Colour measurement
CIEL⁎a⁎b⁎ colour parameters were measured in a Minolta
colorimeter (Minolta, Model CM-3600d, United Kingdom) controlled
by a computer that calculated colour from the reflectance spectrum.
Sampleswere placed in petri dishes and filled to the top. The petri dish
was placed directly on the colorimeter sensor (3.5 cm in diameter)
and measured; three measurements were taken per treatment per
day. The instrument was calibrated using a white tile (L⁎=93.97,
a⁎=−0.88 and b⁎=1.21) as standard. The L⁎ parameter (lightness
index scale) ranges from 0 (black) to 100 (white). The a⁎ parameter
indicates the degree of red (+a) or green (−a⁎) colour and the b⁎
parameter measures the degree of yellow (+b) or blue (−b⁎) colour.
The CIEL⁎a⁎b⁎ parameters were converted to Hue (arctan b⁎/a⁎),
Chroma (a2+b2)°. The results were expressed in accordance with the
CIELAB system with reference to illuminant D65 and with a visual
angle of 10°.