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Bound Water and its Relation to Some Dairy Products

I. The Bound Water Content of Some Milk Products and Other Products Used in the Dairy Industry¹

Department of Dairy Husbandry, The Pennsylvania State College

ABSTRACT

The cryoscopic method can be readily used for the determination of bound water in liquid dairy products with few exceptions.

Milk, cream and other liquid dairy products contain appreciable amounts of bound water. In a milk of average fat and total solids content, the casein binds approximately 50 per cent of the bound water, the albumin 30 per cent, the fat globule "membrane" 15 per cent, and the remaining solids less than 4 per cent.

There is some indication that rennet casein binds more water than acid casein and therefore this fact may contribute to some of the differences of the two caseins.

More water is bound by the true hydrophilic colloids (whey proteins) of milk at a pH 6.6 than at a pH 4.7. Dialyzed whey protein bind as much water as natural whey proteins found in milk. Lactose does not affect bound water determinations of liquid dairy products with the cryoscopic method.

A large portion of the bound water present in cream is due to the hydrophilic properties of the fat globule "membrane" and in cream containing between 18 and 40 per cent butterfat the bound water content per gram of solids remains fairly constant.

The fat globule membrane binds approximately the same amount of water as the casein. Pure milk phospholipids are found to be the most hydrophilic of any substances isolated from milk in this study. Pure egg phospholipids are less hydrophilic than the pure milk phospholipids.

In this study the bound water content of gum arabic appears to be almost a linear function of concentration. The colloidal extract of oat flour (Avenex No. 7) is not very hydrophilic. Powdered egg yolk, locust bean flour and "colace" bind relatively large quantities of water while gelatin and sodium alginate give negative results, in some instances, with the cryoscopic method.

¹ Authorized for publication on December 7, 1937, as paper No. 804 in the Journal Series of the Pennsylvania Agricultural Experiment Station.

² The data presented in this paper are from, a thesis submitted to the Graduate School of the Pennsylvania State College in partial fulfillment of the degree of Doctor of Philosophy, 1937.