Some Relationships between pH, Titrable Acidity, and the Formol Titration in Milk Heated to High Temperatures

Abstract

Whole homogenized milk or skimmilk heated at 100[degree] C for periods up to 8 hrs., and at 116[degree]C for periods up to 2.5 hrs., were examined for acidity changes before and after adding oxalate, for formol titration changes before and after adding oxalate, and for pH changes. Na citrate and disodium phosphate were added to the skimmilk in certain trials. Acidity changes produced by the heat treatments were reduced upon oxalation in all except the phosphate-treated milk. Oxalate treatment of the phosphate samples resulted in higher titers, the difference being directly related to the length of the heating period. Formol titers were increased slightly by the heat treatments, but this increase was appreciably reduced in the normal samples upon addition of the oxalate and obliterated in the phosphate-treated milk. pH changes correlated well with the majority, but not with all of the titrations. Heating of whey at 116[degree]C produced changes which differed to some extent from those produced by heating milk. The comparative slopes of the acidity increase-heating time curves for normal- and oxalate-treated milk reveal that the first acidity increase in milk as detected by titration may be due to salt changes, resulting in an increase in the buffer capacity.