Salmon oil & oxidation

What is oxidation?

Oxidation is a chemical reaction, also referred to as a redox reaction, which involves the transfer of electrons from a reducing agent to another substance, the oxidising agent. Iron rusting is a familiar example of oxidation (Fe²⁺ —> Fe³⁺+ e^–). In this process, iron releases an electron and oxidation/rust is formed. Fats, such as salmon oil, can also oxidise. This chemical process can cause (salmon) oil to become rancid. If salmon oil is excessively oxidised, it is no longer suitable for use in feed. Antioxidants delay this process and effectively extend the shelf life of a product.

Oxidation

Oxygen hydrolyses the fatty acids, causing them to detach from glycerol. These detached fatty acids can continue to oxidise, as the following process describes. Oxygen oxidises the free fatty acids into peroxides. These peroxides are then degraded further into substances including radicals. Radicals (e.g. free oxygen) are molecules or atoms that are deficient in an electron and to achieve stability they ‘steal’ it from other molecules. These radicals in turn react with other free fatty acids causing the process to repeat itself triggering a chain reaction. This repetitive reaction leads to a fat/oil becoming rancid thus making it unsuitable for use. The chain reaction can be accelerated by factors including heating, exposure to UV light and exposure to air. Oxidised fat has a characteristic sharp, rancid odour. An antioxidant can be added to fat to prevent oxidisation. Antioxidants are able to neutralise free radicals, preventing oxidation and the subsequent chain reaction.

Salmon oil

Salmon oils from E.F.S are very rich in high-quality unsaturated fatty acids. Unsaturated fatty acids are more susceptible to hydrolysis and therefore to oxidation. To prevent oxidation, salmon oils from E.F.S. are protected with an antioxidant.

In addition to added antioxidants, salmon oil also contains a naturally occurring antioxidant: astaxanthin. This natural antioxidant already offers good protection during the production of salmon oil. Astaxanthin also gives salmon oil its typical colour (reddish-brown). Extra antioxidants are added during the production process to provide long-term protection for salmon oil.

Various products can be used as antioxidants.

Tocopherols (vitamin E) Ascorbic acid (vitamin C) BHA (Butylated hydroxyanisole) BHT (Butylated hydroxytoluene) Citric acid Rosemary extract Alpha-lipoic acid Gallic acid

Selenium Carotene (Beta-carotene) Tannins Natural essential oils (such as rosemary, cloves and thyme) Tocopherol acetate Calcium propionate Cinnamaldehyde

BHA, BHT and tocopherols are most commonly used in salmon/fish oil.

Measuring oxidation

Fresh salmon oil has the scent of fresh fish. Oil that smells rancid indicates that oxidation has already occurred. So the sense of smell is an important parameter for oxidisation, but is not, however, an entirely objective assessment.

Various methods are used to indicate and measure the oxidation process of salmon oil.

One commonly used method is the peroxide value, which is a measure of the concentration of peroxides. This widely used method indicates the degree of oxidation in fresh oil. The target value is <10 mEq/kg. Values above 30 mEq/kg should be avoided. The peroxide value is especially important in the initial stages of lipid degradation. With a high degree of oxidation and therefore a high breakdown of peroxide, the peroxide value can be low even though the oil is still oxidized.

FFA value
The FFA (Free Fatty Acids) value provides a certain degree of insight into the extent of oxidation. An FFA value <10 g/kg is sufficient and <5 g/kg is low.

Another oxidation determination method is the anisidine value. Aldehydes (the degradation products of the peroxides) are measured. These aldehydes cause the characteristic rancid smell of oxidised oils/fats. The target value is <30 mEq/kg.

The TOTOX value is calculated by multiplying the peroxide value x 2 and adding the anisidine value (totox = AV + 2*PV). The TOTOX value provides a complete picture of the degree of oxidation in a fat.

The iodine value is sometimes also stated to indicate the degree of oxidation. However, this value only indicates the number of double bonds, which shows the degree of susceptibility to oxidation of a fat.

Storing & processing

Storing and processing the salmon oil correctly is vital to optimally protect the oil. Salmon oil must be protected from external influences (direct sunlight, high temperatures and oxygen) and any contamination in the storage tank or IBC must be avoided. E.F.S. recommends keeping the salmon oil packaging closed as much as possible. ICBs should be emptied from below and agitators should not be used in the tank to prevent introducing air. Exposure to air will greatly accelerate the oxidation process.

Salmon oil does not need to be heated as it remains liquid down to -10° Celsius.

If you have any further questions, please contact E.F.S.