PBS and UHT milk as a function of heating
time at 65, 72, 80 and 90 °C are shown in
Figure 1 and Figure 2, respectively. The
IGF-I concentration decreased with time
and temperature of treatment. In all
temperature-time courses, the denaturation
rate of IGF-I was higher in PBS than in
UHT milk. Table I shows the D- and
Z-values for denaturation of IGF-I. Higher
D-values were found in UHT milk for all
temperatures, compared with PBS. The
Z-values calculated by logarithmic plots of
the D-values versus temperature (Fig. 3)
were 27.12 °C in UHT milk, and 24.41 °C
in PBS. This indicates a higher thermoresistance
of IGF-I in UHT milk than in
PBS over the temperature range studied.
3.2. Reaction order and rate constant