A high-quality fish oil has little taste and it is difficult to tell the difference from a normal cooking oil.
Fish oil is particularly rich in healthy polyunsaturated omega-3 fatty acids, which makes it particularly susceptible to rancidity. Upon oxidation of polyunsaturated fatty acids, a complex mixture of small molecules is formed, providing odour and taste.
Need for better analysis
"Current approved standard analytical methods for harsking, such as peroxide and anisidine value, are not good enough to ensure high-quality fish oils. A range of analytical methods must be used to achieve the most accurate picture of oil quality," said researcher Stine Grimmer.
A strategic research across Nofima's divisions has developed alternative quality of fish oil - an analysis that measures levels of specific oxidation products in oils. Methods have been tested on a number of different types of fish oils with different degrees of rancidity, and have been compared to the standard analysis methods. The new quality analysis is increasingly able to document the degree of rancidity compared to the original analysis methods.
Why is it so important to know about the degree of rancidity of fish oil?
A rancid fish oil with unwanted tastes and odours can cause repulsion. After dissolving in the stomach, a capsule of poor quality oil can cause the regurgitation of rancid flavour. Reduced quality fish oils can also cause detainment of positive health effects of omega-3 fatty acids.
"There are indications that rancid oil inhibits the cell's own antioxidant system and reduces the inflammatory effects of omega-3 in cell models," said Dr Grimmer.
The research is financed by the Fishery and Aquaculture Industry Research Fund (FHF) and the Norwegian Research Council.