Changes in Visual Color Attributes
The changes in visual color were evaluated by the CIELab
parameters which can achieve a precise color characterization
and are gaining in popularity as descriptors for use in color
specification by food manufacturers. It can be observed that
thermal processing involves an increase in the lightness (L*),
accompanied by a decrease in the red-green parameter (a*),
particularly in the most thermosensitive extracts, and a slight
increase in the blue-yellow parameter (b*). These effects are
similar to those reported for aqueous anthocyanin extracts [23,
28] and also for betacyanin extracts [20, 31]. As seen in Fig. 4,
plotting the values in the plane a* vs. b* (colorimetric plane)
illustrates how redness decreases during the heating period.
The greater the dispersion of the points among the same series
the more pronounced color degradation. Red cochineal
extracts were the only ones to remain grouped after treatment
for 6 h at 50, 70 or 90 °C, with color differences (ΔE*) of 7.9,
10.1 and 12.2, respectively (Table 2). This, corroborates the
view that red cochineal is the most thermoresistant extract,
while red beet and Opuntia extracts showed a pronounced
degree of degradation even during heating at moderate temperature
(50 °C). The color differences confirmed the greater
thermolability of both betacyanin extracts.