Oil colour was measured with a Minolta chromometer CR-400
(Minolta, Tokyo, Japan). Oil was placed in a Minolta standard
cuvette and measurements were recorded in Hunter units of L [L:
0 (black), L: 100 (white)], a (+a: red, a: green), and b (+b: yellow,
b: blue). The chroma value was calculated according to the equation:
C = (a2 + b2)1/2.