Wednesday, August 21, 2013

Gold Number

The lyophilic colloids differ widely in their power of protection. The protective action of different colloids is measured in terms of the Gold number introduced by Zsigmondy. The gold number is defined as:
“The number of milligrams of a lyophilic colloid that will just prevent the precipitation of 10ml of standard gold sol (containing 0.5 to 0.6gm of gold per litre) when 1 ml of 10% sodium chloride solution is added”.
         The precipitation of gold sol is indicated by a colour change from red to blue. (When the particle size increases colour changes). The smaller the gold number of lyophilic colloid, the greater is its protecting power. Geletin has small gold number and is an effective protective colloid.

The gold number of few protective colloids is as follows:

Geletine = 0.005 – 0.01
Haemoglobin = 0.03 – 0.07
Egg Albumin = 0.08 – 0.10
Gum Arabic = 0.10 – 0.15
Potato Starch = 25
Casein = 0.01 – 0.02

In the preparation of ice cream, geletin is used as protecting agent to the colloidal particles of ice. If the ice particles coagulate, the smooth texture of ice cream is lost.

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