Vitamin E is a fat-soluble vitamin that plays many important roles in the body, including a key role as an antioxidant. This article by Louisana State University professor Subramaniam Sathivel describes how fish, including cod, assimilate vitamin E through the marine food chain. In addition, Dr. Sathivel explains that the form of vitamin E with the greatest antioxidant activity is the principal component of vitamin E found in marine animals. The gentle and minimal processing techniques used by Green Pasture to extract cod liver oil allow the extracted oil to retain abundant bioactive compounds that include vitamin E and other health-beneficial compounds.
Vitamin E in Cod Liver Oil
By Dr. Subramaniam Sathivel
Vitamin E, an antioxidant nutrient, is synthesized (made) in plants and algae (Whistance and Threlfall, 1970). It is also found in fish and marine animals, but fish do not themselves synthesize vitamin E. This raises an interesting question: How does vitamin E come to be found in fish? Simply put, fish assimilate vitamin E from their diet. The cycle begins with small organisms called zooplankton that consume phytoplankton (microalgae, which can produce vitamin E); the zooplankton then are consumed by small fish, which are eaten by larger fish, and so on.
There are a number of small fishes that eat macroalgae, often called “algae eaters.” These small algae eaters are an integral part of a cod’s food chain. In Alaskan coastal areas, commonly found macroalgae include Phaeophyta (brown algae) species (Fucus distichus, Saccharina latissima, Saccharina groenlandica, and Alaria marginata); Rhodophyta (red algae) species (Porphyra fallax); and Chlorophyta (green algae) species (Ulva lactuca) (Kellogg et al., 2014).
There is another pertinent question related to vitamin E: Do particular species of fish contain a significant amount of vitamin E, and if so, where is that vitamin E stored in the fish? As it happens, coldwater fish such as cod tend to contain more vitamin E than warm water fish. Because vitamin E is fat-soluble, for the most part it is dissolved in the lipids (fat and oils) stored in the liver, which means that when the oil is extracted from the cod liver, vitamin E gets extracted along with the oil. (However, the final concentration of vitamin E in the oil depends on the extraction methods and conditions and on a number of other factors.
Vitamin E is considered an antioxidant because it is able to reduce or prevent lipid oxidation. Plants, algae, and cyanobacteria produce vitamin E in the form of Α-, Β-, Γ-, and Δ-tocopherols and Α-, Β-, Γ-, and Δ-tocotrienols. The Α-form of vitamin E has the greatest antioxidant activity among the tocopherols and tocotrienols, and Α-tocopherol is the principal tocopherol found in marine animals (Syväoja et al., 1985). As already noted, cod fish and other fish cannot synthesize tocopherols directly, but as ocean predators that eat smaller fish (including algae eaters), cod fish are able to assimilate vitamin E and other health-beneficial bioactive compounds such as pigments and polyphenols. Factors such as season, food, size, and age can influence the concentration of tocopherols (Ackman and Cormier, 1967; López et al., 1995), but in general, cod liver oil contains 0.26-0.32 mg Α-tocopherol per gram of lipid (O´Keefe and Ackman, 1986).
Recently, researchers detected in cold-acclimated fish a new marine-derived tocopherol (MDT) that may be capable of providing additional antioxidant and health benefits (Yamamoto et al., 2001). Coldwater Pacific chum salmon (Oncorhynchus keta) and its eggs, sockeye salmon (Oncorhynchus nerka), and Alaska pollock (Gadus chalcogrammus) contain relatively high concentrations of MDT. MDT (like vitamin E) originates from the fish’s diet (Yamamoto et al., 1999). Thus, MDT in the tissues of wild masu salmon (Oncorhynchus masou) is reportedly higher than that found in the tissues of aqua-cultured masu salmon.
Pacific cod (Gadus macrocephalus) is a coldwater fish in which concentrations of 3.1 nmole of MDT per gram of wet muscle tissue have been noted. Although this is a low concentration, it may be sufficient to impart health benefits when consumed. There is little information available on the MDT concentration in cod liver oil. However, because higher concentrations of lipid are stored in a cod’s liver than in its muscle, there is a good possibility that MDT is present in greater concentrations in the oil than the lower levels noted in the flesh. Through adherence to minimal processing techniques to extract cod liver oil, one would expect the extracted oil to contain an abundance of these natural bioactive compounds.
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Subramaniam Sathivel, Ph.D. Professor of Food Processing Engineering
Dr. Sathivel is the Professor of Food Engineer at the School Nutrition and Food Sciences and the Department of Biological and Agricultural Engineering, Louisiana State University Agricultural Center (LSUAC). Before joined LSUAC, Dr. Sathivel worked five years as an Assistant Professor of Seafood Processing and Engineering at the Fishery Industry Technology Center (FITC), University of Alaska Fairbanks, Alaska. He is responsible for the food process engineering laboratory at the LSUAC, where his projects include design and development of an adsorption technology to purify fish oils and fish protein, value added products, edible films and edible coatings. Dr. Sathivel has published 60 refereed articles, two popular articles, five book chapters, and six proceedings. Dr. Sathivel has an equally respectable record of published abstracts and professional presentations, many of which were invited talks at international scientific meetings and conferences.