The final PVA/chitosan hydrogel (TTI hydrogel) was prepared with
a casting technique at a PVA/chitosan ratio of 3:7 (v/v), with
incorporation of anthocyanin extract. The final concentration of
anthocyanin extract in the filmwas established as 25% of the total
volume of the mixture of hydrogels. A 1.5% solution of sodium
tripolyphosphate (Na5P3O10) 0.1% (w/v) relative to the total volume
of the mixture was added to the final hydrogel in order to
promote cross-linking. The final pH of the hydrogel blend was
adjusted to 6.1 with NaOH (1.0 mol/L), with a colour ranging from
purple to blue. The hydrogel was cast (70 mL) in Petri dishes
(150 mm diameter) and then the plates were placed in an oven for
48 h at a temperature of 35 C to remove the solvent, resulting in
the final TTI films.