Lipids Flashcards
Acylglycerol
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
Common lipids in food
Acylglycerol
Glycolipids
Phospholipids
Terpenes - cholesterol and cholesterol esters
Fats
Solid at room temperature
Animal fats - saturated, milk or body fats
Vegetable fats - tropical seeds - coconut, palm`
Oil
Liquid at RTP
Marine oil - long chain FA
Vegetable oil - High in unsaturated
Properties of fats
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
Melting Point
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)
Solid fat index
Solid:Liquid
Given temperature below melting point
Not one melting point due to the range of fatty acids
Cocoa Butter structure
Has three major fatty acids 6 polymorphic forms I - has lowest melting point VI - has highest Type V is most desired
Type V Cocoa Butter
Shrinks when cooled - comes away from moulds
Melts at mouth temp
Glossy
Smooth
Chocolate Blooms
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
Tempering
Completely melt chocolate 60-65 degrees Cool to crystallise 22-25 Reheat to 29-31 Cool to 5-10 Store 13-17
Hydrogenation
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
Lipolysis
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