HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Gould, I. A. Articles by Frantz, R. S. Search for Related Content PubMed Articles by Gould, I. A. Articles by Frantz, R. S.

Some Relationships between pH, Titrable Acidity, and the Formol Titration in Milk Heated to High Temperatures¹

Agricultural Experiment Station, Michigan State College, East Lansing, Michigan

ABSTRACT

Whole homogenized milk or skim milk heated at 100° C. for periods up to eight hours, and at 116° C. for periods up to 2.5 hours, was examined for acidity changes before and after adding oxalate, for formol titration changes before and after adding oxalate, and for pH changes. Sodium citrate (0.3 per cent) and disodium phosphate (0.3 per cent) were added to the skim milk in certain of the trials. Titrations were conducted electrometrically.

Acidity changes produced by the heat treatments were reduced when the milk was treated with oxalate prior to titration in all milk excepting that containing added phosphate. The oxalate treatment of the phosphate milk, however, resulted in higher titers, the difference being more marked as the heating period progressed.

The heating of milk under the conditions of these experiments resulted in a slight, but definite, increase in the formol titration. This increase was appreciably reduced in the normal samples upon the addition of oxalate, whereas in the phosphate samples it was completely obliterated.

pH changes correlated well with the majority, but not with all of the titrations. Changes in the buffer capacity of milk, as produced either by the addition of salts or through heat may influence the titration without a similar influence on the pH.

Heating of whey at 116° C. produced changes which varied from those produced by heating milk. The whey exhibited greater increases in formol titration than did the skim milk from which it was obtained, and the formol titration increase was unaffected by treatment of the whey with oxalate. This may indicate that the salts which are responsible for an important portion of the formol titration increase are associated with, and removed with, the casein in the preparation of the whey.

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.

¹ Journal Article No. 734, new series, from the Michigan Agricultural Experiment Station.

² Now at the University of Maryland, College Park, Md.