Fundamentals of Food Technology

Classification

Colloids are classified into two groups
(1) Lyophobic colloids
(2) Lyophilic colloids.


• The lyophobic colloids which have no affinity for water (e.g. inorganic colloids) while the lyophilic organic colloids such as proteins, starch, etc. which have greater affinity for water.
Food Sols and Gels

• Colloidal dispersions of proteins or polysaccharides may be broadly divided into two groups (1) sols and (2) gels.
• Sols are free flowing liquids at room temperature while gels are relatively firm and do not flow from a spoon.

Food Sols

• Food sols are dispersions of colloidal particles with diameters 1 mµ to 100 mµ.
• Typical examples are solution of egg albumen in water and dilute solution of gelatin in water.

Rheology

• The viscosities of hydrophilic sols are much greater than that of water.
  
• The increase in the concentration of the colloids increases the viscosity of the sols.

Food Gels

• A food gel consists of a continuous phase of inter-connected macromolecules intermingled with a continuous liquid phase such as water.
• Common food gels are fruit jelly, gelatin gels and starch gels.
• Gels possess varying degrees of rigidity and elasticity, depending on the type and concentration of gelling agent.

Syneresis of gels

• The spontaneous exudation of liquid from a gel is called syneresis (weeping).
• This phenomenon occurs sometimes in fruit jellies due to defective formulation of the product.