What Forms of Astaxanthin are Found in Nature?

Form and level of deposition of astaxanthin differ between tissues and species. Esterified astaxanthin predominates in the skin, teguments, and eggs, while free astaxanthin is the main form in the flesh, serum and other internal organs of salmon.2 In shrimp, esterified astaxanthin predominates, except in the ovaries and eggs.17,18 In red seabream, mostly esterified astaxanthin is found in the skin.14,15 The more stable esterified form is believed to be an adaptive feature to be able to store astaxanthin in tissues without excessive oxidation.1 Esterified astaxanthin is the main form found in Haematococcus pluvialis.

Although they have the same chemical composition, 3 main spatial configurations or enantiomers of the astaxanthin molecule can be found in nature. They are the 3S-3’S, 3R-3’S, and 3R-3’R isomers, characterized by the position of the two hydroxyl groups on the molecule. A recent study by FDA concluded that the 3S-3’S is the main form found in wild Pacific and Atlantic salmon species.16 This is the same form as the one found in Haematococcus pluvialis. This same study showed that farmed salmon could be easily distinguished from the wild salmon because the farmed salmon are fed synthetic astaxanthin. Synthetic astaxanthin contains primarily the 3R-3’S isomer and are unable to convert it to the more common and natural 3S-3’S form. Farmed salmon should be fed a diet containing natural astaxanthin to achieve the same astaxanthin profile as their wild counterparts.

Table 1. Main forms of astaxanthin in tissues of important aquaculture species

Tissues

Skin

Flesh

Digestive

gland

Ovaries

Serum

Eggs

Species

Salmonids2

Shrimp17,18

Red Seabream14,15

Esterified

Free

Esterified

N.A.

Free

N.A.

Free

N.A.

Free

N.A.

Esterified

Free

N.A.

N.A. : not available

Table 2. Form and level of astaxanthin in selected important
Aquaculture species and potential astaxanthin sources

Aquaculture species	Content (mg/kg)	Astaxanthin Free/esterified	Main isomer	Ref.
Sockeye salmon	26-37	Free,esterified**	3S-3’S	2,16
Coho salmon	9-21	Free,esterified**	3S-3’S	2,16
Chum salmon	3-8	Free,esterified**	3S-3’S	2,16
Chinook salmon	8-9	Free,esterified**	3S-3’S	2,16
Pink salmon	4-6	Free,esterified**	3S-3’S	2,16
Atlantic salmon	3-11	Free,esterified**	3S-3’S	2,16
Rainbow trout	1-3	Free,esterified**	3S-3’S	2
salmon eggs	0-14	esterified***	N.A.	19,20
Red seabream	2-14	esterified***	N.A.	14,15
Red seabream eggs	3-8	N.A.	N.A.	20
Peneaus monodon	10-150	Esterified,free**	3S-3’S	18
Lobster		Esterified,free**	N.A.*	21,22

Astaxanthin sources
Copepods	39-84	esterified***	N.A.*	2
Krill	46-130	esterified***	3R-3’R	2
Krill oil	727	esterified***	3R-3’R	2
Crayfish meal	137	esterified***	N.A.*	2
Artic shrimp	1160	esterified***	3S-3’S	2
Yeast (Pfaffia r.)	30-800	esterified***	3R-3’R	2
Synthetic astaxanthin	80,000	free	3R-3’S	2
Haematococcus pluvialis	10,000-30,000	esterified***	3S-3’S	23

* Crustaceans are believed to have mostly the 3S-3’S form, Krill might be the exception.
** depending on tissues, free or esterified astaxanthin may be found
*** also contain a small proportion of free astaxanthin
N.A.: not available

References