Fish products and Byproducts Technology

Unit 9 - Fish meal and fish oil

9.8.1.c. Processing of fish oil
In general terms, all crude oils and fats contain minor amounts of non triglyceride substances. While some of these are considered beneficial to the stability of the oil, such as tocopherols and astaxanthin (in salmon and krill oils) which protect the oil from oxidation, other impurities are objectionable because they render the oil dark colored, cause it to foam or smoke or are precipitated when the oil is heated in subsequent processing operations. Other impurities reduce acceptability because of the flavors and odors they produce in the fat or because they reduce stability and shelf life of the foods to which the fats are added.
Some impurities are common to all fats regardless of the source or end use:

• Suspended matter (insoluble impurities).
• Naturally occurring color bodies.
• Free fatty acids.
• Volatile, malodorous compounds dissolved in the fat or oil.

These non-triglyceride substances have also been classified according to their effect:

• Hydrolytic - moisture, insoluble impurities, free fatty acids, mono and diglycerides, enzymes, and soap.
• Oxidative - trace metals, oxidation products, pigments, tocopherols, and phospholipids.
• Catalyst poisons - substances which inhibit the hydrogenation reaction e.g. phosphatides, oxidation products, and compounds containing nitrogen, sulfur, and halogens.
• Miscellaneous - hydrocarbons, terpenes, resins, sterols, waxes, trace metals and sugars whose effect is less well known but can be classified as contaminants and also may have an effect on the final flavor of the oil

Processing steps and the compounds removed by them in purification of fish oil
Carbon Treatment
Removal of dioxins, furans, and polyaromatic hydrocarbons (PAH). This can be performed on the starting crude oil if the oil is to be sold into the non-industrial market.
Oil Storage
Insoluble impurities, trace moisture and some phospholipids will precipitate out in the tanks. The combination is known as "foots".
Degumming
Phospholipids, sugars, resins, proteinaceous compounds, trace metals and other materials.
Alkali Refining
Free fatty acids, pigments, phospholipids, oil insoluble material, water soluble material, trace metals
Water Washing / Silica Treatment: Soaps, oxidation products and trace metals
Drying: Moisture
Adsorptive Bleaching& Carbon Treatment
Pigments, oxidation products, trace metals, sulfur compounds, dioxins, furans, PAH and possibly some PCB's
Winterization
Higher melting triglycerides, waxes. Used to enhance the unsaturated triglycerides
Deodorization
Free fatty acids, mono-diglycerides, aldehydes, ketones, chlorinated hydrocarbons and pigment decomposition products. This is usually the finishing step and results in a bland tasting oil.
Vacuum Stripping or Thin Film, Molecular or Short Path Distillation
Removal of chlorinated hydrocarbons, fatty acids, oxidation products, PCB and free cholesterol. Sometimes this step is used as a replacement for the deodorization step