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Understanding and inhibition of oxidative deterioration in novel food emulsion systems

Final Activity Report Summary - OXIDEM (Understanding and inhibition of oxidative deterioration in novel food emulsion systems)

The OXIDEM Reintegration Marie-Curie Project is attempting to further elucidate the mechanisms of lipid oxidation in food type oil-in-water emulsions. Its basic target is to propose strategies (such as control of compositional or processing factors, addition of natural antioxidants etc.) in order to minimise the nutritional and organoleptic deterioration of food relevant emulsion products (such as: cream coffee preparations, dairy spread alternatives, fresh cheese types etc.).

During the first year (7 January 2005 - 7 January 2006) research has focused on the following two areas:
(i) investigation on the effect of endogenous parameters against the oxidation of Tween or protein stabilised emulsions;
(ii) determination of the antioxidant potential of various natural antioxidants against the oxidative deterioration of simple model emulsions.

Regarding the effect of compositional factors on lipid oxidation of protein or Tween stabilised emulsions, the followings have been observed:
(i) Both the type of emulsifier and lipid phase exerted an influence on emulsion deterioration. Protein-stabilised emulsions were oxidised significantly slower, than the Tween-based emulsions. Besides, emulsions prepared by sunflower oil (highly rich in polyunsaturated fatty acids) were the most vulnerable to oxidation.
(ii) In any case, a decrease of fat content in the lipid phase of the emulsion led to an increase of oxidative instability. Moreover, as protein concentration increased a higher protection against oxidation was resulted.

Regarding the effect of natural antioxidant on the oxidative deterioration of model food emulsions, it was found that:
(i) Several natural carotenoid extracts inhibited markedly the radical-initiated oxidation of sunflower o/w emulsions, with a dose dependent effect in certain cases. In general, carotenoids, containing polar groups (-OH, C=O, COOH) were more effective than the un-substituted carotenes (e.g carotene or lycopene preparations).
(ii) Combination of carotenoids with other natural antioxidants (tocopherol isomers, ascorbic acid) generally enhanced the antioxidant action.
(iii) The activity of flavonoids against the autoxidation of cottonseed o/w emulsions seems to be dependent on the structure (C-ring) with quercetin exerting a clear antioxidant effect. Mixtures of flavonoids with beta-carotene were not antioxidative.

Regarding the use of various oxidation methods:
(i) Conjugated Dienes-(CD232 nm) Ferric Thiocyante-(515 nm) were the tested spectrophotometric techniques for evaluating the primary oxidation products. Both techniques generally agreed on the final conclusions, with the CD being easier, faster and more reproducible in evaluating the progress of emulsion oxidation.
(ii) The antioxidant hierarchy of carotenoids was similar in terms of both hydroperoxides measurement (CD-232 nm) and the determination of volatile off flavour aldehydes (CG-headspace analysis, SPME extraction).
(iii) The measurement of thiobarbituric acid substances (TBARs-5) has been recently employed as an efficient alternative technique to evaluate secondary oxidation products during the oxidation of the emulsions.