Seasonal Variations in the Heat Stability of Concentrated Milk: Effect of Added Phosphates and pH Adjustment

¹ Centre de recherche STELA, Départment de sciences et technologie des aliments, Universté Lava, Pavilion Paul-Comtois, Ste-Foy, PQ, Canada G1K 7P4
² Centre de recherche et développement sur les aliments, Agriculture Canada, 3600 Boul. Casavant ouest, St-Hyacinthe, W, Canada J2S 8E3

Natural variations in heat stability of 31% total solids concentrated milk have been surveyed over a 1-yr period. Very small variations occurred, and no distinctive instability period was observed. The stabilizing effect of pH adjustment with NaH₂PO₄·Na₂HPO₄ or NaOH·HC1 before sterilization was studied. The phosphates produced better stabilization than the acid-base combination at any pH between 6.0 and 7.0. The effectiveness of Na₂HPO₄ showed seasonal variations: the effects were marked on summer milks and smaller in winter milks. Conversely, seasonal variations were observed in the buffer capacity of the concentrates. The results emphasize the possibility of a specific stabilization mechanism by phosphate salts on concentrated milks.

Key Words: heat stability • concentrated milk • stabilizers

Submitted on October 26, 1989
Accepted on November 2, 1990