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Effect of Certain Salts on Precipitation of Casein by Calcium Chloride and Heat

1957; Elsevier BV; Volume: 40; Issue: 3 Linguagem: Inglês

10.3168/jds.s0022-0302(57)94475-2

1529-9066

Charles A. Zittle, E.S. Della Monica, J.H. Custer,

Food Science and Nutritional Studies

Casein was precipitated by calcium chloride and heat.It dissolved again at lower temperatures in the presence of sodium chloride and citrate but not in phosphate.Heat precipitation of casein by calcium chloride was prevented by excess citrate or phosphate and much less precipitation occurred with sodium chloride.Sodium phosphate was more effective in preventing casein precipitation at pH 6.6 than at 6.1, as more calcium phosphate was formed at the higher pH.Editor.Precipitation of casein by calcium chloride and heat and the subsequent re-solution of the precipitate at lower temperature has been reported (13).The possible relationship of this phenomenon to the drop in viscosity of evaporated milk in storage was discussed (13).To relate the observations more directly to the heating of milk, the effects of sodium chloride, citrate, and phosphate on this precipitation reaction have been studied, because of the presence of these salts in milk and also because of the use of the latter two as milk stabilizers. MATERIALS AND METttODSCasein was prepared and the solutions were made as described previously (13).The pH values were adjusted after the salts or other reagents were added.Heating of the samples, centrifuging, sampling, and determination of the casein by light absorption at 280 m~ have been described (13).Viscosity was determined in a Bingham type viscometer.Details of the measurement have been reported (12).Calcium was determined by the murexide (ammonium purpurate) method (11) ; phosphate in the concentrations used in these experiments did not interfere.Phosphorus was estimated with the ammonium molybdate reagent after reduction with ferrous sulfate. RESULTS Sodium chloride.The ability of increasing quantities of sodium chloride to reduce the precipitation of calcium and sodium caseinates by calcimn chloride and heat is shown (Figures 1 and1A).For the calcium caseinate experiments, calcium chloride was added to 2% calcium easeinate to give the total calcium