Purification of trans-astaxanthin from a high-yielding astaxanthin ester-producing strain of the microalga Haematococcus pluvialis

The purification method including extraction, saponification, and separation was established for preparing free trans-astaxanthin from a high-yielding astaxanthin ester-producing strain of the microalga Haematococcus pluvialis which contained 3.67% trans-astaxanthins and 1.35% cis-astaxanthins of the dry cells. Low temperature (5°C) was chosen to minimize the degradation of astaxanthins during saponification, and 94.4% free trans-astaxanthin was obtained from trans-astaxanthin esters after 12 h of saponification. With this method, 32.2 mg trans-astaxanthin was obtained from 1 g dry algal cells. In addition, a new gradient reversed-phase HPLC method, suited for the quick analysis of free astaxanthins and astaxanthin esters in the unsaponified and saponified pigment extracts from the high-yielding astaxanthin ester-producing strain of the microalga Haematococcus pluvialis, was developed and applied to the determination of astaxanthin contents during the processes of extraction, saponification, and purification.