Observations on the Ascorbic Acid Content of Evaporated Milk

Abstract

The ascorbic acid content of evaporated milk has been investigated by Meulemans and de Haas (9), who concluded that the canned product contains as much vitamin C as does p r e p a r e d fresh milk. These workers apparently used a direct titration procedure with 2,6-dichlorobenzenoneindophenol and obtained data ranging from 20 to 30 rag. per liter of ascorbic acid in evaporated milk reconstituted to a fluid basis. Henry, Houston, Kon and Osborne (3), using the precipitation technique of Kon and Watson (8), titrated milk serum with the indophenol dye and found losses of about 30 per cent in the total ascorbic acid content of evaporated milk due to manufacture, with a subsequent gradual loss in storage. Appreciable quantities of dehydroascorbic acid were noted upon reduction of the milk serum with hydrogen sulfide, scrubbing with nitrogen and subsequent titration. Woessner, Elvehjem and Schuette (13) found only insignificant amounts of dehydroascorbic acid in evaporated milk using a photoelectric method and extrapolating galvanometer readings to zero time, which procedure they found corrected errors due to spurious reducing substances resulting from the effect of hydrogen sulfide on milk ingredients other than dehydroascorbic acid. These workers state that the metallic nature of the manufacturing equipment is not related to the ascorbic acid content of evaporate(~ milk nor are the use of stabilizing salts, the degree of preheating or geographical considerations. Kon and Henry (7) noted a loss of 43 per cent in the ascorbic acid content of fresh fluid milk as a result of sterilizing at a temperature of 230 ° F., whereas Josephson and Doan (5) showed that moderately high temperatures (170 ° F. to boiling) cause a stabilization of the ascorbic acid of milk as a result of heat produced, sulfhydryl, reducing substances derived from certain milk proteins.