Lipids

Question 1

Acylglycerol

Answer 1

Fatty acids esterified to glycerol
Most abundant lipids in food
1-3 Fatty acids per glycerol
Most commonly found as triacylglycerol
Can contain saturated and unsaturated

Question 2

Common lipids in food

Answer 2

Acylglycerol
Glycolipids
Phospholipids
Terpenes - cholesterol and cholesterol esters

Question 3

Fats

Answer 3

Solid at room temperature
Animal fats - saturated, milk or body fats
Vegetable fats - tropical seeds - coconut, palm`

Question 4

Oil

Answer 4

Liquid at RTP
Marine oil - long chain FA
Vegetable oil - High in unsaturated

Question 5

Properties of fats

Answer 5

Mixtures of TAG
Fats are semi-solid at room temp
Solid part due to crystalized TAG
TAG crystals exhibit polymorphism - exist in more than ones form
At high temp - all TAG are liquid
As temperature decreases more TAG crystallise
Rate at which cools defeminise solid fat content
Faster cooling rate increased solid content

Question 6

Melting Point

Answer 6

As temp increases, fat gradually becomes softer as each constituent melts
While fat melts there is a large change in heat content for a small rise in temperature (heat of fusion)

Question 7

Solid fat index

Answer 7

Solid:Liquid
Given temperature below melting point
Not one melting point due to the range of fatty acids

Question 8

Cocoa Butter structure

Answer 8

Has three major fatty acids
6 polymorphic forms
I - has lowest melting point
VI - has highest
Type V is most desired

Question 9

Type V Cocoa Butter

Answer 9

Shrinks when cooled - comes away from moulds
Melts at mouth temp
Glossy
Smooth

Question 10

Chocolate Blooms

Answer 10

Grey colour on chocolate
Occurs when stored below 17 degrees
Caused by type VI crystals
Type V transforms to VI at room temp instantly when heated to 35 degrees

This is why chocolate is tempered

Question 11

Tempering

Answer 11

Completely melt chocolate 60-65 degrees
Cool to crystallise 22-25
Reheat to 29-31
Cool to 5-10
Store 13-17

Question 12

Hydrogenation

Answer 12

Decreased number of unsaturated bonds
Makes fat more like plastic
Plasticity - change shap when pressure applied then keep new shape when pressure removed
Increased stability of a fat decreasing its tendency to oxidise

Expose oils to hydrogen gas at high temp
140-225 degrees
Pressure 2-10atm
Nickel catalyst

Makes more trans
Double bond sometimes moves along chain

Question 13

Lipolysis

Answer 13

Release free FA from a TAG
Gives rise to hydrolytic rancidity
Unpleasant taste due to increasing acidity

In animals there is little lipolysis
In plant oils there is more due to lipase enzymes - extracted oils are neutralised with alkali

Non-enzymic lipolysis - associated with deep fat frying