You may have heard that farmed salmon is injected with dye to get its characteristic 'salmon' colour. That is not true, or at least not in Australia. But the truth is perhaps even worse. 

Astaxanthin (pronounced "ass-tuh-ZAN-thin") is a carotenoid pigment that occurs naturally in krill, crayfish, prawns, and many other marine organisms. It is indeed a dye that gives salmon flesh its 'salmon' colour. But it is not injected. In nature, wild salmon get astaxanthin from the food they eat. Farmed salmon also get astaxanthin from the food they eat: however, this astaxanthin is artificial and made from petrochemicals [1, 2]. 

 

Where does astaxanthin come from? 

Currently, commercial astaxanthin comes from four main sources: processing waste from the shells of crustaceans like krill and shrimp, a type of microalgae called Haematococcus pluvialis, a type of yeast called Phaffia rhodozyma, and the synthethetic form. The latter, the petrochemical one, dominates with about 95% of the market share for aquaculture [3]. The Tasmanian salmon industry refers to this synthetic astaxanthin as "nature identical" [4]. But it is not identical. And it is unnatural. And it is not considered by regulatory bodies to be safe for human consumption. 

We are not being mean-spirited when we say the two forms are not identical. It's not just that they are derived from different sources, the natural form through the food chain and the artificial one from petrochemicals. They are also literally not identical. According to an archived website called The Salmon Files, "Like many organic compounds, astaxanthin occurs in several isomers, sharing the same molecular formula but differing in the geometric arrangement of atoms (including mirror-image "right" and "left-hand" forms and an intermediate symmetrical isomer). In addition, astaxanthin molecules may be "free" or "esterized" (the latter bound to one or two fatty acids). Natural sources tend to contain a mixture of isomers in free, monoester, and diester form, while synthetic astaxanthin consists entirely of free molecules" [5]. It is important to note that isomers are similar but not identical, and they cannot be superimposed upon one another -- they are, in the most literal sense of the word, different [6]. These subtleties of isomers and esters may sound small, but in chemistry they can make the difference between something that is safe to consume, something that is toxic, and something that changes the cells in our body to become cancerous. 

 

Value of astaxanthin

These days, astaxanthin is big business and growing rapidly. In 2000, the annual global market was estimated at US$200 million [3]. By 2010, it was valued at US$283 million, and by 2019 it had shot up to US$584 million; it is expected to reach more than US$2 billion by 2030 [7]. 

Discerning consumers want salmon-coloured salmon, and would likely baulk at bland grey salmon (even though it would be the healthier form). It's kind of like the old story about organic apples: most consumers would reel at the thought of choosing an apple with a worm hole, but that's the healthier one because it lacked the pesticides to repel the worm (and you can chop away the bit with the worm, but you can't chop away the poisons). 

Astaxanthin is a colorant classified as a 'sensory additive', and as such, it is not essential [8]. Don't let the 'not essential' part  fool you, consumer expectations are worth big bucks. Without the addition of artificial astaxanthin, salmon flesh would be a bland pale grey rather than 'salmon coloured'. It wouldn't look right to consumers, that is, it wouldn't match our expectations of what salmon should look like. In fact, market research has shown that consumers prefer well-coloured salmon, equating redder tones with freshness, better flavour, higher quality, and higher price, even though colour does not impact on these characteristics [9]. Salmon farmers order feed according to their desired colour outcome using what's known as a SalmoFan [10], akin to choosing your bathroom colour using paint chips. For example, consumers tested from Seattle and Boston preferred SalmoFan shade #33 by a 2:1 margin, according to industry research [9]. Getting this wrong has consequences. So much so, in fact, that in 2016, Huon Aquaculture stopped paying its feed supplier, Ridley, because, allegedly, the shade wasn't quite right; Ridley sued and won a $16.6 million judgment [11, 12]. 

Besides being a pigment, astaxanthin is a potent antioxidant, or a substance that can protect our cells from oxidation. Oxidation is a decay process inside our body that is conceptually similar to the rusting of unprotected metal pipes or the browning of a cut apple [13]. In vitro studies comparing the antioxident activity in synthetic astaxanthin (S-AX) and natural astaxanthin (N-AX) made from unicellular microalgae found startling results. The N-AX was more than 50 times stronger in singlet oxygen quenching and about 20 times stronger in free radical elimination than S-AX [2]. 
 

Why don't salmon farmers use natural astaxanthin? 

It might seem like using artificial astaxanthin would be a more sustainable option than depleting wild stocks of krill and other crustaceans in order to harvest it. But if that's such an obvious answer, why is the artificial stuff so contentious? And if the fake stuff is so bad, why aren't salmon producers using the natural stuff?  

1. Cost — According to a 2016 study, the market value of astaxanthin typically varies from US$2500-7000/kilogram, with the artificial form involving lower production costs (around US$1000/kg) [14]. Indeed, even though the actual amount of astaxanthin in a salmon fillet is very small, it is the single most expensive component in the feed, accounting for up to 20% of the cost [15]. The artificial stuff is cheaper, simple as that. 

2. Cancer concerns ignored — Currently, the market for natural astaxanthin as a nutraceutical is booming. People are willing to pay big bucks for products that claim a range of health benefits including prevention of cancer and heart disease, immune system boosting, and resistance to ulcers and cataracts [16, 17]. People and regulators are still twitchy, however, about synthetic astaxanthin being made from petrochemicals, because it may contain residual solvents and chemical reagents [1, 17]. Three studies on rodents offer mixed perspectives, with one study on rats finding "no tumorigenic effects, neither benign nor malignant, even at high doses" [17], while another study on rats and one on mice, did find an increase in tumors at high doses [17, 18]. Experts disagree about the implications, with some concluding that these heightened tumors are unlikely to affect humans [18], while others argue that more studies are required before synthetic astaxanthin can be safely used for humans [2, 17]. 

3. Consumer safety — According to a 2013 review, synthetic astaxanthin "has never been demonstrated to be safe for use as a human nutraceutical supplement and has not been tested for health benefits in humans" [2]. Thus, artificial  astaxanthin is not approved for human consumption, only for animal consumption. So presumably, the logic goes something like this: "can't use the cheap artificial stuff in people's food, might as well use it in fish feed (and enjoy a higher profit margin)". On the one hand, it might seem practical, or even desirable, to use the cheap, plentiful artificial stuff as a fish supplement and leave the more limited natural stuff for humans, but on the other hand, how do we feel about eating something that contains ingredients not fit for human consumption? 

 

Is artificial astaxanthin safe?

Given the above considerations, it seems reasonable to ask the question, Is artificial astaxanthin safe? If it is not permitted as a safe supplement for humans, should we be suspicious about its safety as a supplement for our food? We already know that petrochemicals can have some undesirable side effects, so it would seem that our starting position should be to prohibit it until it is proven safe, rather than to approve it until people become unwell. 

Where are the human clinical trials? Where can we find the long-term safety parameters and recommended intake guidelines? It is frankly almost inconceivable in this day and age that a petrochemical product could be fed to our food without safety testing on humans. 

 

REFERENCES

[Click here to go to Astaxanthin References]

Image Atlantic Salmon © L. Gershwin