COLLOIDS
A colloidal system is a heterogeneous system they are mixtures that appear to be solution but are actually colloidal dispersions.
The material that forms the base of the system is called the dispersion medium or the continuous phase.
The material that forms the colloidal condition is called the dispersed medium or the discontinuous phase.
Since there are three states of matter-solid, liquid and gas-eight classes of colloids are formed. However, gases form solutions not colloids
Solid - liquid
Gas - liquid
Gas - solid
Solid – gas
Solid – solid
Liquid - solid
Liquid - gas
SUSPENSION
When the particles of solid are separated into large aggregates of particles and dispersed in a liquid the food system is referred to as a suspension. Egg- mixture of flour in water.
Depending on the relative affinity of the dispersed phase and the dispersed medium colloidal suspensions are of two types-
A. Lyophilic- solvent loving. For e.g. Water loving like skimmed milk, egg yolk, brewed coffee. These have high viscosity as there is more friction between the particles of the dispersed phase.
B. Lyophobic- solvent repelling. For e.g. Water hating like oil dispersed in water. These are less viscous.
SOLS:-
In a colloidal system, when solid particles are dispersed in a liquid and the colloid appears clear or opaque to the naked eye it is referred to as sol. However sols are not true solutions. Under the microscope, the dispersed particles are large enough to scatter and
Polarize the incident light to some extent. (This effect is called the TYNDALL EFFECT).for example-gelatin in water
Further when viewed under an ultra-microscope the colloidal particles are in a state of rapid and irregular movement this is called BROWNIAN MOVEMENT.
Altering the degree of dispersion of colloids-
In a sol having water as the continuous phase, the colloidal particles have an electrically charged surface. With the addition of a small amount of electrolyte (like sodium chloride that separate in water into + vet Na and –vet Cal) the oppositely charged ions are absorbed on the surface of each particle creating a potential difference between the surface of the particles and the solution. This is known as ZETA POTENTIAL. This stabilizes the system.
If an acid is added to the colloidal dispersion the dispersed phase precipitates (settles out) this is because of the ions released by the acid.
Other factors that affect the degree of dispersion of colloids are:-
FACTOR INCREASED DISPERSION DECREASED DISPERSION
Temperature Fat globules in milk Egg White coagulation
Mechanical Operation Gelatin in water Grinding, beating, stirring.
Acids Gluten in fermentation Acid in milk-curdles
Alkali Enzymes Gluten Proteinase increases
dispersion of Rennin gluten in flour In milk curdles
A colloidal system is a heterogeneous system they are mixtures that appear to be solution but are actually colloidal dispersions.
The material that forms the base of the system is called the dispersion medium or the continuous phase.
The material that forms the colloidal condition is called the dispersed medium or the discontinuous phase.
Since there are three states of matter-solid, liquid and gas-eight classes of colloids are formed. However, gases form solutions not colloids
Solid - liquid
Gas - liquid
Gas - solid
Solid – gas
Solid – solid
Liquid - solid
Liquid - gas
SUSPENSION
When the particles of solid are separated into large aggregates of particles and dispersed in a liquid the food system is referred to as a suspension. Egg- mixture of flour in water.
Depending on the relative affinity of the dispersed phase and the dispersed medium colloidal suspensions are of two types-
A. Lyophilic- solvent loving. For e.g. Water loving like skimmed milk, egg yolk, brewed coffee. These have high viscosity as there is more friction between the particles of the dispersed phase.
B. Lyophobic- solvent repelling. For e.g. Water hating like oil dispersed in water. These are less viscous.
SOLS:-
In a colloidal system, when solid particles are dispersed in a liquid and the colloid appears clear or opaque to the naked eye it is referred to as sol. However sols are not true solutions. Under the microscope, the dispersed particles are large enough to scatter and
Polarize the incident light to some extent. (This effect is called the TYNDALL EFFECT).for example-gelatin in water
Further when viewed under an ultra-microscope the colloidal particles are in a state of rapid and irregular movement this is called BROWNIAN MOVEMENT.
Altering the degree of dispersion of colloids-
In a sol having water as the continuous phase, the colloidal particles have an electrically charged surface. With the addition of a small amount of electrolyte (like sodium chloride that separate in water into + vet Na and –vet Cal) the oppositely charged ions are absorbed on the surface of each particle creating a potential difference between the surface of the particles and the solution. This is known as ZETA POTENTIAL. This stabilizes the system.
If an acid is added to the colloidal dispersion the dispersed phase precipitates (settles out) this is because of the ions released by the acid.
Other factors that affect the degree of dispersion of colloids are:-
FACTOR INCREASED DISPERSION DECREASED DISPERSION
Temperature Fat globules in milk Egg White coagulation
Mechanical Operation Gelatin in water Grinding, beating, stirring.
Acids Gluten in fermentation Acid in milk-curdles
Alkali Enzymes Gluten Proteinase increases
dispersion of Rennin gluten in flour In milk curdles
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