2.5.2. Quantification of red pigments
Test solution of pigment samples was determined by spectrophotometry. The details were as follows: the
amount of 0.1 g samples was dissolved and diluted into
100 mL with acetone as a stock solution. Then the stock solution
was diluted into an appropriate concentration with acetone and the
absorbance of the diluted solution was measured against acetone at
460 nm by a spectrophotometer. The content
of red pigments was expressed as the total content of carotenoids
using b-carotene equivalents in mg per g pericarp.
Standard solution was prepared as follows: An amount of 5.6 mg
of b-carotene was accurately weighed and dissolved in 50 mL
acetone. The standard stock solution was diluted with acetone to
appropriate concentrations for the construction of calibration
curves.
For determining the content of red colorant in FRP, the pericarp
after removal of seed and stalk were extracted with acetone until
the color was exhausted. The combined extracts were evaporated
to remove acetone and water under reduced pressure
with a rotary evaporator at 45 C. A residual cream was obtained.
Then it was dissolved with acetone into a determinate volume for
absorbance determination.