Water in Dairy Products - Advanced Dairy Chemistry - page 495

Figure 11.18. Crystallization rate of amorphous lactose at three water levels.
The lines are the fitting of data to the semi-empirical Lauritsen-Hoffman model (Kedward et al.,
2000).

formulation (see Buera et al., 2005, for a review). -Lactoglobulin was shown
to retard the crystallization of lactose in whey powder, when co-lyophilized.
This effect was ascribed to non-covalent or covalent interactions between
lactose and -lactoglobulin resulting in modifications of the water sorption
behaviour (Thomas et al., 2004).

11.5.5.3. Non-enzymatic Browning and Other Chemical Reactions

In our earlier review (LeMeste et al., 2002), the provisional conclusion
was that the temperature of glass transition does not constitute an absolute
stability threshold and that, above this temperature, the reaction kinetics do
not obey WLF kinetics. Almost all of the quoted studies reported finite
reaction rates in glassy products. The reaction rate increased with the differ-
ence (T-T g ). However, when the variation of T g was induced by changes in
water content, the expected single relationship between the rate and (T-T g )
was not observed. The reaction rate evolution with temperature was most
often described as uniform, of Arrhenius type, even within the glass transition
temperature range. The apparent activation energy remained low, even at T >
T g , in the range 100-150 kJ/mol. These values are much smaller than the
activation energies commonly observed for dynamical properties in the glass