Last Updated July 24, 2019

Below are opinions from Dr. DeLuca and Dr. Sathivel, who are leading scientists in their fields.

Dr. Sathivel’s Response

Dr. Sathivel is an expert in the area of fish oil processing. We have consulted and been taught by him for many years.

Dear Mr. Wetzel,

The Alaskan pollock industry is a multimillion dollar industry. The nutritional quality of pollock fillets is very high and like other fish. Pollock is mainly used for surimi production and for fish sandwiches. It can also be used for producing fish fingers.

Both pollock and cod are from the family Gadidae and genus Gadus. Based on genus classification, oil produced from either pollock or cod livers can be called cod liver oil. In addition, the fatty acid profile of the cod and pollock oils, especially eicosapentaenoic (EPA) and docosahexaenoic (DHA), are similar.

Oil can be extracted from whole fish and/or fish processing byproducts including viscera, heads, skins, frame, and discarded fish. Fish byproducts are obtained from edible fisheries processes such as filleting operations, fish canning, roe fishing, and surimi processing. Menhaden oil is extracted from whole menhaden while salmon, cod, and pollock oils are extracted from their processing byproducts. Salmon oil is extracted from heads, while cod liver oil is extracted from livers of cod and pollock.

Dr. SathivelPlease note that you are using human food grade cod and pollock livers from the Alaska fish processing Industry. The industry collects the livers then pack, and freezes them before they ship it to you. It is similar to how they deal with frozen fish fillets. It indicates that livers should arrive at your facility in good condition. Please note that freezing is one of the best methods to maintain food quality.

Pictures: Frozen cod livers for extracting cod liver oil

Almost all animal fats are recovered by rendering, whereas vegetable oils are obtained by crushing/pressing or solvent extraction or both. In general, rendering can be conducted under a wet or dry condition. Wet rendering is carried out with large amounts of water. The fat cell walls are broken down by steam under pressure until they are partially liquefied and the released fat floats to the surface of the water. Separated fat is removed by skimming or by centrifugal methods. Wet rendering is a universal process and used in most of the fish oil industry.

Fermentation is another method to extract fish oil from fish tissues. During fermentation, fish tissues release fat molecules. It is a slow process. There is a very good possibility that a small quantity of lipase enzyme would naturally be in the tissue. The lipase enzyme and the fermentation process provide conditions that are favorable for producing free fatty acids (FFA) from triglycerides. In general, free fatty acids are susceptible to lipid oxidation. The rancidity values, such as peroxide values (PV), p-Anisidine value, and thiobarbituric acid (TBA), are of prime importance for quality control of edible fats and oils. PV measures primary lipid oxidation products. The p-anisidine value estimates the amount of a- and ß- unsaturated aldehydes (mainly 2-alkenals and 2, 4-dienals), which are secondary oxidation products in fats and oils. The secondary lipid oxidation products are also evaluated by the measurement of malondialdehyde (MDA) reacting with thiobarbituric acid (TBA). PV is good for measuring the total concentration of peroxides and hydroperoxides (primary oxidation products) present in oils at a particular time. In my opinion, PV is not reliable. Over time, primary oxidation products are decayed and formed carbonyl compounds. Rancidity and other objectionable organoleptic flavors in oil are a result of carbonyl compounds. Some consumers may have particular sensitivity to rancid flavors while other consumers may not notice rancid flavors (for example, parmesan cheese). In general, lipid oxidation data (PV), p-Anisidine value, and (TBA) are mainly related to sensory attributes.

Note, however, that the TBA value of your fish oils is less than one, which is well below the acceptable level. This indicates the oil is not oxidized to a significant extent. This may be due to the presence of carotenoid pigments and vitamin E. They are strong antioxidants. These pigments may provide a yellowish to dark reddish and/or dark brown color to the oil. Some fish oil processors remove these pigments using a number of separation techniques that results in much lighter color oil. During the process, vitamins may be removed from the oil.

You have routinely had commercial analytical labs analyze samples of your fish oil. The data obtained did not show trans fatty acids, that is, if trans fatty acids did exist, they were present at a very low level. In general, fish oils may contain very low levels of trans fatty acids.

Low levels of trans fatty acid may naturally present in bovine milk fat (0.6 - 3.9%) (Månsson, 2008), beef meat (3.6%) (Woods & Fearon, 2009), and dairy creams (3.02 to 4.11g/100 g) (Jan et al., 2011). This may be the result of microbial hydrogenation of cis-unsaturated fatty acids in the stomach of ruminant animals (Bauman & Griinari, 2003).

In my opinion, your company produces quality fish oil. Scientifically, you can still call your fish oil cod liver oil but I would like to suggest that you list species specification information on the label to remove any possibility of confusion.

If you have any questions, please let me know.

Subramaniam Sathivel, PhD


Bauman, D. E., & Griinari, J. M. (2003). Nutritional regulation of milk fat synthesis. Annual review of nutrition, 23(1), 203-227.

Jan, M., Filip, S., Polak, T., Hribar, J., & Vidrih, R. (2011). Quantitative comparison of the fatty acid composition of dairy and artificial creams and their nutritional value in the human diet. Milchwissenschaft-Milk Science International, 66(2), 186.

Månsson, H. L. (2008). Fatty acids in bovine milk fat. Food Nutrition Research, 52(6), 1e3.

Woods, V. B., & Fearon, A. M. (2009). Dietary sources of unsaturated fatty acids for animals and their transfer into meat, milk and eggs: A review. Livestock Science, 126(1-3), 1-20.

About Dr. Sathivel

Dr. SathivelDr. 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.

Dr. DeLuca’s Response

Dr. DeLuca is a well-known scientist in the field of Vitamins (see bio). He has taught us and coordinated the rat bioassays to better understand the vitamins within our products.

Let me just say the following. Yes, the assays we carried our are bioassays; they are carried out in Vitamin D deficient rats which means they have no Vitamin D in them and they develop low blood calcium and the only way you can raise their calcium is to give them Vitamin D and we use the elevation of serum calcium in response to the samples and that is something that absorbs in the UV in that range.  The same is true with spectrophotometric measurements. They are not as reliable as bioassay.  Bioassay is the only reliable measure of Vitamin D unless you go all the way through to isolation and identification of the structure by mass spectrometry or some other physical measurement other than ultraviolet absorption. So, we are very confident that our bioassay gave the real results, and we believe that you can be very easily mislead by using just UV or just HPLC to try to measure Vitamin D content of oils or just HPLC to try to measure Vitamin D content of oils or other such supplements. You can't fool a rat.  You have to take into account that it takes significant time and expense; this is why it is not used.

About Dr. DeLuca

Dr. DelucaHector F DeLuca, PhD

Emeritus Professor 2011-present
Harry Steenbock Research Professor 1965-2011
Department Chair 1970-1986 and 1991-2005
B.A., University of Colorado
Ph.D., University of Wisconsin-Madison
Hon. D.Sc., University of Colorado
Hon. D.Sc., Medical College of Wisconsin
Hon. Dr. Med., Karolinska Institute

Professor H. F. DeLuca's laboratory has been devoted to the understanding of metabolism and mechanism of action of vitamins A and D. Initially, work in this group centered around describing which forms of vitamin D and vitamin A are active in correcting deficiency disease. In particular, in the 1960's by means of isolation, chemical identification and chemical synthesis, this laboratory demonstrated that vitamin D itself is biologically inactive and must be modified by sequential action by the liver and kidney to prepare the hormone derived from vitamin D, namely 1,25-dihydroxyvitamin D3. Not only the hormonal form but many of its analogs were chemically synthesized in this research group and developed for the treatment of a variety of diseases including osteoporosis, vitamin D dependency rickets, and bone disease of kidney failure. More recently, this laboratory has devoted its efforts to understanding how 1,25-dihydroxyvitamin D3 functions in the target tissues. A receptor which recognizes this hormone has been identified in target tissue nuclei. It has been cloned and its entire amino acid and nucleotide coding sequence has been determined. We have successfully expressed it in large quantities in baculovirus and bacteria and are in the process of crystallizing the protein for three-dimensional structural work. Response elements or specific DNA sequences to which the receptor binds in order to initiate transcription of the genes have also been identified. Other molecular biology techniques are being applied to isolate genes and identify the proteins that are made in response to 1,25-dihydroxyvitamin D3. By locating the receptor in tissues not previously recognized as targets of vitamin D action, new functions for vitamin D have been identified. It is now clear that 1,25-(OH)2D3 serves as a developmental hormone as well as a hormone responsible for regulating calcium and phosphorus. It has also been found to be necessary for reproductive function in females, for the immune system, and for the development of giant osteoclasts responsible for remodeling bone. Our laboratory uses a combination of molecular biology techniques, organic chemical techniques, physiological techniques, and cell biology techniques to learn the molecular mechanism of action of these fat-soluble substances. There is considerable effort dedicated to collaboration with the medical world for the application of the newly synthesized analogs of the vitamin D compounds and of vitamin A compounds for the treatment of disease. The most recent application has been to prevent and arrest such autoimmune diseases as multiple sclerosis and rheumatoid arthritis, and as an anti-transplant rejection drug.