The Age Thickening of Sweetened Condensed Milk: IV. The Effect of Salts

Abstract

The effect of salts on the stability of simple colloidal sols is quite well understood. However, due to the complicated nature of the colloidal system of milk, their effect on the stability of the milk colloids is not so well understood, but has been investigated by a number of workers. Sommer (1) found that there is an optimum balance between the magnesium and calcium on one hand and the citrates and phosphates on the other hand in order to obtain the maximum heat stability of milk. Sommer and Binney (2) have shown that magnesium or calcium ions will change alcohol negative milk to alcohol positive milk, while citrate or phosphate ions will change an alcohol positive milk to alcohol negative. Sommer and Young (3) showed that with certain ice cream mixes the addition of sodium citrate or disodium phosphate before homogenization greatly increases the whipping ability and that additions of calcium lactate decrease the whipping ability. Henning and Dahlberg (4) found that the addition of sodium citrate and disodium phosphate to ice cream mixes before homogenization decreases the tendency of the fat globules to clump, decreases the viscosity of the mix and increases the whipping ability, while the addition of calcium salts has an opposite effect. They also showed that by the addition of potassium oxalate the calcium salts are precipitated and clumping is prevented entirely. North and Sommer (5) have shown that the electrical charge on the fat globules is involved in fat clu~nping and that the addition of positively charged ions decrease the charge on the globules and favors clumping while negatively charged ions have an opposite effect. Templeton and Sommer (6) reported that the whipping ability of whipping cream is increased by the addition of sodium citrate while calcium salts have an opposite effect. Traey and Ruehe (7) have demonstrated that calcium salts affect the feathering of cream in coffee and that feathering can be prevented by the addition of sodium citrate or disodium phosphate. The destabilizing effect of calcium on milk proteins has also been shown by the work of Van Slyke and Bosworth (8). They found that in neutralizing the excess of lime in a casein-lime-water solution with hydrochloric acid, Received for publication August 2, 1935. Published with the permission of the Director of the Wisconsin Agricultural Experiment Station.