Microalgae: A Renewable Source of Bioproducts - Food and Industrial Bioproducts and Bioprocessing - page 228

9.8.5 Pigments
Microalgae are excellent sources of natural carotenoid and chlorophyll pigments. Over 600
carotenoids are now known and many of these are produced by microalgae. Sophisticated
high performance liquid chromatography (HPLC) methods using reverse-phase C 18 columns
to separate both carotenoids and chlorophylls in a single analysis have been developed
(Wright et al ., 1991; Van Heukelem and Thomas, 2001), which has enabled extensive
databases of the characteristic pigment compositions of the different algal classes to become
available (Wright and Jeffrey, 1987 , 2005 ; Jeffrey et al ., 1997 ).
A distinction is made between primary and secondary carotenoids. Primary xanthophylls
(i.e. oxygenated carotenoids) are structural and functional components of the photosynthetic
apparatus of the cell, and hence essential for cellular survival. Secondary xanthophylls are
those that microalgae produce in large quantities after exposure to specific environmental
stimuli (carotenogenesis), such as high light, oxygenated species and so on (Jin et al ., 2003 ).
Plate 9.2 gives examples of pigment profiles of different microalgal classes. Within one
class there can be compositional variations between genera, species and even strains; this
needs to be considered when selecting strains for pigment production. However, as a
preliminary screening device the algal class is generally a good guide to which pigments
will predominate.
Aquaculture-reared salmonids require pigment added to their diet to attain commercially
desirable pink-coloured flesh. Synthetic pigments have traditionally been used but natural
sources of astaxanthin are now available. For example, the green microalga Haematococcus
pluvialis has a particularly high content of astaxanthin (1-3% of the dry weight) and is now
grown commercially as a carotenoid source for use in aquaculture, in poultry feed and as an
antioxidant (Lorenz and Cysewski, 2000). There is a striking difference in pigment
composition in Haematococcus between the different life stages of vegetative cells and the
resting stage: vegetative cells can contain significant amounts of lutein and are low in
astaxanthin, while the aplanospores contain high levels of astaxanthin. Table 9.2 shows a
full pigment composition and Jeffrey and Egeland (2009) provide more information on
regulation of pigment synthesis.

Table 9.2 Pigment composition of vegetative cells and aplanospores
of Haematococcus (Harker and Young, 1995).

Pigment Vegtative cells Aplanospores

(%) (%)

Neoxanthin 13.0 ND

Violaxanthin 14.5 ND

Lutein-5,6-epoxide 5.2 ND

Lutein 53.8 1.0

β ‚ β -Carotene 13.5 3.0

Canthaxanthin ND 2.0

Adonirubin ND 2.0

Echinenone ND 3.0

Astaxanthin (unesterified) ND 1.0

Astaxanthin (monoester) ND 49.0

Astaxanthin (diester) ND 39.0

ND = Not Detected