2B LIPIDS AND RELATED SYSTEMS: CHEMICAL REACTIONS OF TRIACYLGLYCEROLS

Fatty acids

• Most contain an even number of carbon atoms.

• Carbon chain length is up to 24 carbon atoms.

SATURATED

No double bonds are present in the carbon chain

SATURATED

Dietary effect is an increase in heart disease risk

Monounsaturated

One double bond is present in the carbon chain

Monounsaturated

Dietary effect is a decrease in heart disease risk

Polyunsaturated

Two or more double bonds are present in the carbon chain.

Polyunsaturated

Dietary effect is "mixed"; there have been several conflicting studies relative to heart disease risk.

Saturated

Monounsaturated

Polyunsaturated

Classification based on degree of unsaturation

Cis

Trans

Classification Based on Configuration of Double Bond

Cis

Naturally occurring fatty acids generally contain cis double bonds.

Trans

Hydrogenation converts trans dis double bonds to _ double bonds

Trans

fatty acids have effects on blood chemistry similar to those of saturated fatty acids

Omega-3

Omega-6

Classification Based on Location of Double Bond

Omega-3

First double bond is three carbons away from the CH, end of the carbon chain.

Omega-3

Linolenic acid (18:3) is the primary member of this family.

Omega-6

First double bond is six carbons away from the CH end of the carbon chain.

Omega-6

Linoleic acid (18:2) is the primary member of this family.

esters and alkenes

The chemical properties of triacylglycerols (fats and oils) are typical of _because these are the two functional groups present in triacylglycerols.

Hydrolysis

Saponification

Hydrogenation

Oxidation

Four important Triacylglycerols reactions

Hydrolysis

of a triacylglycerol is the reverse of the esterification reaction by which it was formed.

trimester of glycerols

three water molecules

glycerol

three fatty acids

Triacylglycerol hydrolysis

when carried out in a laboratory setting, requires the presence of an acid or a base

acidic conditions

the hydrolysis products are glycerol and fatty acids.

basic conditions

the hydrolysis products are glycerols and fatty acid salts.

digestion

Within the human body, triacylglycerol hydrolysis occurs during the process of

enzymes

Such hydrolysis requires the help of _ produced by the pancreas..

These _ cause the triacylglycerol to be hydrolyzed in a stepwise fashion.

monoacylglycerol

First, one of the outer fatty acids is removed, then the other outer one, leaving a

monoacylglycerol

most cases, this is the end product of the initial digestion (hydrolysis) of the triacylglycerol.

glycerol

enzymes remove all three fatty acids, leaving a free molecule of

enzymes

remove all three fatty acids, leaving a free molecule of glycerol

mono- and diacylglycerols

Naturally occurring _ are seldom encountermed

Synthetic mono- and diacylglycerols

are used as emulsifiers in many food products

Emulsifiers

prevent suspended particles in colloidal solutions from colloidal solutions from coaslescing and settling

Emulsifiers

are usually present in so-called fat-free cakes and other fat-free products.

complete hydrolysis

In situations where all three fatty acids are removed, the hydrolysis process is referred to as

complete hydrolysis of Triacylglycerols

produces glycerol and three fatty acid molecules

partial hydrolysis

If one or more of the fatty acid residues remains attached to the glycerol, the hydrolysis process is called

partial hydrolysis of Triacylglycerols

produced monoacylglycerol and two fatty acids

three water molecules

are required for the hydrolysis, one to interact with each of the ester linkages present in the triacylglycerol

glycerol and three fatty acids

breaking of the three ester linkages produces four product molecules

Saponification

is a reaction carried out in an alkaline (basic) solution.

glycerol and fatty acid salts

For fats and oils, the products of saponification are

First step: hydrolysis of the ester linkages to produce glycerol and three fatty acid molecules

Second step: involves a reaction between the fatty acid molecules and the base (usually NaOH) in the alkaline solution. This is an acid–base reaction that produces water plus salts:

The overall reaction of triacylglycerol saponification can be thought of as occurring in two steps

Saponification of animal fat

is the process by which soap was made in pioneer times.

Soap making

involved heating lard (fat) with lye (ashes of wood, an impure form of KOH).

lard

fat

lye

ashes of wood, an impure form of KOH

soap

Today most _ is prepared by hydrolyzing fats and oils (animal fat and coconut oil) under high pressure and high temperature.

Sodium carbonate

is used as the base

carboxylate ions

The cleansing action of soap is related to the structure of the _ present in the fatty acid salts of soap and the fact that these ions readily participate in micelle formation.

micelle formation

The cleansing action of soap is related to the structure of the carboxylate ions present in the fatty acid salts of soap and the fact that these ions readily participate in

micelle

is a spherical cluster of molecules in which the polar portions of the molecules are on the surface, and the nonpolar portions are located in the interior

surface

micelle polar portions of the molecules are on the

interior

micelle nonpolar portion of the molecules are located in the

Soaps

are carboxylic acid salts. They are thus ionic compounds, as are all salts.

Detergents

are also acid salts. They are, however, salts of sulfonic acids rather than carboxylic acids.

Sulfonic acids

were used as substitutes for carboxylic acids

general structures for a sulfonic acids and a carboxylic acid

1) small positive ion usually Na+ or K+

2) negative ion that connotations a very long carbon chain

Structurally, both soaps and detergents contain a very small positive ion (_) and a negative ion that contains a very long carbon chain.

“active ingredient”

– The negative ion is the _ in both soaps and detergents.

salt dissociation

In aqueous solution, _occurs, which releases the salt’s constituent ions.

Salt dissociation

This allows the carboxylate ions (soaps) and sulfonate ions (detergents) present to exert their effects.

“dual polarity”

The cleansing action of soaps and detergents relates to the_ that carboxylate and sulfonate ions possess.

tail

The long carbon chain present, which is called the _ of the ion, is nonpolar,

head

the small oxygen-containing group present, which is called the “_” of the ion, is polar.

nonpolar tail

long carbon chain

polar head

oxygen- containing group

Nonpolar substances

, such as fats, oils, and greases, are insoluble in water.

Soap or detergent

affects the solubility of such substances in water.

nonpolar “tail”

The _of the soap or detergent molecule interacts with (dissolves in) the insoluble nonpolar substance

polar “head”

of the soap or detergent molecule interacts with polar water molecules.

nonpolar -polar solubility

The soap or detergent thus overcomes the _ barrier

nonpolar portion of the carboxylate or sulfonate ion

dissolves in the nonpolar oil or grease

polar portion

maintains its solubility in the polar water.

formation of micelles

The penetration of the oil or grease by the nonpolar end of the carboxylate or sulfonate ion is followed by the

carboxyl sulfonyl groups (the micelle exterior) and water molecules

are attracted to each other, causing the solubilizing of the micelle.

carboxyl sulfonyl groups

the micelle exterior

micelles

do not combine into larger drops because their surfaces are all negatively charged, and like charges repel each other.

water-soluble micelles

are subsequently rinsed away, leaving a material devoid of oil and grease

Hydrogenation

is a chemical reaction that involves hydrogen addition across carbon–carbon multiple bonds, which increases the degree of saturation as some double bonds are converted to single bonds.

melting point

Hydrogenation

• With this change, there is a corresponding increase in the _of the substance

Hydrogenation

involving just one carbon–carbon bond within a fatty acid residue of a triacylglycerol

oleic acid 18:1

The structural equation for the complete hydrogenation of a triacylglycerol in which all three fatty acid residues are

partial hydrogenation

Many food products are produced via

partial hydrogenation

some, but not all, of the double bonds present are converted into single bonds.

partial hydrogenation

In this manner, liquids (usually plant oils) are converted into semi-solid materials.

partial hydrogenation

Peanut butter is produced from peanut oil through

partial hydrogenation

Solid cooking shortenings and stick margarine are produced from liquid plant oils through

partial hydrogenation

Soft-spread margarines are also _products.

refrigerator temperatures (48C)

Here, the extent of hydrogenation is carefully controlled to make the margarine soft at

Concern

has arisen about food products obtained from hydrogenation processes because the hydrogenation process itself converts some cis double bonds within fatty acid residues into trans double bonds, producing trans unsaturated fatty acids.

hydrogenation process

converts some cis double bonds within fatty acid residues into trans double bonds, producing trans unsaturated fatty acids

trans unsaturated fatty acids

hydrogenation process itself converts some cis double bonds within fatty acid residues into trans double bonds, producing

partially hydrogenated vegetable oils

play a role in raising blood cholesterol

(1) some of the cis double bonds present are converted to single bonds (the objective of the process) and

(2) some of the remaining cis double bonds are converted to trans double bonds (an unanticipated result of the process).

When the triacylglycerols in vegetable oils are subjected to partial hydrogenation, two types of changes, rather than just one, occur in the fatty acid residues present:

some of the cis double bonds present are converted to single bonds

the objective of the process

some of the remaining cis double bonds are converted to trans double bonds

an unticipated result of the process

cis–trans conversions

These latter_ affect the general shape of the fatty acid residues present in triacylglycerols, which in turn affects the biochemical behavior of the triacylglycerols

trans double bonds

Studies show that farty acids with_affect blood cholesterol levels in a manner similar to saturated fatty acids