Rosita Handcrafted Ratfish Liver Oil™

One of Nature's Rare Wonders

Monitoring the quality of Rosita Ratfish Liver Oil™

Oxidative rancidity

As soon as oil is extracted, it begins to undergo a number of chemical changes, including the oxidation of lipids (fats), which may impact flavour, aroma, and nutritional quality. Vitamins and other nutrients present in the oil may be partially destroyed by free radicals produced during the lipid oxidation process.

Oxidized lipids are nutritionally useless, damage cells, and generate free radicals. Free radicals are unstable molecules that come in many shapes, sizes, and chemical configurations, and are capable of damaging cells and tissues throughout the body. Free radicals are implicated in aging, cataracts, cancer, heart disease, and many other conditions.

Oxidation of lipids results in what is known as ‘oxidative rancidity,’ and occurs in three phases. During the initial phase of lipid oxidation, oxygen combines with unsaturated fatty acids to produce lipid hydroperoxides and free radicals. This phase occurs in the presence of chemical oxidisers, metals, or enzymes. Heat and light also increase the rate of this and other phases of lipid oxidation.

During the next phase, the lipid oxidation products formed during the initiation phase react with additional lipid molecules present in the oil, to form further oxidation products, in a process termed auto-oxidation. Auto-oxidation is a major deterioration reaction that affects fats and oils.

In the final, termination phase, relatively unreactive substances are formed including hydrocarbons, aldehydes and ketones.

Tests to measure oxidative rancidity

Peroxide value

The primary products of lipid oxidation are hydroperoxides which generally are referred to as peroxides. These are measured using the Peroxide Value test (PV). This is an indication of the initial stages of oxidation, and is a measure of hydroperoxide concentration. It is actually defined as the milliequivalents of peroxide per kg of oil.

Rosita Ratfish Liver Oil™ has a low peroxide value of 4.15 Meq/Kg. (Determination of Peroxide value by IUPAC standard method 2.501).

(Stringent European Pharmacopoeia Commision max: 5 Meq/Kg).

The concentration of peroxides is not a definitive measure of the extent of oxidation. This is because of the transitory nature of the peroxides i.e. their fast decomposition, resulting in a decrease in the peroxide value as secondary oxidation products appear. This is why we measure the anisidine value to get a better picture of the extent of oxidation.

Anisidine value

Lipid hydroperoxides gradually breakdown, forming volatile aldehydes, responsible for the rancid odour and flavour, and leaving behind non-volatile reaction products which are normally measured using the p-Anisidine test.

High anisidine values are generally an indication that an oil has been oxidised.

Rosita Ratfish Liver Oil™ has an extremely low anisidine value of 0.66 (expressed as anisidine value units). (Determination of Anisidine value by IUPAC standard method 2.504).

(Stringent European Pharmacopoeia Commision max: 10).

The total oxidation (TOTOX) of the oil can now be evaluated using both the peroxide and p-anisidine values.


The peroxide and anisidine values can be combined into the TOTOX value.

TOTOX value for an oil is calculated as the anisidine level plus two times the peroxide level, or: Totox = AV + (2 x PV)

Rosita Ratfish Liver Oil™ has a very low TOTOX value of 8.96 Meq/Kg.(Stringent European Pharmacopoeia Commision max: 20 Meq/Kg).

Such a low TOTOX value for Rosita Ratfish Liver Oil™ suggests that it is exceptionally fresh, and has not been abused by heat or light contact. Antioxidants present in the oil may also play an important role in helping to maintain exceptional freshness.

Acidity of oil

The acidity of oil is dependent on the amount of free fatty acids present, and may be measured as either the acid value or as the free fatty acids (FFA).

The acidity level is also a good indicator of the care and attention to detail of the harvesting and extraction process. Acidity in the liver may start to increase as soon as the fish are harvested. This explains why the fish must not be allowed to sit, but brought to shore without delay, at the correct temperatures. Low acidity extends the shelf life, and maintains a higher level of quality.

Acid value

Rosita Ratfish Liver Oil™ has a very low acid value of 0.40 mg KOH/g.

Free fatty acids

Free fatty acids in a fat are expressed as % of a fatty acid common to the product being tested. Frequently, values are expressed as % oleic acid for olive oil, and this is the case for our ratfish liver oil.

Free fatty acids is an indication of another type of rancidity, termed hydrolytic rancidity, but other lipid oxidation products can also produce acids.

Rosita Ratfish Liver Oil™ is a superior category of fish liver oil extracted from ratfish liver solely by the ancient principles pointed out by nature herself. The acceptable levels of acidity (free oleic acid level) for an oil to be classified as "Extra-Virgin" is under 0.8%. Premium Extra-Virgin designates oil that has an acidity level under 0.5%.

Rosita Ratfish Liver Oil™ was tested at the Institute of Aquaculture and shown to have only 0.2% acidity, making it one of the best oils around in terms of acidity, with values lower than many of the best extra-virgin olive oils.

Our Oil is retested periodically to ensure that premium standards are maintained.


From our beautiful nature - island of Doenna, Helgeland - Norway

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