2.9 Stability of the Colorants
The investigation of the stability of the colorants and their resistance to degradation by temperature, as well as the pH value in the color of the colorants and salt concentrations was carried out as described [22] with modifications, whereby the colorants (0.1 mg/mL of DMSO) were incubated in a water bath for 1 hour at 40 °C, 60 °C, 80 °C, 100 °C or frozen at -20 °C before analysis. In another set of tubes, extracts were adjusted to pH 2, 4, 6, 8, 10 and incubated for 1 hour at room temperature. Test tubes containing the extracts maintained in 0.2%, 0.4%, 0.6%, 0.8% and 1% (v/v) NaCl solutions for 6 h of exposure.
For the investigation of their resistance to photodegradation, the colorants were left in a dark place (and covered with aluminum foil), exposed to white light (distance of 30 cm, 28W Cold White 5000K Tubular Fluorescent Lamp Brand/Manufacturer: Osram, Barueri-SP, Brazil) and ultraviolet light (distance of 30 cm, Ultraviolet Lamp 24W Pl Osram Germicidal Reactor, Barueri-SP, Brazil), for 6 h. Changes in absorbance were determined using a spectrophotometer at the maximum wavelength of the analyzed colorants (λmax).