Colloids Flashcards
What are colloids?
When one substance is dispersed through another but does not combine to form a solution
What is the disperse phase?
The substance which is dispersed
What is the continuous phase?
The substance the disperse phase is suspended in
What is a sol?
A liquid colloid in which solid particles are dispersed in a liquid phase. It is usually an unset product and is more liquid than solid
What is a gel?
A gel is a solid dispersed in a liquid but tends to be more solid than liquid and cool such as jelly
What is an emulsion?
A liquid dispersed in a liquid to form a stable liquid usually. Ie oil and egg make mayonnaise
What is a solid emulsion?
A liquid in a fat such as butter
What is a foam?
A gas in a liquid eg whipped cream
What is a solid foam?
Gas in a solid eg. Meringue, cake
Why might colloids become unstable?
The two phases may separate over time due to increased temp and physical force particularly fat and water
What is the continuous phase?
The substance the disperse phase is suspended in
What is a sol?
A liquid colloid in which solid particles are dispersed in a liquid phase. It is usually an unset product and is more liquid than solid
What is a gel?
A gel is a solid dispersed in a liquid but tends to be more solid than liquid and cool such as jelly
What is an emulsion?
A liquid dispersed in a liquid to form a stable liquid usually. Ie oil and egg make mayonnaise
What is a solid emulsion?
A liquid in a fat such as butter
What is a foam?
A gas in a liquid eg whipped cream
What is a solid foam?
Gas in a solid eg. Meringue, cake
Why might colloids become unstable?
The two phases may separate over time due to increased temp and physical force particularly fat and water
What is retrogradation?
A change which takes place once a gel has formed. The proportion of amylase in the starch affects the gelling properties. Amylose aids willing because the molecules are spiral shaped and form a network in which water is trapped
If a rigid gel is required high amylose starches are used
When foods are cooked and thawed or prepared for long term storage there is a risk of the amylase gel retrograding. The amylase molecules unwind and the gel becomes opaque and a pulpy sponge.
Manufacturers use high amylopectin starches to produce a strong gel that will not retrograde easily or a chemically modified starch
What is gelatinisation?
A suspension of starch in water is heated
The water penetrates the outer layers of the granule and they begin to swell at temps between 60-80C. The granules swell until there volume is almost 5x the original causing the mixture to become viscous
At 80C the starch granules break up and the endosperm becomes dispersed throughout the water
The long chain molecules unfold and viscosity increases forming a sol.
On cooling a network is formed with the water enclosed which produces a gel
Why do manufacturers use modified starch?
Prevent retrogradation and spoiling processed food products eg. Pie filling
Need processed foods to remain in good condition on shelves for several days - if they weep they are less desirable eg. Custard, white sauces
Two forms of starch - amylose = straight chain in coil, better gel but retrograde easier and amylopectin = highly branched reduces water loss and less retrogradation
Phosphoric acid gives amylose appearance but amylopectin properties
Modified starch is pre gelatinised and used in angel delight where thickening is instant on addition of cold water
Some starches are acid modified so clearer paste with less viscosity
