CASEIN-BOUND PHOSPHORUS AND CONTENTS OF F REE AMINO-ACIDS IN MILK SUBJECTED TO DIFFERENT HEAT-TREATMENTS

In view of the technological and nutritive importance of heat-induced changes of the milk proteins the influence of heat treatment of milk o n the content of casein-bound phosphorus and the free amino acids (FAA ) has been investigated.Dephosphorylation of casein takes already plac e at temperature/time combinations which correspond to a sterilization value of 1.9 min, i.e. in the upper region of high temperature pasteu rization. With sterilized milks obtained using process temperatures ex ceeding 110 degrees C and equivalent holding times around 40 min a cor relation between the decrease in the content of casein-bound phosphoru s and increasing process temperature was established. Dephosphorylatio n of casein in milk might lead to both a structural change and a reduc ed formation of the phosphopeptides with the consequence that their re gulatory effect as carriers for minerals will be impaired. Compared wi th the mean of the initial milks the measured concentrations of free a mino acids (FAA) showed no clear-cut changes as a function of process temperature and holding time. The variations reflect the different FAA -concentrations in the corresponding initial milks. Hence, the natural content of free amino acids in milk is not significantly influenced b y the processes of heat treatment.