Effect of milk solids concentration on the pH, soluble calcium and soluble phosphate levels of milk during heating.

摘要

When milk is processed to dairy products, concentration of the milk and the temp./time combinations to which the milk is exposed can be varied. For example, large differences in milk concentration and temp./time combinations are used in the manufacture of milk powder or the various concentrated liquid milk products. Although the milk salts, particularly the concn. and equilibrium states of Ca and inorganic phosphate, are considered to be important in the stability and functionality of dairy products, there have been few studies on the mineral balance in concentrated milk systems and how this is affected by temp. changes. Thus, this study examined the effect of milk concentration (9.6-38.4% w/w TS), temp. (20-80 degrees C) and time (0-60 min) on the pH value and the levels of soluble Ca (Casol) and soluble inorganic phosphate (Psol). At any given temp., levels of Casol and Psol, as mmol kg-1, increased and the pH value decreased with increasing milk concentration. However, when measured as a percentage of the total, levels of Casol and Psol decreased with increasing milk concentration. At any given milk concentration, levels of Casol, Psol and milk pH decreased within the 1st few minutes of heating, with little further change at longer heating times. For milk samples at each concentration examined, there was a strong correlation between the final Casol level and the final Psol level at all temp. At any particular milk concentration, there was a strong correlation between the final milk pH value and the final Casol or final Psol level. These results indicate that substantial decreases in milk pH value, Casol level and Psol level can occur at the temp. to which milk is exposed during common commercial processing, and that the extent of these changes will be dependent on milk concentration and processing conditions.