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Journal of Dairy Science Vol. 32 No. 4 334-344
© 1949 by American Dairy Science Association ®
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Some Factors Influencing the Reducing Systems in Dry Whole Milk1

H. A. Harland, S. T. Coulter and Robert Jenness

Divisions of Dairy Husbandry and Agricultural Biochemistry, University of Minnesota, St. Paul

ABSTRACT

Data have been presented indicating the source of thiamin disulfide reducing substances (TDRS) in heated milk and their relationship to acid ferricyanide reducing substances (APRS) as well as to the keeping quality of the dry whole milk. The influence of the oxygen tension and the concentration of the system on the production of TDRS and AFRS during the heat treatment have been studied.

The nitroprusside and thiamin disulfide methods for sulfhydryl groups in milk have been compared.

The following conclusions may be drawn from the results secured:

  1. The substances that reduce thiamin disulfide are derived from the heat treatment of serum proteins and represent only a portion of the materials oxidized by ferricyanide.
  2. The thiamin disulfide reducing substances appear to be associated with increased resistance to oxidation when present in dry whole milk but do not decrease in quantity as the milk fat is oxidized.
  3. The presence of oxygen in milk being preheated depresses the amount of reducing substances produced.
  4. The rate of production of thiamin disulfide reducing substances decreases with increase in the solids content of heated milk and becomes negligible at solids concentrations exceeding 60 per cent.
  5. The rate of production of acid ferricyanide reducing substances in heated nonfat milk solids reaches a maximum at about 90 per cent solids.
  6. The thiamin disulfide and nitroprusside reagents measure the same or parallel reducing systems in heated milk.

FOOTNOTES

1 Paper no. 2439, Scientific Journal Series, Minnesota Agricultural Experiment Station, St. Paul.






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Copyright © 1949 by the American Dairy Science Association ®.