The Interrelationships of Processing Treatments and Oxidation-Reduction Systems as Factors Affecting the Keeping Quality of Dry Whole Milk1,2

Abstract

Summary High-temperature-short-time treatments (90 to 96° C. for 60 to 80 sec.) are superior to 30 min. at 76.7 to 96° C. for preheating fluid milk for drying purposes. The short-time preheating results in lower oxidation-reduction potentials, less oxidation of ascorbic acid and greater retention of iodosobenzoate and thiamine disulfide-reducing substances in both the fluid and dry product. Furthermore, dry whole milk prepared with the short-time preheating exhibits better resistance to oxidation during storage. The removal of oxygen from the system previous to a 30-min. heat treatment at 85° C. results in lower Eh values, better retention of thiamine disulfide-, acid ferricyanide- and iodosobenzoate-reducing substances than if the heating is done in air or in equilibrium with oxygen. There is a close relationship between the content of thiamine disulfide-reducing substances and the resistance of dry whole milk to oxidation during storage in air if HTST preheating is used. The initial redox potential, the content of ascorbic acid, acid ferricyanide- (AFRS), thiamine disulfide- (TDRS) or iodosobenzoate-reducing substances (IBRS) used individually are not reliable indices of the resistance of dry whole milk to oxidation. The estimation of both the IBRS and TDRS contents of fresh samples may be of value in estimating the storage life of dry whole milk.