Collaboration between the partners in the LIPIDTEXT project is still progressing very well. The joint work between IIM, Unilever, CTH and DIFRES on evaluation of the same antioxidants in different systems has now been expanded also to include NTNU/SINTEF. Thus, the ability of caffeic acid to reduce lipid oxidation has now been evaluated in emulsions, liposomes, washed cod muscle, fish mince from salmon and horse mackerel and will in the near future also be evaluated in a more complex system, namely fish paté enriched with fish oil. The results in liposomes obtained this year showed the same prooxidative effect of caffeic acid as was observed in the previous period in emulsions. In contrast, the results obtained in 2007 in the washed cod model showed the same strong antioxidative effect as observed previously in fish mince. Moreover, the results have also indicated that caffeic acid is able to reduce protein oxidation in the ice stored cod muscle model. These data are unique and will form the basis for a joint review paper on the effect of caffeic acid in different fish based food models. The data showing that caffeic acid has a strong antioxidative effect in fish mince has also formed the basis for a demonstration project that will be initiated very soon.
The pioneering work performed with the liposomes assay has resulted in a new theory for the oxidation mechanisms for iron catalysed lipid oxidation that is different from the generally accepted theory. According to the new theory oxidation should not be regarded as a 3 stage process (initiation, propagation and termination), but rather as an equilibrium process where the recycling of iron generates radicals and the radical concentration is kept constant due to a termination reaction that balances the production rates of radicals. The liposome assay work has also resulted in the determination of important kinetic rate constants for iron and haemoglobin catalysed oxidation. On the basis of the oxidation rate data obtained, it has also been possible to make a mathematical model that can predict the oxidation rate in liposomes in dependence of a number of factors such as temperature, iron concentration and oxygen concentration. The model has been applied on emulsions and promising results have been obtained, but further refining of the model is still necessary. Taken together, these results indicate that it is possible to obtain very valuable information about oxidation mechanisms and kinetics in a relatively simple system like liposomes and that it is possible to make mathematical models that can predict oxidation in these systems. The principles should be tested in more complex food models in the future. The results have also demonstrated that the assay has a potential for being used to evaluate the efficacy of antioxidants and for developing predictive models for antioxidant efficacy in both liposomes and emulsions.
One of the important aims of LIPIDTEXT is to improve our understanding of the link between protein and lipid oxidation. During 2007 data on protein oxidation have been obtained in washed cod muscle, fish paté and in the Marie Curie project CONTROXFISH, which has been associated to LIPIDTEXT. The results have shown that lipid and protein oxidation seem to occur simultaneously and that both processes seem to be influenced by the same factors (e.g. presence of haemoglobin, temperature). However, it has not been possible to deduce to which extent the two processes influence each other. It is expected that the planned experiment on the effect of oxidised proteins on fresh lipids and vice versa will help elucidate this question. Moreover, the results have indicated that the more complex the matrix is the more difficult it will be to obtain reliable, reproducible results. Therefore, new more specific and sensitive methods for detecting protein oxidation are required.
Important data about the effect of caffeic acid on the level of endogenous antioxidants have been obtained and from this it can be concluded that an important antioxidant mechanism for caffeic acid is its ability to regenerate tocopherol radicals.
The work on protein markers for texture in rainbow trout has made significant progress in 2007. Hence, seven proteins that may be potential markers for texture have been identified, but further work is still necessary to confirm the results.
Another central aim of LIPIDTEXT is to investigate whether there is a link between protease activity, texture changes and lipid oxidation. Investigations on this issue were intensified in 2007 using stressed and unstressed cod from the ETHICOD project and stressed and unstressed rainbow trout from Denmark. So far, no clear relationship has been found, but work will be continued to further investigate this matter.
The collaboration with other projects in pillar 4 (4.1 and 4.4) has been continued. Thus, planning of experiments to reduce oxidation during protein hydrolysis of fish is in progress in collaboration with the PROPEPHEALTH project. The planning of the experiment on the combined antioxidant effect of commercial fibres and antioxidants in fish mince is also progressing in collaboration with CONSUMERPRODUCTS.