*2.2. Preparation of Solutions*

FG solution was prepared by dissolving citric acid and gelatin in 3 mL of distilled water with citric acid/gelatin/water weight ratio of 0.9:1.0:3.0. The components were mixed together and kept at 50 ◦C under constant stirring (200 rpm) for 40 min. In order to modify the pH of FG solution, an FG+NaOH solution was obtained by dissolving citric acid and gelatin in 2.3 mL of distilled water with a citric acid/gelatin/water weight ratio of 0.9:1.0:2.3 and then adding 0.7 mL of NaOH 5 M. The compositions of FG solutions were optimized on the basis of rheological measurements, taking as a reference a PG solution. PG solution was prepared as previously described [8], in particular, PG was dissolved in a solution of acetic acid and distilled water (60/40 vol% acetic acid/distilled water) at a concentration of 30% (w/v). The obtained solution was stirred at 50 ◦C for 60 min. The pH of the solutions was measured by a calibrated pH meter (XS Instrument pH7, Carpi, Italy). In this work, the pH of the FG solution was 1.8, while the pH of FG+NaOH solution was 3.7.
