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 Wells, P. R. Articles by Leeder, J. G. Search for Related Content PubMed Articles by Wells, P. R. Articles by Leeder, J. G.

Changes Related to Casein Precipitation in Frozen Concentrated Milk¹

Department of Dairy Science, Rutgers—The State University, New Brunswick, New Jersey

ABSTRACT

During storage of frozen concentrated skimmilk, lactose crystallization preceded protein precipitation. Cellulose acetate and free-boundary electrophoresis indicated that the precipitated protein was identical to normal casein. Casein precipitation was accompanied by losses of soluble calcium, phosphate, and citrate, but there was no change in the sodium or potassium content of centrifuged reconstituted milk. Precipitation occurred through interaction of the casein with colloidal tricalcium phosphate in the unfrozen portion.

Cooling of concentrated skimmilk with agitation before freezing hastened lactose crystallization and subsequent casein precipitation, but quiescent cooling and freezing yielded a more stable product. The quiescently frozen samples were more stable when stored at +15 F than at +5 F, but samples cooled with agitation deteriorated more rapidly at the higher temperature.

Glucose, fructose, sucrose, sorbitol, and citrate delayed lactose crystallization in frozen concentrated skimmilk and protected casein from precipitation, once crystallization had occurred. Carboxymethylcellulose and glycerol delayed lactose crystallization but did not protect casein.

In fluid skimmilk systems containing 2 M KCl and 0.1 M (NH₄)₂HPO₄, added glucose, fructose, sucrose, lactose, and sorbitol delayed casein gelation and maintained ultrafiltrable calcium at higher concentrations than in controls containing no added carbohydrate. Eesults of this investigation suggest that sugars hinder the interaction of colloidal Ca₃(PO₄)₂ with the casein micelle.

¹ Paper of the Journal Series, New Jersey Agricultural Experiment Station, Rutgers—The State University, New Brunswick, New Jersey.

² Present address: Colgate-Palmolive Research Center, New Brunswick, New Jersey.