3.3. Fracture properties
The fracture properties were sensitive to changes occurring in
microstructure caused by k-carrageenan addition (Figs. 4 and 5).
The microstructure of WPI gels shifted from stranded to particulate
when NaCl concentrations increased from 50 to 250 mM. The two
stranded gels (50e100 mM) had different fracture properties.
Increasing NaCl concentration from 50 to 100 mM caused an
increase in fracture stress and decrease in fracture strain. The
fracture stress values of particulate gels (250 mM NaCl) were
similar to stranded gels (50 mM NaCl) but fracture strain values
were lower. This coincides with previous investigations from our
lab (Kuhn & Foegeding, 1991; McGuffey & Foegeding, 2001) and
others (Barbut, 1995; Mulvihill & Kinsella, 1988). Overall, the fracture
stress of whey protein gels ranged from 29 to 44 kPa, while
fracture strain varied from 0.9 to 1.8, by moving from stranded to
particulate structure (Figs. 4 and 5).