Chemicals add shelf life and water weight to shrimp and scallops, while CO gas is used to redden tuna artificially
by Craig Weatherby
This week we received a question that comes up fairly often, concerning an additive commonly added to ham and shellfish.
We thought our readers might be interested in the query and our answer, since the chemical in question is frequently added to shrimp and scallops.
And it gives us the opportunity to address another, little-known practice, whereby sellers of fresh and frozen tuna use a greenhouse gas to keep the fish artificially colorful.
Thank you so very much for providing the quality products and the quality service you provide. I have never found anything to compare with your fish and the variety of what you offer all to be found in one place. Many kudos to you.
I would also like to inquire a little concerning an article I read in [a major food retailer's] magazine. They are claiming not to use STP sodium tripolyphosphate in their tuna and scallops.
Can you tell me a little about STP and whether or not Vital Choice uses STP in its products?
Our answer (edited for publication)
Thanks for your kind comments and your excellent question.
Manufacturers and retailers use STP to extend the shelf life of meats and thawed shrimp and scallops and/or to retain moisture in meats and thawed shellfish, which increases profits.
We of course do not use STP or any other additives in our scallops, crab, or shrimp, or in any of our products.
It is often abused (added in amounts exceeding legal limits) to add water weight to shrimp and scallops.
The addition of STP to shellfish can make the meat tough or rubbery, and produce a tart, metallic, chemical flavor. If the product feels glassy or overly slimy in the raw, thawed state, it's probably been soaked in STP too long.
STP is not considered unsafe in the amounts ingested through consumption of treated shellfish, but the following information, which comes from one laboratory's federally mandated material safety data sheet reveals that STP is not entirely innocuous:
Potential Acute Health Effects:
Very hazardous in case of eye contact (irritant). Hazardous in case of skin contact (irritant), of ingestion, of inhalation. Slightly hazardous in case of skin contact (sensitizer, permeator).
Inflammation of the eye is characterized by redness, watering, and itching.
Potential Chronic Health Effects:
Carcinogenic Effects: Not available.
Mutagenic Effects: Not available. [A mutagen is a substance that can damage or change the genetic information (DNA) of an organism.]
Teratogenic Effects: Not available. [A teratogen is a substance that can disturb the growth and development of an embryo or fetus.]
Developmental toxicity: Not available.
The substance is toxic to lungs. Repeated or prolonged exposure to the substance can produce organ damage.
General Product Information
This product is considered hazardous under 29 CFR 1910.1200 (Hazard Communication).
Thanks again for your question, and your compliments!
Raising a red flag on colorful Tuna: Don’t be fooled by CO-gassed fish
If the tuna you see in a supermarket or sushi bar is a bright watermelon red, its color's likely been enhanced with carbon monoxide (CO) gas.
Unbeknownst to most consumers, many wholesale Tuna suppliers expose fresh Tuna to carbon monoxide (CO), which serves to preserve the fishes’ natural red color.
Wholesalers usually CO-treat flash-frozen Tuna at the request of retailers concerned about their customers' probable misperceptions concerning the meaning of color of Tuna meat.
We've never sold CO-treated Tuna because it constitutes deception, however innocuous its health effects... unless this color charade is exploited to mask the sorry state of near-spoiled supermarket fish.
The light pink-to-red/purple color of freshly caught Tuna can change within a few hours or days to a less-appealing brown: a process accelerated by cutting the meat in pieces. Retailers and restaurateurs are acutely aware that consumers will reject paler, browner Tuna, and pay more for vibrantly colorful cuts.
CO gas can also be used to deepen the Tuna’s natural red color, to raise consumer’s perception of its quality and freshness.
In reality, color reveals little about the age or wholesomeness of a piece of Tuna, because the natural color change from red to tan occurs long before the fish has begun to deteriorate.
There nothing unhealthful about CO-treated Tuna and the FDA has good reason to find CO-exposed tuna, per se, safe.
However, CO-treated Tuna is sometimes used to (illegally) conceal a spoiling piece of fish.
Research shows that spoilage can continue in CO-treated fish whose color remains bright red. Accordingly, several countries prohibit CO-treatment of fish. Japan outlawed it in 1997, while the European Union began to enforce a ban 2004.
The FDA requires that seafood exposed to CO be labeled accordingly, but this rule is rarely honored and is hard to enforce, as it is not easy to tell when tuna has been artificially reddened.
How does CO gas keep Tuna red?
Tuna flesh contains myoglobin, a pigmented protein that stores oxygen. Myoglobin changes color, depending in part on how much oxygen is available to it.
The dark, purplish red color of freshly cut Tuna comes from deoxymyoglobin, which – once exposed to air – changes first to bright red-hued oxymyoglobin and then to brown-hued metmyoglobin.
CO gas preserves Tuna’s fresh-caught red color by replacing the oxygen in the oxymyoglobin molecules, thereby converting them into a stable red compound called carboxymyoglobin.
Tuna supplier can use bottled CO gas, but more expose Tuna to filtered wood smoke, which contains carbon monoxide. (Fish treated with filtered smoke may not be labeled “smoked,” because they lack significant smoke flavor.)
The amount of myoglobin in a Tuna’s muscle determines its color, and the amount of myoglobin is a function of a Tuna’s age (size), physical activity and species: the older the fish, the redder its flesh.
Albacore Tuna is naturally lower in myoglobin, compared with the Bluefin and Yellowfin Tuna that predominate in most supermarket seafood cases and in sushi bars.
Thus, Bluefin and Yellowfin tuna usually appear much redder than Albacore, if the pieces are displayed very soon after exposure to air… or if they’ve been exposed to CO gas.
We pick only young, small, Albacore, so our portions – which are cut and flash-frozen within hours of harvest – usually show little red color.
In fact, the white/tan color of our Albacore Tuna is one sign that you are getting a small, young fish that is, as a consequence, extremely low in mercury compared with most fresh-frozen and canned Tuna on the market. (Click here for a comparative chart showing the average mercury content of standard Tuna and Vital Choice Tuna.)