HmEc- Lipids

Elemental composition of lipids

Carbon, hydrogen, oxygen

Chemical structure of lipids

triglycerides CH3(CH2)nCOOH

Triglyceride composition

one glycerol molecule with three fatty acid molecules

What is this?

Triglyceride moelcule

What is this?

Fatty acid moleule

How is a triglyceride made?

When a glycerol molecule joins three fatty acids, resulting in the loss of three water molecules

Classification of lipids

Saturated fatty acids, mono-unsaturated fatty acids, poly-unsaturated fatty acids

Carbon quota saturated fatty acids

each carbons has full quota of hydrogen atoms

Carbon bonding in saturated fatty acids

no double bonds between carbon atoms

Saturated fatty acids state at room temperature

solid

Carbon quota mono-unsaturated fatty acids

not all carbons saturated with hydrogen

Mono-unsaturated fatty acids state at room temperature

soft

Carbon bonding of mono-unsaturated fatty acids

one double bonds between carbon atoms

Carbon quota poly-unsaturated fatty acids

not all carbons saturated with hydrogen

Carbon bonding of poly-unsaturated fatty acids

more than one double bond between carbons

Poly-unsaturated fatty acids state at room temperature

soft/liquid

Sources of saturated fatty acids

animal

Sources of mono-unsaturated fatty acids

plant/fish

Sources of poly-unsaturated fatty acids

plant/fish

melting point of saturated fatty acids

high

melting point of monosaturated fatty acids

low

melting point of polyunsaturated fatty acids

lowest of all acids

example of saturated fatty acid

butyric acid in butter

example of mono-unsaturated fatty acid

oleic acid in olive oil

example of poly-unsaturated acid

linoleic acid in nuts

Distributions of types of fats in butter

52% saturated, 21% mono-unsaturated, 3% polyunsaturated

Distribution of types of fats in olive oil

14% saturated, 73% mono-unsaturated, 8% polyunsaturated

Distributions of types of fats in block margarine

26% saturated, 34% mono-unsaturated, 12% polyunsaturated

Sources of essential fatty acids

nuts, seeds, olive oil, oily fish

Biological functions of essential fatty acids

aids cell membrane formation, reduced CHD by raising high density lipoprotein

What does high density lipoprotein do?

removed cholesterol from the blood and lowers low density lipoprotein

Examples of essential fatty acids

Linoleic, linolenic and arachidonic acids

Sources of omega-3 acids

oily fish

Functions of omega-3 acid

lower blood fat levels and aids foetal brain development

Two types of omega-3 acids

Eicosapentaenoic and docosahexaenoic

Chemical structure of omega-3 acids

double bond between third and fourth carbons

Cis-fatty acids

mono and polyunsaturated fats when hydrogen atoms on either side of double bond are both above or below hydrocarbon chain

Trans-fatty acids

mono and polyunsaturated fats when the hydrogens either side of the double bond are on opposite sides of hydrocarbon chain

Source of cis-fatty acids

sunflower oil

Source of trans-fatty acids

margarine

Properties of lipids

Solubility, Absorption, Heating, Emulsions, Emulsifiers, Hydrogen, Rancidity, Plasticity

Solubility of lipids

insoluble in water but soluble in solvents such as ether and benzene

Plasticity of lipids

solid, liquid or spreadable, determined by degree of unsaturation: fewer unsaturated fatty acids=more solid

Hydrogenation of lipids

hydrogen pumped through liquid unsaturated fat, converts to solid saturated fat, double bonds split and absorb hydrogen

What is hydrogenation used to make

margarine

Lipids absorption of flavours

readily absorb flavours, keep covered

Melting point of fat

30-40 degrees

Smoke point of oil

250 degrees

smoke point of fat

200 degrees

What happens if lipids are overheated

glycerol seperates from fatty acids and turns to acrolein, makes blue haze or smoke and smells

What is a flash point

when extreme overheating causes vapour to spontaneously ignite

Flash point for oils

325 degrees

Flash point for fats

310 degrees

What is an emulsion

colloidal solution with two immiscible solutions forced to mix together

types of emulsions

temporary or permanent

Emulsifier definition

molecule with hydrophillic head and hydrophobic tail

How does an emulsifier form a permanent emulsion

head attaches to water and tail attaches to oil, eg lecithin in mayonnaise

Stabiliser defintion

long chained molecules used to maintain emulsion and separate oil droplets to prevent coalescing, eg gums in yoghurt

Rancidity definition

the spoilage of foods

Two types of rancidity

oxidative and hydrolytic

How does oxidative rancidity occur?

oxygen combines with carbon atom in double bond, bad smell, aided by light

How does hydrolytic rancidity occur?

enzymes and bacteria hydrolyse lipids and change them to fatty acid and glycerol, bad smell and taste, can happen in freezer

How to prevent rancidity

store in cool, dark place, wrap well, add antioxidants in production

Function of antioxidants

prevent oxidative rancidity by attaching to oxygen so its unable to bond

antioxidative vitamins

A,C,E

What does antioxidant BHT stand for

Butylated Hydroxytoluene

What does antioxidant BHA stand for?

Butylated Hydroxyanisole

Biological function of lipids

• heat and energy

• excess stored as adipose

• protect vital organs

• provide fat-soluble vitamins

• provide essential fatty acids

• delay hunger

• help lower cholesterol

RDA of lipids

max 70g/day, max 30g saturated fat for men and 20g saturated fat for women

Energy value of lipids

1g=9kcal/37kj

Associated dietary disorders of lipids

obesity, CHD, high cholesterol, strokes

Digestion of lipids in mouth

food chewed into smaller pieces

Digestion of lipids in stomach

heat melts fat

Digestion of lipids in liver

bile in duodenum emulsifies large fat molecules into smaller ones

Digestion of fat in the pancreas

pancreatic juice in duodenum contains lipase to break lipids into fatty acid and glycerol

Digestion in small intestine

ileum secretes lipase

Absorption of lipids

pass through wall of villi into lacteals in lymphatic system, onto thoracic duct into bloodstream through subclavian vein

Where is the subclavian vein?

left side of neck

Digestion of lipids

subclavian vein transfers fatty acid and glycerol to liver, then oxidised for functions, excess stored as adipose tissue under skin

How to reduce fat intake

• reduce saturated fats

• choose low-fat dairy

• choose lean red meat and skinless chicken

• increase oily fish

• grill and steam, no fry

• choose fruit snacks