Chemistry Reference
In-Depth Information
Figure 11.13.
Distribution of T
2
relaxation times estimated by distributed exponential fitting
of low-field nuclear magnetic resonance relaxation curves obtained on acidified milk drinks
(AMDs) at 58C. The AMDs vary with respect to the combination of pectin concentration (0.0,
0.1, 0.3 and 0.5%) and protein type (skim milk powder (SMP) or SMP with added whey protein
concentrate (SMP/WPC)). Each distribution is a mean of six measurements (Salomonsen et al.,
2007).
As illustrated in Table 11.1, voluminosity (V
e
) (or intrinsic viscosity [
])
varies with the nature of milk protein, temperature and physico-chemical
characteristics of the dispersing medium. For casein monomers, the looser the
conformation, the higher the [
]; see, e.g.
-casein. Structure-loosening with
guanidine chlorohydrate also induces an increase in [
]. On the contrary,
despite a very hydrophilic surface,
-lactoglobulin and
-lactalbumin show
low [
] values because of their compact structure. For casein micelles, high V
e
values (up to 10 ml/g and above) are attributed to water entrapped within
loose aggregates and to the ''hairy'' surface layer composed of the hydrophilic
-casein. Renneting skim milk, before increasing [
] through aggregation of
micelles, is thought to reduce it through the (part) removal of the ''hairy''
layer, as a consequence of the splitting off of the glycomacropeptide from
-casein (Walstra, 1979).
