2.2.1. Hydrogel Preparation

The hydrogel preparation was carried out by thermally-induced gelation. Hydrogels were fabricated with four different concentrations of TAs: 1.5, 3.0, 6.0, and 12.0 mg per mL which corresponds to the TA/WPI ratios were 0.0375/0.075/0.15/0.30 in the hydrogels; a control sample without the TA addition was also prepared. The required amount of TAs was added to the initial solution consisting of 40 mg per mL WPI [23]. All WPI hydrogels were prepared from a solution at pH 7.0. The protein–polyphenol solutions were left in the refrigerator overnight to remove excess air bubbles present. The solutions were transferred to plastic Petri dishes. Gelation was carried out at 90 ◦C for 30 min in an oven. Each cm2 of the Petri dish surface area was occupied by 0.31 mL hydrogel. The resulting hydrogels were then transferred to glass Petri dishes for further autoclaving at 121 ◦C for 15 min before any further characterization.
