High-Temperature Short-Time Sterilized Evaporated Milk. III. The Influence of the Lipid Phase on Heat and Storage Stability

Laboratory experiments in which high temperature-short time sterilization of concentrated milk was carried out under static conditions showed that heat and storage stability were at times adversely affected by the presence of a lipid phase. Three types of milk were encountered. The predominant type (if forewarming was employed) consisted of milks in which the fat phase behaved as an inert phase, that is, the processed whole and the corresponding processed skimmilks were heat-stable and resisted gelation during storage to approximately the same degree. On occasions, a type of milk was encountered in which the processed whole but not the corresponding processed skimmilk coagulated during sterilization. On other occasions, a type of milk was met in which the processed whole milk had a slightly greater / shelf-life than the corresponding processed skimmilk. Exchanging the fat globules belonging to a heat-stable for those in a heatlabile milk tended to reverse the order of stability. Substitution of fat for an equal weight of protein showed that both heat stability and storage stability were significantly decreased by the substitution. Milks prone to coagulate because of an unstable lipid phase were stabilized to some extent by forewarming against both heat coagulation and gelation during storage. Mixing of forewarmed and unforewarmed milks resulted in composite milks with heat and storage stabilities intermediate between those of the unmixed milks. Milks reconstituted from butter oil and skimmilk were stabilized by the addition of fatsoluble interfacially active mixtures to the butter oil.