3.4. Held water
Held water represents the fraction of total moisture that is held
by the protein network under a given force. It reflects the moisture
release during mastication (Gwartney et al., 2004). The differences
in the capacity of WPI/k-carrageenan mixed gels to hold the
aqueous phase in their network during centrifugation corresponded
to the differences in the microstructure (Fig. 8). As the
ionic strength increased, the structure of WPI gels moved from
stranded to particulate, accompanied by a decrease in held water. It
was clearly observed from the microscopic images that WPI gels at
50 and 100 mM NaCl had homogenous networks with considerably
low porosity, leading to high water-holding properties. In contrast,
WPI gels at 250 mM NaCl had a micro-phase separated structure
with a coarse network with large pores of enclosed fluid. This
microstructure led to a relatively low water-holding capacity (Table
1). The results from this investigation were consistent with
previous research showing stranded WPI gels have higher waterholding
capacities than particulate WPI gels (Bowland & Foegeding,
1995; McGuffey & Foegeding, 2001; Stading & Hermansson, 1991).