The Effect of Lactose Crystallization on Protein Stability in Frozen Concentrated Milk

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Abstract
Coagulation of the colloidal Ca casemate in frozen concentrated milk is initiated by spontaneous crystallization of the lactose at freezing temps. above -20[degree]F. Lactose crystallization and colloid destabilization are suppressed at -20cF, at which temp. calorimetric measurement indicates substantially complete freezing. At freezing temps. which permit dilution of the amorphous lactose with unfrozen water both lactose crystallization, measured polarimetrically, and casein coagulation are accelerated to the same extent. Reduction of the level of lactose supersaturation in frozen concentrated milk, by enzymatic hydrolysis of the lactose, inhibits lactose crystallization and stabilizes the colloid system. It is suggested that lactose in the metacryotic phase of frozen milk may intercept the casein coagulating action of the concentrated Ca salts by sequestration. Withdrawal of the moderating influence of soluble lactose as a consequence of its crystallization may thereby induce coagulation of the colloidal casein.