WPI and SPI were dissolved in double deionized water at 23 °C by
using a stirring hotplate (Fisher Scientific) to form 1 wt.% and 2 wt.%
protein solutions. For the heated WPI solutions, the WPI was first
dissolved in water at 23 °C and then heated in a water bath (Fisher
Water Bath, Fisher Scientific) to 80 °C for 30 min. The gelatin needed
to be solubilized in 60 °C double deionized water. The 1 wt.% and
2wt.% solubilized gelatin solutions were then heated to 80 °C in
50 mL polypropylene disposable centrifuge tubes (Fisher Scientific)
and held at that temperature for 30 min in a similar fashion as the
heated WPI solutions. Both the heated WPI and gelatin solutions
were cooled to 23 °C before the alginate was added. Alginate was
mixed by hand into all of the protein solutions to obtain 5wt.%
alginate in each of the solutions (concentration was determined by
preliminary experiments). The total hand mixing time was 15 min.
A control sample of 5wt.% alginate was also made. In order to remove
some of the air incorporated into the alginate–protein solutions
during mixing, each of the solutions was degassed by using a Multivac
vacuum packager (Multivac Canada Inc., Woodbridge, ON, Canada)
at 94 kPa for 25 s then again at 94 kPa for 50 s and 75 s (settings 4,
6 and 8 respectively). The solutions were then allowed to hydrate
for a minimum of 2 h at 23 °C.