The astaxanthin content in the powders was determined by
modifying the method of Ax et al. (2003). Extract (0.1 g) obtained
from core material was dissolved in 5 mL of acetone, followed by
5 mL of n-hexane and 5 mL of 1 M NaCl solutions. The mixture
was vortexed and the organic phase (upper layer) was transferred
to a test tube. The organic phase was then washed with 5 mL MilliQ
water and transferred to a 25 mL volumetric flask making up to
25 mL with hexane. The astaxanthin concentration was determined
at 478 nm using a UV–VIS spectrophotometer (Shimadzu
UVmini 1240, Japan), against a hexane blank. Determination of
astaxanthin content was conducted using an astaxanthin calibration
curve at the same absorbance.