CDR FoodLab – Efficient Analysis of Fish Oil

Testing and analyzing is one of the fundamental aspects of any industry involving food resources or beverages. The analyses can be performed at different stages and work for the best as possible yield and quality of the final product. Sometimes it is the final product that needs to be analyzed and checked.

Fish Oil
Fish oil has been produced since the 19th century for leather tanning, for the production of soap, glycerol and other non-food products, and lately for the production of fish oil supplements. Other uses are in food such as in margarine and shortenings or for medical and industrial purposes. Fish oil is rich in healthy free fatty acids and new findings have led to an increased usage of fish oil as a food supplement.
The fish oil and fish meal industry uses the so-called industrial fish as raw materials. These are fish that are not used for the fresh fish market because they cannot be used for direct human consumption. They are too small or break down or turn rancid too quickly for economic storage and subsequent heading, gutting, cleaning and processing. This kind of fish, small and oily, are the main part of the catch.

Some examples of industrial fish:

  • Gadoids (cod-like fish)
  • Clupeids (herrings)
  • Scombroids (mackerel)
  • Elasmobranchs (sharks and rays)
  • Salmonoids (salmon and other related fish)
  • Crustaceans (small crustaceans, carapaces and shells)

A wide variety of fish species is used for the production of fish oil and meal in different countries. Fish meal is a product used for animal feed.

The Production of Fish Oil and Meal
The same production flow produces both fish oil and fish meal. The two products are different but closely connected. To understand this, it is necessary to consider that the components of the industrial fish are: a solid part (fat-free dry matter), oil and water. The table below shows the composition of the material at each stage of its flow through the process and is based on the assumption that the raw fish contain 70 % water, 18 % solids and 12 % fat.

The composition of the intermediate products in this example is as follows:

FoodLab Fish Oil Table

Fish oil and fish meal processing is focused on separating these three components from each other. Reducing fish to oil and meal can be done in a number of ways, but some processing steps are common to all methods. You cannot prescind from:

  • Heating which coagulates the protein, ruptures fat deposits and liberates oil and physic-chemically bound water
  • Pressing or Centrifuging which removes a large fraction of the liquids from the mass
  • Separation of the liquid into oil and water (stickwater)
  • Evaporation of the water into a concentrate (fish solubles)
  • Drying of the solid material and added solubles to remove sufficient water from the wet material to form a stable meal
  • Grinding the dried material to the desired particle size

Fish Oil Production
Here we underline some important aspects in reducing fish to oil.

High Temperature
This is an important prerequisite for efficient separation of the three components. The best performance of the production plant will be obtained at the highest possible temperature which, at atmospheric pressure, would be l00 °C. Some experiments, however, have shown that the walls of the fat cells are broken down before the temperature reaches 50 °C. The oil is then free, and theoretically it should be possible to separate it from the solid material.

Separation of the Fat Component
The press and the pre-strainer transform the fish in a liquor consisting of water and varying amounts of oil and dry matter. The oil content is related to the proportion of oil in the fish. The separation of the three components of the press liquor, sludge, oil and water, is based on their different specific gravities. If press liquor is left for some time in a tank, it will settle out into three layers: sludge at the bottom, water in between and oil at the top. Production plants use centrifuging for this operation that can be efficiently accomplished in seconds.
Oil Polishing – Once the oil is extracted it needs a final refining that is performed in special separators. This step is completed at the factory before the oil is pumped into storage. Polishing is facilitated by using hot water, which extracts impurities from the oil and thus ensures stability during storage.

Fish oil needs to be stored before being sold and some precautions are taken regarding residual water, temperature, contamination by sludge and water.
This is a crucial stage for analysis, the mainstay for the quality control and shelf life of the oil. The varieties of fish from which the oil is extracted influence the times and temperatures of preservation. Chemical analysis can help to identify the acceptable tolerance for storage of the fish oil and to determine which temperature assures the best and longer preservation. For example Shad oils have a high oxidative deterioration while Garfish oil shows a greater stability against oxidation. These differences can be checked using a quick and reliable analytical system.

Fish Oil Parameters and Methods
From the start of the fish oil production process the oxidation parameter must be kept under control. Systematic sampling and analysis are used to provide important information to make the best choices during the whole process.

The analysis that can help the fish oil industry to manage a high performance quality checks are:

  • Peroxide Value – To establish primary oxidation product levels. These compounds, with others resulting from further decomposition, are responsible for the rancid flavours that develop
  • p-Anisidine Value – To establish secondary oxidation product levels, for the same reasons of PV. Nevertheless the AV is more indicative of quality state
  • Free Fatty Acids – Is still the most reliable parameter for oil quality and yield assessment

A number of chemical, physical and sensory methods have been developed for the assessment of quality. The analytical work is made difficult by some aspects:

  • The nature of the unsaturated fatty acids
  • The need to store at low temperatures in an inert atmosphere the oil before analysis
  • The tendency of saturated oil fractions to precipitate during cold season in large storage vessels, then the need to mix the oil before sampling

Moreover the test methods employed by the user of fish oil for hardening purposes are often divided into two groups, the first being applied on receipt of a consignment to check the fundamental parameters and the second, more detailed examination, as soon as possible thereafter, but in any case before the oil is used in the refinery. The purpose of this second examination is to determine refining procedures.
The fish oil industry cannot prescind from the information a good and rapid analysis can provide. It ensures production to a high quality standard and product optimization. Performing these analysis in the production plant using the reference methods can be very problematic since they need a fully equipped chemical laboratory, skilled staff and a long and delicate procedure.

Fish Oil Analysis with the FoodLab
The CDR FoodLab system can test fish oil in a rapid, simple and reliable way without involving a chemical laboratory, inside or outside the production facility. It can analyze Peroxide Value, p-Anisidine Value, Free Fatty Acids and Soaps in fish oil. Thanks to the optimized methods and the colorimetric technology the analysis can be performed in few minutes and the results are immediately available, facilitating correct conservation of the oil and assisting decision making about the different batches.


  • Analyses are very quick and use an analysis method that is compliant with the reference method
  • Analysis can be performed at any time in the production plant, in great quantities
  • Time saving and drastic reduction of analysis costs
  • A simple and rapid analysis method that anyone can perform
  • Prefilled cuvettes and reagents that do not require a laboratory or complicated chemical disposal procedures

Dr Simone Pucci
Head of CDR Research and Development Chemical Laboratory

FAO, Fishery Industry Division, “The production of fish meal and oil” FAO Fish. Tech. Pap. (142) Rev. 1: 63p