the color of butterfly pea solution depends on the
change in equilibrium of four anthocyanin species
according to the prevailing pH [14]. At low pH,
anthocyanins present as the red flavylium cation.
Increasing the pH results in decreasing the color intensity
and the concentration of the flavylium cation, as it is
transformed into blue quinonoidal base or colourless
carbinol pseudobase, and into yellow chalcone species
[14]. The effect of pH on the color of butterfly pea
solution was confirmed by spectrophotometric analysis.
Scan spectrum showed different λmax values at various
pH as described in Table 2.
Color stability of butterfly pea aqueous color solution
Thermal stability
Temperature affected the color stability of the
extract solution at various pH. The butterfly pea solution
stored at 4 ÌC showed higher color stability than the
solution stored at 40 ÌC (Figure 1, Table 3). The effect of
rising temperature on color loss was more predominant
on neutral solution (pH 7) than the acidic and alkaline
solutions (pH 4 and 10, respectively); color remaining of
90% was observed in 15 days at pH 4 and 10 while it
was in 1 day at pH 7. Increasing temperature induces
the loss of glycosyl moieties of anthocyanin by the
hydrolysis of glycosidic bond [15]. The resulting aglycones
are less stable and lead to the loss of anthocyanin
color. In general, anthocyanins are more stable in the
acidic medium at low pH than in the alkaline medium
at high pH. However, several studies demonstrated
that some anthocyanins showed an improvement of
color stability in the alkaline region around pH 8-9
[16, 17]. The color extract was the most stable in
acidic solution at 4 ÌC and the least stable in neutral
solution at 40 ÌC.