3. Results and discussion
3.1. Spectroscopic analyses of dyes
The visible spectrum (A) of the aqueous extract of the prickly
pear is shown in Fig. 2. Two peaks corresponding to (i) indicaxanthin
– 475 nm and (ii) betanin – 538 nm have been obtained (José
et al., 2001). The chromatogram (B) analysis is shown in Fig. 2. As
can be seen, two major peaks appear, with peak 1 corresponding
to indicaxanthin, and peak 2 corresponds to betanin.
3.2. Stability of betalains
The influence of temperature on pigment stability was determined
in the extracts obtained from orange-yellow fruits of O.
ficus-indica. When the orange extracts containing the betalains pigments
were heated, the orange colour gradually disappeared. The
absorbance at 538 nm diminished proportionally with the duration
of the heat treatment, at the same time, the absorbance at 475 nm
decrease slightly (Fig. 3).
The quantitative data referring to betanin and indicaxanthin
losses during heating (Table 1) reveal that the first pigment is more
sensitive to temperature than the second one, indeed, treatment
at 90 ◦C for 120 min causing a loss of almost 90% of initial value of
betanin and just a loss of almost 14% of indicaxanthin (Rosario et al.,
2003).
3.3. Separation
The thermal instability due to the betanin, leading to a degradation
in the extract’s colour, opposes to the reproducibility of dyeing.
Thus, the survey resorts to a chromatographic separation in order
to be able to work with indicaxanthin which is the most constant
component.