Color Development in Lactose Solutions during Heating with Special Reference to the Color of Evaporated Milk

Abstract

Reproducible color standards for measuring the color of lactose solutions in which heat has produced varying shades of brown have been described and defined in numerical terms according to the Munsell system of color measurement. The presence of the phosphate radical in lactose solutions during heating has been shown to exert a specific effect in causing darkening in the color of these solutions. Color development in lactose solutions during heating is increased with increasing concentration of hydroxyl-ions, lactose, amino acids, ammonium salts, phosphate and oxygen. The presence of copper or iron catalyzes the color reaction while tin retards color formation. A very small quantity of formaldehyde increases color while larger amounts markedly restrict color development. Sodium bisulfite will entirely prevent the appearance of color. When amino acids or proteins are present during heating, color is probably due both to the formation of a complex material formed from the lactose and an amino group and to a polymerization of the sugar to lacto-caramel. Either reaction may occur at the hydrogen-ion concentration found in milk. An effective means of preventing color development in lactose solutions during heating which would be suitable for use in improving the color which appears in evaporated milk during sterilization was not found. However, the results obtained with lactose solutions substantiate the fact that the objectionable darkening in color of evaporated milk which occurs during storage can be materially lessened by shortening the storage period or lowering storage temperature. © 1935, American Dairy Science Association. All rights reserved.