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. Search for Related Content PubMed Articles by Gould, I. A.

Lactic Acid in Dairy Products. III. The Effect of Heat on Total Acid and Lactic Acid Production and on Lactose Destruction¹

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

ABSTRACT

Whole milk and skim milk, heated in sealed cans at 100°C. for periods up to 8 hours, and at 116°C. for periods up to 2.5 hours, were examined for increases in titrable acidity by electrometric titration, lactic acid by essentially the Hillig colorimetric method, and lactose by the polarimetric procedure. In certain trials, 0.3 per cent sodium citrate or disodium phosphate was added to the skim milk prior to heating.

The lactic acid produced by these treatments was within the ranges of 3 to 7 mg. per 100 gm. of milk and constituted only 5 per cent or less of the total acid produced as determined by titration. The presence of the stabilizing salts during heating appreciably increased the titrable acidity, but increased the lactic acid by not more than 2 to 3 mg. per 100 gm.

Lactose destruction, as a result of these heat treatments, amounted to about 25 to 30 per cent of the total lactose in the normal samples. Greater destruction occurred when the citrate or phosphate was present.

The slight increase in lactic acid as a result of heat treatment indicates that the use of proper lactic acid measurements on fresh concentrated milk products may be relied upon to reveal the quality of the raw milk used in their manufacture.

The heating of whey for 2.5 hours at 116°C. resulted in only about 11 per cent as much increase in titrable acidity as in skim milk, but losses in lactose and increases in lactic acid were similar.

The possibility exists that methods of analysis which may be acceptable for normal milk may not always yield reliable results when applied to milk which has been altered by high-temperature heat treatment.

¹ Journal Article No. 732, new series, from the Michigan Agricultural Experiment Station.

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