Last Updated July 23, 2019

A Scientist Explains Fermented Cod Liver Oil Oxidation Results

Dr. Subramaniam Sathivel has been kind enough to analyze oxidation test results of our Fermented Cod Liver Oil.  What did he have to say?

  • Our Fermented Cod Liver Oil is a good quality oil
  • It is a good source of Omega-3 Fatty Acids
  • Free fatty acids are produced in the extraction process, not from lipid oxidation
  • Our Fermented Cod Liver Oil is well protected by natural antioxidants
Below is his full interpretation and explanation of the results to us:


Dear Dave,

I reviewed the reports from Mid West Laboratories, Inc. and Eurofins Laboratories for your Fermented Cod Liver Oil.

Midwest Laboratories, Inc. Report of Analysis FCLO 20946ABS September 23, 2015
Midwest Laboratories, Inc. Report of Analysis FCLO 07252ABS September 23, 2015
Midwest Laboratories, Inc. Report of Analysis FCLO 05751ABS September 23, 2015
Midwest Laboratories, Inc. Report of Analysis FCLO 31641ABS September 23, 2015
Midwest Laboratories, Inc. Report 15-265-4118 FCLO September 22, 2015

Eurofins Nutritional Analysis Center Certificate of Analysis AR-15-QD-115048-02
September 23, 2015

The independent analytical labs analyzed a total of seven Fermented Cod liver Oil samples and provided data for fatty acids profiles and thiobarbituric acid (TBA) values. The secondary lipid oxidation products (aldehydes) are evaluated by the measurement of malondialdehyde (MDA) reacting with thiobarbituric acid (TBA). The TBA value of your fish oils was an average of 0.32 mg MDA /kg oil, which is well below the acceptable level. Consumers may accept edible oil with TBA as high as 7-8 mg MDA/kg oil (Huss 2011).

Please note that lipid oxidation is a chain reaction and, in general, oxidized oil will have high amount of aldehydes. Dr. Martin Grootveld, Leicester School of Pharmacy, De Montfort University, Leicester, United Kingdom, analyzed your oil for lipid oxidation products (aldehydes and/or their conjugated hydroperoxydiene precursors) using one- and two-dimensional multicomponent H NMR technique. According to Dr. Martin Grootveld’s report they did not find aldehydes and/or their conjugated hydroperoxydiene precursors in your oil sample. Dr. Grootveld’s findings are in accordance with TBA values of your oil that were analyzed by the above-mentioned laboratory. This indicated that your oil had no or undetectable levels of secondary oxidized products including aldehydes.

The above-mentioned commercial analytical labs report showed an average of 1.19% trans fatty acids in your oil. It is normal to have very low level of trans fatty acids. Some labs may not report trans fatty acids in fish oil because they are, if present, present only at undetectable level or at levels less than 1%. What is free fatty acid? Oil molecules are known as triglycerides, which means three free fatty acids are attached to a glycerol as shown in Figure 1. Three fatty acids could be saturated or unsaturated or two unsaturated and one saturated or one unsaturated and two saturated fatty acids. Therefore, we can find many different triglycerides in oil. Our body absorbs only free fatty acids, monoglycerides (one fatty acid bonded with a glycerol) and some diglycerides (two fatty acids bonded with a glycerol), which means body cannot absorb oil with the triglyceride form. Pancreatic lipase enzyme in our intestine breaks down triglycerides into free fatty acids and monoglycerides or diglycerides and then our body absorbs them. 

Triglycerides can also breakdowns break down into free fatty acids during extraction and processing of fish oil. Either water or lipases (both are present in animal tissue) hydrolyzes triglycerides and produces free fatty acids. Please note that free fatty acids in oil are not a compound resulting from a lipid oxidation reaction. I think there may be free fatty acids forms of DHA and EPA available in the nutraceutical market. There is limited research that shows that the free acid form of omega -3 provides more health benefits than triglyceride forms. In edible oil refining, we estimate refining loss based on the amount of free fatty acids in the oil. Your oil sample had an average of 17.3% free fatty acids, which is relatively high. Please note that your production technique of cod liver oil is very different than the traditional methods. In general, unrefined fish oil or unrefined edible oil has a high amount of free fatty acids. Sodium hydroxide is a base used to neutralize free fatty acids in edible oil. There are other techniques such as adsorption and distillation that can be used to remove free fatty acids. As I mentioned in another paper, free fatty acids have a tendency to oxidize; however, your oil has a very low level of TBA. It may be due to the presence of antioxidants in the oil. Your vitamin analysis showed that the fermented cod oil had a significant amount of vitamin A, which is known as an excellent antioxidant. It absorbs free radicals that result from lipid oxidation. Lipid oxidation is a chain reaction and we can delay or minimize lipid oxidation by removing free radicals. Your company uses amber bottles, which prevents or minimize light penetration into the bottle. UV light is one of the factors that promote lipid oxidation. In general, all oil has a tendency to oxidize regardless of free fatty acid content when they are exposed to light a long period of time or subjected to heat.

In conclusion, the data shows that your cod liver oil is a good quality oil and a good source of omega-3.

Again, free fatty acids in the oil are not compounds resulting from lipid oxidation reactions. In other words, they are not aldehydes.

If you have any questions, please let me know.

Subramaniam Sathivel, Ph.D. Professor of Food Processing Engineering

About Dr. Sathivel

Dr. Sathivel 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.


Huss, H. H. (1988). Fresh fish--quality and quality changes: a training manual prepared for the FAO/DANIDA Training Programme on Fish Technology and Quality Control (No. 29). Food & Agriculture Org..

Schnepf, M., Spencer, G., & Carlort, J. (1991). Chemical and sensory characteristics of stored menhaden oil/soybean oil blends. Journal of the American Oil Chemists Society, 68(5), 281-284.