FOOD TECHNOLOGYLIPIDS

CHEMICALS THAT MAKE UP FATS AND ITS FUNCTIONS

Carbon Hydrogen Oxygen

Functions Energy – 1g of pure fat provides 37KJ (9kcal) Formation of Adipose tissue – used as an Energy

reserve, Insulates and Protection Source of essential fatty acids Fat soluble vitamins: A,D,E,K

SOURCES OF FAT

Meat and Fish Confectionary Processed Foods Butter, Margarine, Lard Egg Yolk (Contains Cholesterol)

Uses of Food Production Creaming and Aerating Frying Shortening

CHEMICAL STRUCTURE

Fat belongs to a group of substances called Esters. Formed by the reaction between an alcohol and organic acid – known as fatty acids

Glycerol is a complex alcohol because it has 3 hydroxyl groups therefore known as a Trihydric Alcohol.

CHEMICAL STRUCTURE CONT.

Ester formed is a triglyceride. If all 3 fatty acids are the same, then Simple

Triglyceride is formed. If fatty acids are different then they are called Mixed

Triglyceride. Fatty acid Formula = R- COOH (‘R’ represents any

acid).

CIS AND TRANS FATTY ACIDS

CIS 2 hydrogen atoms on the same side of a double

bond.

Trans Hydrogen atoms on geometrically opposite sides of

the double bond.

SATURATED FATS

Occur when each carbon atom is attached to the surrounding atoms by a single bond.

The carbon atoms are completely saturated with hydrogen atoms.

Saturated fats have a melting point at about room temperature and are therefore usually hard – Could lead to heart disease and high cholesterol.

SATURATED FAT STRUCTURE

Carbon Atom

Hydrogen Atom

UNSATURATED FATS

Occur when some of the carbon atoms are joined to the surrounding hydrogen atoms by a double bond.

Monounsaturated fats have one double bond. Polyunsaturated fats have more than one double

bond. Unsaturated fats are mainly oils and have a melting

point at below room temperature.

Saturated Fatty Acid

Monounsaturated Fatty Acid

Polyunsaturated Fatty Acid

Palmatic Acid Oleic Acid Linoleic Acid

Stearic Acid Linolenic Acid

UNSATURATED FAT STRUCTURE

Double Bond

PROPERTIES OF FATS AND OILS

Solubility

Fats and oils are insoluble in water.

However, in the presence of a suitable substance known as an emulsifying agent, it’s possible to form a stable mixture of fat and water Emulsion.

The Emulsion may be a Fat – in – Water emulsion e.g. Milk

Or a Water – in – Fat emulsion e.g. Butter

Fats and oils are soluble in organic solvents such as petrol and carbon tetrachloride.

Solvents of this type can be used to remove grease and stains from clothing.

PROPERTIES OF FATS AND OILS

Plasticity

Fats do not melt at fixed temperatures, but over a range of temperatures.

This is because fats are mixtures of triglycerides (contain 3 different fatty acids), all with different melting points.

Some of the fatty acids forming the triglyceride will stay solid for longer than others.

This feature gives fat its plasticity that makes some fats spreadable.

E.g. Margarine – Has a wide range of plasticity and will spread from the fridge whereas most animal fat will have narrow plasticity and will not spread easily.

PROPERTIES OF FATS AND OILS

Effect of Heat

Oils and fats transfer heat well to foods being cooked but will eventually breakdown.

Heating causes the triglycerides to decompose. Melting Point

Fats melt when heated. Since fats are mixtures of triglycerides they do not have a distinct melting point but melt over a range of temperatures.

Temperature when melting occurs is known as the Slip Point.

Most fats melt at temperatures of 30°/40°C

Melting point for oil is below normal air temperature – The more double bonds, the lower the air temperature.

PROPERTIES OF FATS AND OILS

Smoke Point

When a fat or oil is heated to a certain temperature it starts to decompose, producing a blue haze or smoke.

Most fats and oils start to smoke at 200°C

Smoke Point for lard = 185°C

Corn Oil = 232°C

In general, vegetable oils have a higher temperature than animal fats.

Smoke is useful to measure when assessing the suitability of a fat or oil for frying purposes.

Repeated heating of a fat or oil will reduce the smoke point.

PROPERTIES OF FATS AND OILS

Saponification

Some triglycerides react with alkalis to form soap and a glycerol.

Hydrogenation

Some oils are so unsaturated in the natural state that they need to be treated to make them useful in food.

Hydrogenation is used to add hydrogen to the oil to break the double bonds. This makes the resulting fat more saturated and harder.

It is achieved by heating the oil in a large sealed vessel under pressure.

Hydrogenated fat makes TRANS fats which increases likelihood of cancer and free radicals in the body.

RANCIDITY

Used to describe the spoilage of fats and oils. Fat which is rancid will have an unpleasant smell and flavour.

Oxidative Rancidity

Reaction between unsaturated triglycerides and oxygen from the air.

Oxygen molecules join across the double bond of the triglyceride molecule and a variety of compounds are formed e.g. Aldehydes and Ketones – gives the unpleasant rancid taste.

Reaction is accelerated by heat, light and traces of metals e.g. copper/ iron.

RANCIDITY CONT…

Hydrolytic Rancidity

Enzymes known as lipase hydrolyse fats, breaking them down into glycerol and fatty acids.

Equation

Fat + Water Glycerol + Fatty Acids

Short Chains = More rancid

HOW TO STOP RANCIDITY

Keep fats free from oxygen and air. Keep metals and light away from fats. Do not store oil in iron containers use glass! Salt speeds up rancidity. Sugar slows down rancidity. Anti-oxidants can be used to slow rancidity.

USES IN FOOD PREPARATION

Frying

Fast cooking method – bad for health as it increases fat content, but tastes good.

Frying occurs at 180°C

Shortening

It’s an effect that fat has on a product – increases the crumbly texture of foods.

Stops the formation of effects of gluten.

Fat coats the flour preventing water making the flour stretchy. Creaming and Aerating

Adding air bubbles

Lighter colour

Increases volume – it rises due to trapped air.

PRODUCTION OF FATS AND OILS

Vegetable Oils

70% of all oils in the world are vegetable oils

It increases polyunsaturated fatty acids (PUFA). Margarine

An emulsion of water and fat.

The vegetable fat being used is first hydrogenated to give it some hardness (plasticity), and is then blended with skimmed sour milk, salt, colouring and Vitamins A and D (added by law).

Hard margarines are more hydrogenated then soft ones.

PRODUCTION OF FATS AND OILS

Spreads and Low Fat Spreads

Less then 80% fat

Increase water content – not suitable for cooking. Cooking fats and Shortening

First produced in USA as a substitute for lard and are pure fat products rather than emulsions.

Blended with fish oils, animal fats and are hydrogenated.

These fats are called High Ratio Fats and are designed for recipes e.g. Muffins

PROPERTIES OF FATS AND OILS CONT…

Lard

Extracted from pigs via heating OR ‘rendering’.

Almost 100% fat Butter

Churning of pasteurised cream, this causes the cream to become more viscous forming a solid butter.

Colour and salt is added to butter and is mixed for desired consistency.

Suet

Fat from around the kidneys of animals.

Sold in the form of shredded suet and used in Christmas puddings and Suet puddings.

CHOLESTEROL

A waxy white substance found in fats, particularly hard animal fats which can block arteries and be one of the causes of heart disease.

Cholesterol is carried around the body by specific proteins which come together to form a lipid – protein complexes called Lipoproteins.

High-density Lipoproteins (HDL) is beneficial because it transports cholesterol from places where there is too much, to the liver where it is disposed of.

Low-density Lipoproteins (LDL) can lead to deposits in the arteries (plaque) which causes narrowing.

ESSENTIAL FATTY ACIDS

Essential means that these substances cannot be made in the body so must be gained from food sources.

Two main types of essential fatty acids (EFA) are:

Polyunsaturated Fatty Acids (PUFA) – Linolenic and Linoleic acid.

Longer chain fatty acids: Arachidonic acid, EPA and DHA (these can be made in the body to a limited extent by linoleic acid and alpha linolenic acid)

EFAs are needed for:

The maintenance of cell membranes.

Hormone like substances called Eicosanoids (prostaglandins etc) which are involved in clotting blood.