Food BiotechnologyDr. Kamal E. M. Elkahlout

Food Biochemistry 2Lipids

Lipids: Fats & Oils

Characteristics of Lipids • Lipids are composed of C, H, O

– long hydrocarbon chain

• Do not form polymers– big molecules made of smaller subunits– not a continuing chain

fat

Fats store energy• Long HC chain

– polar or non-polar?– hydrophilic or hydrophobic?

• Function:– energy storage

• very rich• 2x carbohydrates

– cushion organs– insulates body

• think whale blubber!

Why do humanslike fatty foods?

ClassificationMany ways of classifying lipids:

Structural characteristics• Neutral fats – found in subcutaneous tissue and around organs

• Phospholipids – chief component of cell membranes

• Steroids – cholesterol, bile salts, vitamin D, sex hormones, and adrenal cortical hormones

• Fat-soluble vitamins – vitamins A, E, and K

• Eicosanoids – DHA (docosahexaenoic acid), EPA (eicosapentaenoic acid) (sources of omega 3,6 & 9)

• Waxes

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Fatty Acids

• Long-chain carboxylic acids• Insoluble in water• Typically 12-18 carbon atoms (even number)• Some contain double bonds

corn oil contains 86% unsaturated fatty acids and

14% saturated fatty acids

Fatty Acid Structure

• Carboxyl group (COOH) forms the acid.• “R” group is a hydrocarbon chain.

Fatty Acids

• The Length of the Carbon Chain– long-chain, medium-chain, short-chain

• The Degree of Unsaturation– saturated, unsaturated, monounsaturated,

polyunsaturated• The Location of Double Bonds

– omega-3 fatty acid, omega-6 fatty acid

The Length of the Carbon Chain

Short-chain Fatty Acid (less than 6 carbons)

Medium-chain Fatty Acid(6-10 carbons)

Long-chain Fatty Acid(12 or more carbons)

SaturatedFatty Acid

UnsaturatedFatty Acid

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Saturated and Unsaturated Fatty Acids

Saturated = C–C bondsUnsaturated = one or more C=C bonds

COOH

COOH

palmitoleic acid, an unsaturated fatty acid

palmitic acid, a saturated acid

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Properties of SaturatedFatty Acids

• Contain only single C–C bonds• Closely packed • Strong attractions between chains• High melting points• Solids at room temperature

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Properties of UnsaturatedFatty Acids

• Contain one or more double C=C bonds• Nonlinear chains do not allow molecules to

pack closely• Few interactions between chains• Low melting points• Liquids at room temperature

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Structures

Saturated fatty acids• Fit closely in regular pattern

Unsaturated fatty acids• Cis double bonds

COOHCOOHCOOH

C CH H

COOHcis double bond

Fatty Acids are Key Building Blocks

• Saturated Fatty Acid

• All single bonds between carbons

Monounsaturated Fatty Acid(MUFA)

One carbon-carbon double bond

Polyunsaturated Fatty Acid(PUFA)

More than one carbon-carbon double bond

Location of Double Bonds

• PUFA are identified by position of the double bond nearest the methyl end (CH3) of the carbon chain; this is described as a omega number;

• If PUFA has first double bond :– 3 carbons away from the methyl end=omega 3

FA– 6 carbons from methyl end=omega 6 FA

Omega-3

Omega-6

Degree of Unsaturation

• Firmness– saturated vs. unsaturated

• Stability– oxidation, antioxidants

• Hydrogenation– advantages, disadvantages

• Trans-Fatty Acids– from hydrogenation

Cis and Trans fats– isomerisation of cis to

trans occurs under extreme conditions of hydrogenation

– double bonds in fatty acids are almost always cis, which causes bends in the carbon chain.

– these bends do not allow the close packing and attractions of saturated fatty acids. Therefore, most unsaturated fatty acids are liquid at room temperature.

Cis-9-octadecenoic acid(Oleic acid)

Trans-9-octadecenoic acid(Elaidic acid)

Hydrogenation Process

• liquid hardens by hydrogenation (addition of hydrogen) – reduce the degree of

unsaturation

• briefly, oils are exposed to hydrogen gas at high tempt (2-10 atm, 160-220 0C) in the presence of 0.01-0.2% fine divided nicklel

Saturated vs. unsaturatedsaturated unsaturated

CLASSIFICATION OF FATTY ACIDS PRESENT AS GLYCERIDES IN FOOD FATS

 

I. Saturated Fatty Acids  

Butyric Butanoic CH3(CH2)2COOH butterfat

Caproic Hexanoic CH3(CH2)4COOH butterfat, coconut and palm nut oils

Caprylic Octanoic CH3(CH2)6COOH coconut and palm nut oils, butterfat

Capric Decanoic CH3(CH2)8COOH coconut and palm nut oils, butterfat

Lauric Dodecanoic CH3(CH2)10COOH coconut and palm nut oils, butterfat

Myristic Tetradecanoic CH3(CH2)12COOH coconut and Palm nut oil, most animal and plant fats

Palmitic Hexadecanoic CH3(CH2)14COOH practically all animal and plant fats

Stearic Octadecanoic CH3(CH2)16COOH animal fats and minor component of plant fats

Arachidic Eicosanoic CH3(CH2)18COOH peanut oil

Common Name

Systematic Name

Formula Common source

 Common Name

Systematic Name

Formula Common source

II. Unsaturated Fatty Acids  A. Monoethenoic Acids

 Oleic Cis 9-octadecenoic C17H33COOH plant and animal fats

Elaidic Trans 9-Octadecenoic C17H33COOH animal fats

B. Diethenoic AcidsLinoleic 9,12-Octadecadienoic C17H31COOH peanut, linseed, and

cottonseed oils C. Triethenoid Acids Linolenic 9,12,15-Octadecatrienoic C17H29COOH linseed and other seed

oilsEleostearic 9,11,13-Octadecatrienoic C17H29COOH peanut seed fats

D. Tetraethenoid Acids

Moroctic 4,8,12,15-Octadecatetraenoic C17H27COOH fish oils

Arachidonic 5,8,11,14-Eicosatetraenoic

C19H31COOH traces in animal fats

Common and Systematic Names of Fatty Acids 

Common Name

Systematic Name

Formula Common source 

A. Monoethenoic Acids 

Oleic Cis 9-octadecenoic C17H33COOH plant and animal fats

Elaidic Trans 9-Octadecenoic C17H33COOH animal fats

B. Diethenoic AcidsLinoleic 9,12-Octadecadienoic C17H31COOH peanut, linseed, and

cottonseed oils C. Triethenoid Acids Linolenic 9,12,15-Octadecatrienoic C17H29COOH linseed and other seed

oilsEleostearic 9,11,13-Octadecatrienoic C17H29COOH peanut seed fats

D. Tetraethenoid Acids

Moroctic 4,8,12,15-Octadecatetraenoic C17H27COOH fish oils

Arachidonic 5,8,11,14-Eicosatetraenoic

C19H31COOH traces in animal fats

C4 - 8  -

C6 - 4 970

C8 16 75

C10 31 6

C12 44 0.55

C14 54 0.18

C16 63 0.08

Fatty Acids M.P.(0C) mg/100 ml Soluble in H2O

C18 70 0.04

CHARACTERISTICS OF FATTY ACIDS

Effects of Double Bonds on the Melting Points

16:0 

6016:1 118:0 6318:1 1618:2 -518:3 -1120:0 75

F. A. M. P. (0C)

20:4 -50 

Lipid Formation

Glycerol Fatty Acid

GLYCERIDES

Monoglyceridea Diglyceride

H2C OH

HC OH

H2C OOC (CH 2)16CH3

H2C O

HC OH

H2C OOC (CH 2)16CH3

C (CH 2)16CH3

O

Triglyceride

H2C O

HC O

H2C OOC (CH2)1 6CH3

C (CH2)1 6CH3

O

OC (CH2)1 4CH3

( C1 8)

(C1 6)

(C1 8)

Triglycerides• Structure

– Glycerol + 3 fatty acids• Functions

– Energy source• 9 kcals per gram• Form of stored energy in adipose

tissue– Insulation and protection– Carrier of fat-soluble vitamins– Sensory properties in food

FAT AND OILS Mostly Triglycerides:

Triglycerides• Food sources

– fats and oils• butter, margarine, meat, baked goods, snack

foods, salad dressings, dairy products, nuts, seeds

– Sources of omega-3 fatty acids• Soybean, canola, walnut, flaxseed oils• Salmon, tuna, mackerel

– Sources of omega-6 fatty acids• Vegetable oils

MELTING POINTS OF TRIGLYCERIDES

C6 -15

C12 15

C14 33

C16 45

C18 55

C18:1 (cis) -32

Triglyceride Melting Point (°C)

C18:1 (trans) 15

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Learning Check

How would the melting point of stearic acid compare to the melting points of oleic acid and linoleic acid? Assign the melting points of –17°C, 13°C, and 69°C to the correct fatty acid. Explain.

stearic acid (18 C) saturatedoleic acid (18 C) one double bondlinoleic acid (18 C) two double bonds

Phospholipids• Structure

– Glycerol + 2 fatty acids + phosphate group

• Functions– Component of cell membranes– Lipid transport as part of lipoproteins– Emulsifiers– Phosphatidylcholine

• Food sources– Egg yolks, liver, soybeans, peanuts

Phospholipids• Hydrophobic or hydrophilic?

– fatty acid tails = hydrophobic– PO4 = hydrophilic head– dual “personality”

interaction with H2O is complex & very important!

It likes water & also pushes it away!

A Phospholipid

Steroids

• ex: cholesterol, sex hormones• 4 fused C rings

– different steroids created by attaching different functional groups to rings

cholesterol

Sterols: Cholesterol• Functions

– Component of cell membranes– Precursor to other substances

• Sterol hormones• Vitamin D• Bile acids

• Synthesis– Made mainly in the liver

• Food sources– Found only in animal foods

WAXES Fatty acids + Long chain alcohol

Important in fruits:

1. Natural protective layer in fruits, vegetables, etc.

2. Added in some cases for appearance and protection.

Beeswax (myricyl palmitate)

FAT SOLUBLE VITAMINS (A,D,E,K)

Vitamin A: CH2OH

CH3 CH3

CH3

CH3H3C

1234

5

678

9

Vitamin D2:

Vitamin E:

Deterioration of Fats

Rancidity • Is the chemical deterioration of fats• Are of two types

– Oxidative rancidity– Hydrolytic rancidity

Oxidative rancidity

• A hydrogen on the fatty acid molecule is displaced by energy(heat or light) to give free radical.

• Molecular oxygen can unite with the carbon that carries the free radical and form a peroxide.

• The energy from this activated peroxide can displace a hydrogen from another unsaturated fatty acid.

• The displaced hydrogen unites with the activated peroxide to form a hydroxide.

• The hydro-peroxide is very unstable and can decompose into compounds with shorter carbon chains. These include ketones, aldehydes and fatty acids that are volatile and contribute to off flavoures.

Oxidative Rancidity

Catalysts– Salt and trace metals– Bacteria and molds– Water– Light

Prevention• Addition of chelators• Use of antioxidants• Air tight storage.

Hydrolytic Rancidity

• Is the reaction between a triglyceride and 3 water molecule to give a glycerol and 3 free fatty acids.

Catalysts :• Heat• Fat splitting enzymes called lipases.

Prevention• Keep moisture level low• Inert gas packaging• sterilization

Functional Properties of Lipids

• Flavour• Basting – add crispiness to product• Add moisture to foods• Assist in browning• Frying • Aerating• Prevents products from sticking