FOOD LOVELITA

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FORCE BETWEEN COLLOIDAL PARTICLES

IMK 209PHYSICAL PROPERTIES OF FOOD

Types of electrostatic

Van der waals attractive force is tends to destabilise colloids.

Electrostatic repulsive forces is generally impart stability.

DLVO Theory DLVO stand for Derjaguin-Landau-Verwey-Overbeek) Colloid stability proposes a balance of the :

repulsive electric double layer forces (+ve by convection)attractive Van Der Walls force (-ve by convection)

In the other word, the DLVO theory states that the stability of a colloidal suspension depends on the net interaction forces between the dispersed particles :Van Der Walls force of attractionThe electrostatic repulsion between electrical double layers of identical sign

Electrical Double Layer

Region of unequal counter and co ion concentrations near the surface.

Regarded as consisting of two regions :An inner region of strongly adsorbed ionsOuter region where ions are diffusely distributed according to a balance between electrical forces and random thermal motion.

The formation of a double layer is very important for the stability of the colloid.

The double layer is sensitive to electrolytes and also temperature.

This means that the stability of the colloid may be manipulated by adding electrolytes or changing the temperature

Zeta Potential

Electrical potential on the surface of the diffuse layer i.e. slipping plane(hydronamic plane of shear).

At some point out in the double layer region,corresponding more or less to the potential at the zone of shear,electrical potential.

Value : < -15mV ( represent onset of flocculation)

Value more negative than 130mV (stability dividing line)

Range -15mV to -30mV cannot categorically state –emulsion will or not be stable at given zeta potential

Effect of ionic strength & pH Lower the concentration of inorganic electrolytes (salts),

the higher will be the repulsive energy and the more stable the emulsion toward flocculation (aggregation).

Compromises between flavour and stability. When ( salt ) more certain critical value

( depends on type of food system ) thickness of double layer.

Will decrease- chances for droplets come close together increase.

When ( salt ) less than critical value, optimum thickness of double layer obtained, so emulsion is stabilize.

Compressed by the the salt and hydrogen ion concentration .

Make the repulsive force ineffective . Droplet charge decrease stabilized

emulsions-ph tends toward isoelectric point. Protein stabilized emulsions become

aggregate when ph adjust protein isoelectric point.