Surface Topography of Heat-Set Whey Protein Gels: Effects of Added Salt and Xanthan Gum - Food Colloids: Self-Assembly and Material Science - page 481

Figure 6 Topographic CLSM images of protein distribution at the surface of heat-set
whey protein gels containing different amounts of xanthan: (a) none, (b) 0.05
wt%, and (c) 0.25 wt%. The scales for the x- and y-coordinates are 0-150 m m
and 0-75 m m for all three images. The scales for the z-coordinates are (a) 0-
22.5 m m, (b) 0-20 m m, and (c) 0-15 m m
represent surface water. In contrast, the gel containing 0.05 % xanthan
appeared smooth and almost fully covered by a layer of polymeric material
(Figure 8(b)), with no observable holes across the whole surface. This picture is
consistent with the one shown by CLSM in Figure 7(c). It seems reasonable to
believe, therefore, that a very thin layer of xanthan covers the outer surface of
the heat-set WPI gel. This polysaccharide layer closely 'seals off' the surface and
so makes the biopolymer gel surface much smoother. We should point out that
the presence of such a low xanthan content has no significant effect on the bulk
microstructure of heat-set whey protein gels. That is, ESEM images indicated 12
little difference between the microstructures of a bulk gel without added
polysaccharide and a bulk gel containing 0.05 wt% xanthan.
The effects of xanthan on heat-set WPI gels have been previously reported in
terms of the mechanical properties and the microstructure of the bulk gel state.
Byrant and McClements 13 showed that, in the presence of salt, mixtures of
xanthan + heat-denatured whey proteins are thermodynamically incompatible,