role of psychotropic bacteria in raw milk on stability of milk proteins to UHT treatment

ABSTRACT

The effects of psychrotrophs growth on proteins of raw skim milk and the response of milk proteins to UHT-treatment were studied. 4 psychrotrophs isolated from raw milk attacked raw skim milk proteins. k and B-caseins were most susceptible although some of the isolates also attacked the whey proteins. Growth of psychrotrophs in raw skim milk predisposed the proteins to deleterious effects of UHT-treatment. Ultrahigh temperature had little effect on raw skim milk caseins while, decreased alpha-lactalbumin and B-lactoglobulin by 22% and 36%, respectively. Milk that had undergone proteolysis exhibited decreased detectable k-, B-, and alpha S-caseins but increased loss of B- lactoglobulin as a result of UHT-treatment. Milk suffering extensive k-casein degradation coagulated during UHT-treatment. Coagulation during or shortly after heating increased with severity of heat treatment and size of psychrotrophs population