2.4.3. Color Measurement

Sample color was measured on the CIELAB L\*a\*b\* chromatic space with a Minolta CR-300 colorimeter (Minolta, Osaka, Japan) with standard illuminant D65 and a visual angle of 2◦. Tri-stimulus color coordinates (CIELAB system) were used to measure the degree of lightness (L\*) which ranges from 0 (black) to 100 (white), redness (a) ranging from −60 (green) to +60 (red) and yellowness (b) ranging from blue (−60) to yellow (+60). The instrument was initially calibrated using a white ceramic tile (L\*97.21; a\* 0.13; b\* 2.00). The measurement was performed by placing a piece of lettuce directly under the sensor and at least 30 measurements were done by treatment and day of evaluation, covering three different leaves coloration picked by naked eye selection (dark green, median green and light green).
