Gelatin, protective action

All hydrophilic colloids possess some degree of protective action and gelatin, starch and casein are used commercially for this purpose. 

On account of the tendency of the suspended particles to eoalesec, colloidal solutions of sulphur are generally short-lived. The stability of the solutions can be increased by the addition of a protective colloid such as albumen or gelatine. The action of hydrochloric acid on sodium thiosulphate solution yields a colloidal solution which is more stable if the reagents are used in a concentrated condition,0 but the life of the unstable colloidal solution obtained with dilute reagents can be extended by the addition of gelatine. Also, by preparing tire sulphur in a wet way in the presence ol albumen, the... 

Add I cm3 of a 0.1% solution of gelatine to about 10cm3 sol and repeat the above flocculation experiments. Observe the protective action of gelatine. 

The protective action of gelatin on the precipitation of colloidal gold was noticed by Faraday (see p, 729). Zsigmondy represented the protective action of a colloid by a gold number . Protective colloids (sodium lysalbinate, prepared from albumin, etc.) were used by C. Paal to prepare colloidal silver containing 93 per cent, of silver but soluble in water. The protective action is probably due to adsorption. 

The colloidal nature of soap solutions is manifested by the protective action on gold solutions. The gold number of sodium oleate lies between 0.5 and 2. The protective effect is therefore about as great as that of gum arabic, and much smaller than that of gelatin. The protective effect of sodium stearate increases with the temperature. 

The most conspicuous influence of the addition of lyophilic colloids to lyophobic ones is the protective action" A sufficient (usually not very large) quantity of , for instance, gelatin makes a lyophobic sol much less susceptible to flocculation by electrolytes Electrophoresis measurements show that the electrophoretic velocity of the hydrophobic particles has changed by the addition of the gelatin from the value of the pure hydrophobic sol to a value proper to the pure gelatin soL... 

The mechanism of the breaking of the protected gelatine emulsion with soda is by no means clear. On the assumption that the gelatinate ion exerts but little stabilising action on the emulsion... 

Attempts have been made to estimate the proportion of B-fraction by removal of the A-fraction through hydrolysis with various enzymes. Since it is now recognized that the B-fraction undergoes partial conversion, these estimates are of little value. Treatment of gelatinized cereal starches with certain amylases gives a flocculent precipitate, variously termed hemicellulose or amylocellulose. This appears to be a degraded A-fraction, rendered insoluble through adsorption of fatty acids present in the substratum and also by deterioration of the protective colloid action afforded by the B-fraction. 

After removal from solution, CCCs are gelatinous and easily damaged by mechanical or chemical action. Immediately after CCC formation, it is possible to wipe the deposit off of a metal surface with a sponge. If a CCC is to be used for stand-alone corrosion protection, it is usually allowed to harden for at least 24 h before any further handling [109]. However, as CCCs... 

Many vitamins are destroyed by oxidation, a process speeded up by the action of heat, hght and certain metals such as iron. This fact is important since the conditions imder which a food is stored wiU affect the final vitamin potency. Some commercial vitamin preparations are dispersed in wax or gelatin, which act as a protective layer against oxidation (for further details of vitamin supplementation of diets, see Box 5.1). 

Davis, P. (1958) The giianidino side chains and the protective colloid action of gelatin, in G. Stainsby, ed.. Recent Advances in Gelatin and Glue Research, Pei amon press, London, pp. 225—230. 

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