2.8. Color measurement
Surface color of the cut apples was directly measured with an XRite
SP62 (Cologne, Germany) colorimeter. Each measurement was
taken at 3 locations of 4 apple slices (n ¼ 8) and calibrated using a
standard white reflector and black plate. Lightness is reported as L*;
the lightness value for perfect white is 100, while L* ¼ 0 corresponds
to black. The a* value indicates chromaticity on a green ()
to red (þ) axis and b* indicates chromaticity on a blue () to yellow
(þ) axis. The hue angle (h) value was calculated using following
equation.