can produce all kinds of fatty acids including

branched chain, hydroxyl, keto, and cyclic fatty acids

Lipid properties

Property Oil Water

Molecular weight 885 18

Melting point (ºC) 5 0

Density (kg/m3) 910 998

Viscosity (mPa*s) ~50 1.002

Specific heat (J/kg*K) 1980 4182

Refractive index 1.46 1.33

Table 1. Physicochemical property comparison – Triolein oil vs. water

Lipid properties

• Refractive index (RI)– Used to determine what the fatty acid

composition might be– A ratio of the velocity of light in air to the velocity

of light in the substance– A function of the temperature and wavelength of

light employed

http://en.wikipedia.org/wiki/Refractive_index

Lipid properties

– Extent of refraction depends on intermolecular attractions• Refraction

Lipid properties

– Bending of light as it passes from one medium to another– The density of the medium impacts the speed of light through

the medium» This causes the light to bend at different angles

– Extent of refraction is also impacted by intermolecular attractions

– RI increases with increasing chain length and with increasing unsaturation (i.e. number of double bonds)

– Use in industry» As a control procedure during hydrogenation (a change

in RI results when the number of double bonds changes)

Lipid properties

• Iodine value– The number of grams of iodine absorbed by 100

grams of fat– Measure of the degree of UNsaturation– Halogens (e.g. Cl, Br, I) react with double bonds

in fatty acids under mild conditions

http://www.chemsoc.org/viselements/Pages/data/intro_groupvii_data.html

Lipid properties

– The reaction results in addition to the double bond

H H H H

- C = C - - C - C -

I I

I2

Lipid properties

Calculation of Iodine Value – Oleic Acid

CH3(CH2)7CH=CH(CH2)7COOH

1 mol of I2 adds across each double bond – therefore, in the case of oleic acid, 1 mol of I2 will add across the 1 double bond in oleic acid

Calculation of Iodine Value: Oleic Acid (18:1Δ-9)


For each mol of lipid, 1 mol of I2 will add across each double bond. Therefore in the case of oleic acid, with one double bond, 1 mol of I2 will add to 1 mol of oleic acid.

Since we know the molecular weights of both oleic acid (282g/mol) and I2

(254g/mol) we can establish a mass ratio on a per mol basis that we can use to calculate how many grams of I2 will add across 100g of oleic acid.

In other words, if 1 mol of I2 adds to 1 mol of oleic acid, then 254g of I2 add to 282 g of oleic acid. Thus, we can determine how many grams of I2 add to 100g of oleic using the following ratio:







254gI2 XgI2

282gOleic Acid 100gOleic Acid

=







254gI2 XgI2


(254gI2)(100gOleic Acid) = (XgI2

)(282gOleic Acid)

X = 90gI2

=







254gI2 XgI2



)(282gOleic Acid)

X = 90gI2

meaning that 90g of I2 will add to 100g of oleic acid

=

Calculation of Iodine Value: Linoleic Acid (18:2Δ-9, 12)


For each mol of lipid, 1 mol of I2 will add across each double bond. Therefore in the case of linoleic acid, with two double bonds, 2 moles of I2 will add to 1 mol of linoleic acid.

The MW of linoleic acid is 280g/mol and the MW of I2 is 254g/mol. We can establish the mass ratio to calculate how many grams of I2 will add across 100g of linoleic acid. Remember that 2 moles of I2 add to 1 mol of linoleic acid, so (254g/mol * 2 moles) of I2 add to (282 g/mol * 1 mol) of linoleic acid.





508gI2 XgI2

280gLinoleic Acid 100gLinoleic Acid

=





508gI2 XgI2



)(280gOleic Acid)

X = 181gI2

=





508gI2 XgI2



)(280gOleic Acid)

X = 181gI2

meaning that 181g of I2 will add to 100g of linoleic acid

=

Lipid properties

• Saponification value– Number of mg of potassium hydroxide required

to saponify with 1 gram of fat or oil– 3 moles of KOH react with on mol of

triacylglycerol

http://mw1.merriam-webster.com/dictionary/saponify

Lipid properties

– If the triglyceride contains low molecular weight fatty acids, the number of molecules present in a 1 gram sample of the fat will be greater than if the fatty acids have long carbon chains and high molecular weights• The fat with the lower molecular weight fatty acids will

consequently have a higher saponification value• Butter, for example, with a high percentage of butyric

acid, has a high saponification value

Lipid properties

Fat or oil Saponification # Iodine #Beef tallow 194 – 200 34 – 43

Cocoa butter 192 – 198 32 – 42

Coconut oil 245 – 262 6 – 10

Cottonseed oil 192 – 196 103 – 112

Lard 193 – 200 50 – 80

Milk fat 210 – 233 26 – 35

Peanut oil 186 – 194 89 – 98

Table 1. Examples saponification and iodine numbers

Modification of fats and oils

• Fats have the ability to enhance the palatability of foods

• Because of this there is a great emphasis on the crystallization and melting behavior of fats

• Unique fatty acid distribution of some natural fats makes them undesirable for certain applications


– Physical characteristics are influenced by:• Carbon chain length

– Increased chain length = increased melting point

• Degree of unsaturation– The more unsaturated a fatty acid is, the more liquid it will be

at Troom

• Distribution of fatty acids on glycerolmonoglyceride diglyceride triglyceride


• Modified in order to change the solid fat content (SFC) of lipids– The fraction or percentage of a lipid that is solid

at a given temperature– Enables less expensive lipids to be used– Can reduce unsaturation, reducing susceptibility

to oxidation– Can also increase unsaturation, potentially

increasing nutritional quality


• Common processes for modifying lipids– Blending– Dietary interventions– Genetic manipulation– Fractionation– Interesterification– Hydrogenation


• Interesterification– Process used to improve the consistency of

some natural fats to enhance their usefulness– Alteration of the original fatty acid distribution on

the glycerol backbone• Affects melting and crystallization properties• Rearrangement at random


– Process• Rearrangement of fatty acids so that they become

distributed RANDOMLY among the TAG molecules• Mixing of 2 esters resulting in the exchange of “R”

groups

O O

R1C – O – CH3 + R2C – O – C2H5

O O

R1C – O – C2H5 + R2C – O – CH3


• Occurs within TAG’s or between TAG’s• Heat fat at high temperatures• Use a catalyst to speed up the reaction

– Most popular: NaOCH3 (sodium methoxide)

– Alteration of physical properties of fats and oils• Example: cocoa butter (mp 28 – 30ºC)

– Cocoa butter has a characteristic fatty acid composition and distribution

» “Melts in your mouth, not in your hands”– Once cocoa butter undergoes radomization by

interesterification, it no longer melts at the same temperature


Lipid MP (ºF) – Before MP (ºF) – After

Soybean oil 19.4 41.9

Cottonseed oil 50.9 93.2

Coconut oil 78.8 82.8

Palm oil 103.7 116.6

Lard 109.5 109.5

Tallow 115.2 112.3

40% hydrog. cottonseed oil 136.0 106.0

23% hydrog. palm oil 122.3 104.5

Table 2. MP changes due to interesterification


• Hydrogenation– Very important to the oil industry

• Need to modify natural liquid oils to make fats with a wide range of properties

– Soft and greasy to hard and brittle

• Usually only partial hydrogenation occurs


– Simple reaction

H H

- C = C - + H2 - C - C - H H H H

• Addition of H2 across double bonds makes compounds saturated

• Alters:– Molecular configuration– Number, geometry and location of double bonds

Most importantly, it can result in the formation of trans fatty acids!!!


– Reasons for hydrogenation• Convert liquid fats into plastic fats (suitable for

manufacture of shortenings and margarine)• Improve resistance of fats and oils to deterioration

through oxidation or flavor reversion• Convert soft fats into firmer fats• Improve color


– General mechanism for hydrogenation• Requires a catalyst

– Technically, it will happen naturally, however, the reaction will take place VERY slowly

– Usually nickel– Heterogeneous

» In other words, the catalyst is in a different chemical state (typically solid when hydrogenating a liquid oil)

Modification of fats and oils• Mechanism

CH2-CH=CH-CH2-

CH2-CH-CH-CH2-

Ni Ni

Absorption of fatty acid onto catalyst

Double bond is broken and 2C-Ni bonds form

Reaction with absorbed H goes to partially hydrogenated states

CH2-CH2-CH-CH2-

Ni

CH2-CH-CH2 -CH2-

Ni+

These may then go either of two ways

CH2-CH2-CH2-CH2-

H desorption from catalyst

Fully hydrogenated

Loses H from a C atom adjacent to a C-Ni bond

CH2-CH=CH-CH2-

CH=CH-CH2-CH2-

CH2-CH2-CH=CH- Double bond will be cis or trans

These fatty acids can go back into the cycle


– Rate of reaction depends on:• Nature of substance being hydrogenated

– The greater the number of double bonds, the faster the reaction

• Nature and concentration of the catalyst• Concentration of H2

• Temperature, pressure and degree of agitation– Increasing the temperature, pressure of H2 and degree of

agitation will all speed up the reaction


– If unlimited H2 at catalyst surface:• Hydrogenation will be non-selective

– Selectivity: the tendency for more unsaturated fatty acids to be reduced before those fatty acids that are more saturated

» Example: 18:3 are hydrogenated before 18:2 which are hydrogenated before 18:1

• Any factor influencing the amount of H2 at the catalyst surface will influence the rate and selectivity

• Control of selectivity– Increase selectivity by reducing H2 at the catalyst surface

» Increase T, decrease P, increase amount of catalyst


– Partial hydrogenation (e.g. in soybean or vegetable oil)• In practice, partial hydrogenation is carried out in

vessels known as “converters”• Closed, pressurized vessels with a capacity of

~60,000 pounds• Agitation, heating, cooling and H2 inlet/vent systems

• Temperature ~ 175ºC• Typical catalyst is Ni (0.01 – 0.02% of oil)• H2 at 5 – 50 psi

• After partial hydrogenation, the oil is cooled, drained and the catalyst is removed by filtration

http://www.kokuragousei.co.jp/newpage52e.htm

http://en.wikipedia.org/wiki/Pressure


– Testing partially hydrogenated oils• Samples are analyzed for

– Iodine value– Refractive index (AOCS method)– Melting point– Infrared spectroscopy (IR)

Polling question - hydrogenation

Which fatty acid would hydrogenate faster: one with an IV of 103 or one with an IV of 80?

Deterioration reactions

• Autoxidation– General description

• Atmospheric oxidation of fats and oils

– General reaction characteristics• Autocatalytic• Has an induction point• Accelerated by metals, light, and temperature• Surface dependent• Unsaturation dependent• Produces a variety of oxidation products

Polling question - Autoxidation

Which of the following fatty acids is the most susceptible to autoxidation:

A. Arachidic

B. Arachidonic

C. Palmitoleic

D. Myristic


– Mechanism of lipid oxidation• Free radical chain mechanism• Initiation

RH R· + H·

– Removal of a H atom from a C adjacent to a double bond– H atom is usually from the methylene group– Example:

R-CH=CH-CH2-R’ R-CH=CH-C·H-R’

Alkyl radical

Methylene group


• Propagation– Alkyl radical (i.e. fatty acid free radical) combines with O2 to

first form peroxy radical

R· + O2 ROO·

– Peroxy radical then combines with fatty acid to form hydroperoxide and another alkyl radical

ROO· + RH ROOH + R·

Peroxy radical: initial product during propagation

Hydroperoxide


• Termination– Reaction of 2 radicals, resulting in a non-propagating product

R· + R· RR

ROO· + ROO· ROOR + O2

RO· + R· ROR

ROO· + R· ROOR

2RO· + 2ROO· 2ROOR + O2


– Primary product = hydroperoxide (peroxide)• Measurement: peroxide value

– Problem: hydroperoxide decomposition» Example: break down product = hexanal

» When measuring PV, the value rapidly increases after lag period, but then decreases as hydoperoxide decomposes

Co

nce

ntr

atio

n

Time

Hexanal


– Induction period (i.e. lag period)• No visible signs of oxidation occurring

– Doesn’t mean that oxidation isn’t occurring, though

• During the initiation phase– Symbolizes reactants coming together


– Antioxidants• Function to interrupt the free-radical mechanism

– Extends the induction period– Delays the onset of oxidative rancidity

• Limit on the amount of an antioxidant that can be used– 0.02% of the weight of the fat

• Must be added at the beginning of a process to be most effective


– Initiation reaction• Subject of great interest

– Common investigations: site of attack, energy requirements

• H atom adjacent to double bond is most susceptible– Easy to remove because of neighboring double bond

• Unsure where 1st radical comes from in foods– Perhaps singlet oxygen– Trace metals may initiate the reaction (e.g. Cu, Fe)


– Oxidation of monoenoic acids• C8 and C11 are most likely sites for hydrogen removal

• They then react with O2 and attack another RH resulting in hydroperoxide formation

• Hydroperoxide decomposes to aldehydes, alcohols and ketones

• 4 free radicals/4 hydroperoxides– Decompose

» Aldehyde production common» Trace metals, temperature and light accelerate

hydroperoxide decomposition

http://class.fst.ohio-state.edu/FST605/lectures/lect4.html

Deterioration reactionsOxidation of linoleic acid

-CH=CH-CH2-CH=CH-

-CH=CH-CH-CH=CH-

-CH-CH=CH-CH=CH- -CH=CH-CH=CH-CH-

-CH-CH=CH-CH=CH- -CH=CH-CH=CH-CH-

C-CH=CH-CH=CH-(CH2)4-CH3 C-CH2-CH2-CH2-CH2-CH3

H H

9 13121110

9 13121110

Loss of proton

9 13121110

9 131211109 13121110

9 131211109 13121110

13 17161514 18

Double bond shift for isomerization

O2, RH O2, RH

OOH OOHDecomposition of hydroperoxide

Decomposition of hydroperoxide

Hexanal2, 4-decadienal

O O


– Aldehydes produced from various unsaturated fatty acids• Oleic acid

Hydroperoxide Aldehyde formed

C8 2-undecenal

C9 2-decenal

C10 n-nonanol

C11 n-octanol


• Linoleic acid


C9 2, 4-decadienal

C11 2-octenal

C13 n-hexanal


• Linolenic


C9 2, 4, 7-decatrienal

C11 2, 5-octadienal

C12 2, 4-heptadienal

C13 3-hexenal

C14 2-pentenal

C16 propanol


– Nutritional implications of autoxidation• Loss of β-carotene (provitamin A)• Loss of fat-soluble vitamins (A, D, E, K)• Loss of essential fatty acids• Possible build up of polymeric material• Loss of protein quality

– Free radicals will react with protein– Carbonyl-amine reactions (i.e. Maillard browning reaction)

– Other implications• Loss of color and flavor = shelf life limitations• Warmed over flavors in refrigerated foods

Other deteriorative reactions• Lipoxygenase reactions

– Enzyme catalyzed lipid oxidation– Not the same mechanism as autoxidation– Common reaction in soybeans

Other deteriorative reactions• Lipolysis

– Hydrolysis reaction• Water is involved• Ester linkages can be broken by re-addition of water

produced when ester linkage is created

– Can occur due to enzymes, thermal stresses (e.g. heat, moisture)

– Known as:• Lipolysis, lipolytic rancidity, hydrolysis, hydrolytic

rancidity

DO NOT CONFUSE WITH OXIDATIVE RANCIDITY!!!

Other deteriorative reactions• Lipolysis in heated fats – deep fat frying

– Usually at temperatures > 180ºC– Results when oil is reused– Moisture from food can cause hydrolysis (i.e.

lipolysis)– Causes color changes (i.e. darkening) , an

increase in viscosity, a decrease in smoke point, and potentially toxic products

Other deteriorative reactions– Glycerol dehydration to acrolein (acrylaldehyde)

• Moisture from food escapes and causes oil to hydrolyze into glycerol and free fatty acid(s)

• Responsible for puffs of smoke– Very pungent – choking irritating odor

• Results in smoke point depression

H

H-C-OH

H-C-OH

H-C-OH

H

GlycerolH O C

C-H

C-H

H

Acrolein

Heat

-H2O

Other deteriorative reactions• Thermal polymerization

– When a fat/oil is heated to a high temperature (> 250ºC) in the absence of oxygen

– Also occurs during deep fat frying

http://www.uvi.edu/Physics/SCI3xxWeb/Structure/Polymerization.html

Other deteriorative reactions– Diels-Alder reaction

• A conjugate addition reaction of a conjugated diene to an alkene (the dienophile) to produce a cyclohexene

http://www.chem.ucalgary.ca/courses/351/Carey/Ch10/ch10-5.html

Conjugateddiene

Dienophile Cyclicadduct

H O C

C-H

C-H

H

Acrolein

CH2

HC

HC

CH2

+

1, 3-butadiene

CHO

1, 2, 3, 6 –tetrahydro benzaldehyde

+

• Can cause color and viscosity changes

• Also, can be

carcinogenic

Antioxidants

• General definition– Substances that slow or prevent oxidative

reactions that would result in undesirable changes• Examples: the development of off-flavors,

discoloration, and loss of nutritive value

– Antioxidants– Synergists– Oxygen displacers (e.g. inert gases)– Protective coatings

Antioxidants

• Better definition– Compound which prevents rapid oxidation of

food products by extending or prolonging the induction period

Antioxidants

• Protection factor– Ratio:

induction period protected

induction period unprotected

Antioxidants

• Mechanism of antioxidant action– Type I

• Primary antioxidants• “Free radical chain stoppers”

– Interacts with free radicals produced during the initiation phase (e.g. R· or ROO·)

• Normally phenolic (e.g. BHA, BHT)

OH H atom interacts with R· or ROO· to form RH or ROOH

Antioxidants

– Type II• Inhibitors of free radical production in foods• Examples: EDTA, citric acid, phosphates, and

phosphoric acid– Tie up metal catalysts

Antioxidants

– Type III• Elimination of environmental factors• Examples:

– Lowering oxygen partial pressure in a package» Vacuum, inert gas, airtight containers

– Lowering temperatures» -12 to 20ºC

– Exclusion of light– Prevention of contamination by catalytic, prooxidative metals

Antioxidants

• Example mechanismsR· + AH RH + A·

RO· + AH ROH + A·

ROO· + AH ROOH + A·

R· + A· RA

RO· + A· ROA

Antioxidants

• Competition between inhibitory reaction

ROO· + AH ROOH + A·

and the chain propagating reaction

ROO· + RH ROOH + R·

Antioxidants• Structures of synthetic antioxidants

OCH3

anisole

OCH3

OH

hydroxyanisole

CH3

toluene

CH3

OH

hydroxytoluene

Antioxidants• Major antioxidants used in foods

2 and 3-tert-butyl-4-hydroxyanisole butylated hydroxytoluene

propyl gallate

Antioxidants• Growing interest in natural antioxidants

– Examples• Tocopherols

– Principal antioxidant in vegetable oils» Most widely distributed antioxidants in nature

– Example: vitamin E

Antioxidants• Ascorbic acid (i.e. vitamin C)

– Works synergistically with vitamin E by regenerating it

Antioxidants• Chelating agents

– Tie up metals– Examples:

EDTACitric acid

Antioxidants• Plant extracts

– Rosemary» Fresh» Not as effective as vitamin E, BHA, etc

– Soybean– Honey

Antioxidants• Popular misconceptions of antioxidants

– Improve flavor of poor quality fats and oils– Improve oil in which oxidative ancidity has

developed– Prevent microbial decay– Prevent hydrolytic rancidity

ReferencesGunstone F. 1999. Fatty Acid and Lipid Chemistry.

Gaithersburg: Aspen Publishers, Inc.

McClements DJ and Decker EA. 2007. Lipids. In: Fennema's Food Chemistry (4th Edition). Damodaran S, Parkin KL, Fennema OR eds. Boca Raton: CRC Press. P 155-212.

Nawar WW. 1996. Lipids. In: Food Chemistry (3rd edition) Fennema OR, editor. New York: Marcel Dekker, Inc. p 225-320.

http://www.amazon.com/exec/obidos/search-handle-url/ref=ntt_athr_dp_sr_1?_encoding=UTF8&sort=relevancerank&search-type=ss&index=books&field-author=Srinivasan%20Damodaran

lipid powerpoint

Documents

unsaturated fatty acids

nomenclature fatty acids

fatty acid examples

ofthis fatty acid

short chain fatty acids

essential fatty acids

main classes of fatty

double bonds unsaturated