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 Krukovsky, V. N. Search for Related Content PubMed Articles by Krukovsky, V. N.

The Origin of Oxidized Flavors and Factors Responsible for their Development in Milk and Milk Products

Department of Dairy Industry, Cornell University, Ithaca, New York

ABSTRACT

In fresh milk the oxidized flavors such as chalky and chalky-to-soapy-tallowy have been demonstrated to be associated with the deterioration of milk plasma (skimmilk), and metallic and metallic-to-fishy flavors with the deterioration of the fat-globule membrane and oxidation-sensitive fat, respectively.

Evidence is presented that oxidative deterioration of the substances involved, which is stimulated in the presence of ascorbic acid and enhanced by Cu, is carried on preferentially. With passage of time, flavors developed in whole milk containing ascorbic acid and 0.1 to 0.4 mg. Cu per liter, changed from metallic to soapy-tallowy, the soapy flavor being dominant; with further increase in the Cu content from 0.5 to 10 mg. the soapy-tallowy flavors were superseded by metallic and metallic-to-fishy flavors associated with fat deterioration. Corresponding samples of reconstituted milk, from which the fat-globule membrane was removed, developed chalky-to-soapy-tallowy flavors first, which then were superseded by metallic and metallic-to-fishy flavors when the fat underwent deterioration as well. Only chalky and chalky-to-soapy-tallowy flavors developed in the skimmilk samples.

In contrast to this, in whole, skim and reconstituted milks totally depleted of vitamin 0 content by H₂O₂ and heat, 0.5, 1 and 5 mg. of Cu, respectively, were needed to promote the development of chalky flavor, and 5 mg. of catalyst to cause oxidative deterioration of fat.

The photochemical-heat destruction of vitamin C resulted in sensitization of milk to Cu catalysis of oxidized flavors. This effect was diminished when the fat-globule membrane was removed by separation of whole milk, followed by addition of pure stable fat to skimmilk thus obtained.

Oxidative deterioration of fat in presence of ascorbic acid and Cu was shown to be accompanied by oxidation of one double bond of the two double-bond fatty acids in the fat molecule.

The data indicate that the antioxidant activity of fat as determined by tocopherol content and extension of this activity to the body of milk by redistribution of fat, play an important part in the prevention of retardation of reactions which produce oxidized flavors.

The observations reported in this paper also explain the relative immunity of homogenized milk to oxidized flavors, since in such milk the fat remains scattered and the unstable lipid component of the fat-globule membrane is split and withdrawn from the surface into the interior of the fat-globules, where it is efficiently protected by the antioxidant.