SEAFOODplus: New lipid oxidation method

Scientific Alert Note

New, powerful method speeds up analysis of lipid destruction

Understanding lipid oxidation improves the making of healthy seafood. In the project LIPIDTEXT a special, new analytical system has been developed that easily unveils knowledge for the understanding of oxidation. Time to measure oxidation rate has been shortened from days to minutes. The new method has been successfully applied to analyse the impact of temperature on oxidation rates, as well as the pro-oxidative or antioxidative effects of positively and negatively charged ions in the seafood.

Author: Ivar Storrø, SINTEF, Norway

Seafood is our main source of healthy lipids. The most beneficial parts of these lipids are the fatty acids called EPA and DHA. These acids are polyunsaturated and therefore they react very easily with oxygen. The oxidation is a highly unwanted reaction because it leads to several problems. Oxidation is the cause of rancid taste in fish and fish products - and oxidation leads to destruction of the healthy fatty acids such as the EPA and the DHA. In addition, it is assumed that some of the oxidation products might be harmful to humans. Finally, lipid oxidation may also affect texture changes in muscle structures, leading to dry and less juicy products. The process of oxidation thus has to be controlled and minimized. To control this we have to understand the oxidation process.

: The apparatus used for measuring lipid oxidation

Researchers in SEAFOODplus project have developed a special analytical system that easily unveils knowledge for the understanding of oxidation. Time to measure oxidation rate has been shortened from days to minutes. This makes the acquisition of information from these studies very efficient. In addition the method is well suited to measure the effect of antioxidants, which are compounds that reduces the oxidation rates, and prooxidants, which increase the rate of oxidation.

Model results show that lipid oxidation is extremely dependent upon temperature. For each 10 °C increase in temperature the rate of lipid oxidation doubles. A reduction in temperature from 25 to 5 °C reduces the oxidation rate by a factor of four and might increase the shelf life with the same factor. Also a reduction in free iron in processed seafood can reduce the lipid oxidation. The lipid oxidation is proportional to the concentration of iron, and a reduction of 50 % in iron concentration will reduce oxidation by 50 %.

The effect of ions on lipid oxidation shows that cations as sodium, potassium, calcium and magnesium do not influence the rate of lipid oxidation in the test system. Among the anions, neither sulphate nor nitrate influence the rate of oxidation, but chloride and dihydrogenphosphate reduce the rate by 60 and 90 % respectively. The activity of inhibition of the phosphate and the chloride were independent, giving producers of seafood the possibility to reduce the rate of lipid oxidation by more than 90% by the use of the correct ion composition.

: The effect of anions on oxidation

When designing new seafood by mixing different ingredients, these ingredients will contain different levels of prooxidants and antioxidants. Even the same ingredient from two different producers might have different pro- and antioxidant activity. To achieve the maximum lipid stability the level of prooxidants has to be minimized and the level of antioxidants have to be maximized. By the use of the newly developed method, it is possible to measure the pro- and the antioxidant activity in all water soluble ingredients, thus making possible the optimal mixture to ensure the longest possible shelf life. In this way the research in SEAFOODplus ensures better seafood for the consumer.

References

Mozuraityte R., Rustad T., Storrø I.: Prooxidant activity of Fe2+ in oxidation of cod phospholipids in liposomes. Eur. J. Lipid Sci. Technol. 108 (206) 218-226.

Mozuraityte R., Rustad T., Storrø I.: Oxidation of cod phospholipids in liposomes: Effects of salts, pH and zeta potential. Eur. J. Lipid Sci. Technol. 108 (2006) In press.