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Journal of Dairy Science Vol. 13 No. 2 140-157
© 1930 by American Dairy Science Association ®
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{alpha} and ß Lactose in Some Milk Products

H. C. Troy and Paul Francis Sharp

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

ABSTRACT

  1. Between the pH values of 2.0 and 7.0 the rate of change of {alpha} and ß lactose into each other is at a minimum. The rate approaches infinity at pH 0.0 and 9.0.
  2. The effect of pH on the rate of change of {alpha} to ß lactose was shown to influence the rate of solution of {alpha} lactose hydrate and the effect of pH on the rate of change of ß to {alpha} lactose was shown to influence the rate of precipitation of {alpha} lactose hydrate at 25°C.
  3. Relatively concentrated sucrose solutions have little effect on the rate of change of the two forms of lactose into each other at 25°C.
  4. Lactose was found to be in a non-crystalline equilibrium mixture of the {alpha} and ß forms in skimmilk dried by the pressure and centrifugal spray and by the atmospheric and vacuum drum methods, when freshly prepared and maintained at a low moisture content. A considerable amount of {alpha} lactose hydrate was found to have crystallized in skimmilk during drying by the flake process.
  5. The caking of milk powder is believed to proceed as follows:
  6. the absorption of moisture by the concentrated lactose syrup,
  7. the adherence of the milk particles to one another, and (3) the solidification of the mass due to the crystallization of some of the lactose as {alpha} hydrate.
  8. The formation of "sandy" ice cream was explained as being due to the presence of sufficient non-frozen water to permit the {alpha} lactose hydrate to crystallize. By rapidly freezing out the water from ice cream, the lactose solution may be concentrated to a region where the crystallization of the {alpha} lactose hydrate does not occur, {alpha} lactose hydrate crystals form in such ice cream if sufficient ice is melted to dilute the syrup to a range of concentration where crystallization can take place.
  9. The Hudson and Brown seeding test was shown to be useful for recognizing the presence of crystalline {alpha} lactose hydrate in dairy products.
  10. Lactose was found to be present in the dry residue of the total solids determination in milk as an equilibrium mixture of {alpha}and ß lactose in the non-crystalline condition.
  11. It was found that nearly all of the lactose crystallized out as the {alpha} hydrate form when milk was dried very slowly at 50°C.




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H. K. Vyas and P. S. Tong
Process for Calcium Retention During Skim Milk Ultrafiltration
J Dairy Sci, September 1, 2003; 86(9): 2761 - 2766.
[Abstract] [Full Text] [PDF]


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