Properties

Properties of Fish Oil

The properties of fish oil are determined largely by its fatty-acid composition. Because fish oil contains substantial amounts of highly unsaturated fatty acids, particularly EPA and DHA, it behaves differently from many fats that contain larger proportions of saturated or monounsaturated fatty acids.

Fish Oil Remains Liquid at Low Temperatures

Fish living in cold water require flexible cell membranes at low temperatures. Their tissues therefore tend to contain substantial amounts of unsaturated fatty acids, which have lower melting points than many saturated fats.

This is one reason fish oil normally remains liquid at temperatures where more highly saturated animal fats may become firm or solid.

Fish Oil Is Susceptible to Oxidation

The same double bonds that make EPA and DHA highly unsaturated also make them vulnerable to oxidation. Exposure to oxygen, light and heat can gradually produce oxidation products and cause an unpleasant rancid odor or taste.

Manufacturers therefore try to limit exposure to oxygen during processing and packaging. Antioxidants such as tocopherols may also be added to help slow oxidation.

Proper storage after purchase is also important. See How to Store Fish Oil.

Species and Diet Affect the Oil

Fish oil composition varies naturally. Species, diet, water temperature, season and stage of development can all influence the proportions of individual fatty acids.

This means that oil obtained from one fish species is not necessarily chemically identical to oil obtained from another. Commercial products may blend or concentrate oils to achieve a more consistent EPA and DHA profile.

Freshness Matters

The condition of the raw fish and the time between harvesting and processing influence the quality of the resulting oil. Enzymatic activity and microbial degradation can increase free fatty acids and create unwanted odors before refining even begins.

For this reason, careful handling and rapid processing of raw material are important parts of modern fish oil production.

Refining Changes Some Properties

Crude fish oil may contain free fatty acids, pigments, oxidation products, odor compounds and trace contaminants. Refining can reduce many of these unwanted components.

Depending on the intended product, additional processing may also concentrate EPA and DHA or convert the naturally occurring fats into other forms such as ethyl esters and re-esterified triglycerides.

The result is that two products both labeled “fish oil” can differ substantially in fatty-acid concentration, chemical form, flavor, stability and intended use.