EFFECT OF PHENOLIC ANTIOXIDANT COMPOUNDS ON THE COLLOIDAL PROPERTIES AND ON THE OXIDATIVE STABILITY OF OLIVE OIL O/W EMULSIONS

Oil-in-water (O/W) emulsions are among the main dispersed lipid systems in food. Antioxidants are often used in order to avoid or to reduce the rate of lipid oxidation reactions that, in this case, can be mainly considered as interfacial phenomena. Interaction might take place at this level between the emulsifying agents, antioxidant and the pro-oxidant compounds that affects the colloidal properties of the system and the oxidative stability. 2-Objective i) to study how antioxidant molecules and the interactions between these compounds and emulsifying agents at the interfacial level can modify the colloidal properties of a characterised emulsified system ii) to study the effect of the content and activity of antioxidants on lipid oxidation in emulsified systems over storage time 3- Methods Emulsions were prepared using refined olive oil (20% w/w) and PBS (50mM, pH 7). Gallic acid, catechin and quercetin were chosen as antioxidant compounds while Tween 20 and β-lactoglobulin were used as surface active agents. Surface tension measurements, ξ-sizing and ξ-potential were carried out on model solutions containing the phenolic compounds both alone and in combination with the emulsifying agents. Particle size distribution, bulk rheology, lipid hydroperoxide content, TBAR’s and tryptophan fluorescence determinations were carried out on the emulsified systems over storage time (33 days at 40°C). 4-Results All the antioxidants proved to be slightly surface active with catechin being the most efficient among them. In emulsions, quercetin and catechin concentrations were negatively correlated against droplet size. The antioxidant concentration used to test the emulsions' oxidative stability was set to10-4 M according to colloidal and rheological measurements in order to have the maximum amount of antioxidant solubilised in the system without altering their overall colloidal properties. Gallic acid, despite its partitioning in the water phase, due to its polarity proved to delay both the primary and secondary oxidations and to retard the formation of oxidation products. 5- Significance of the research to the food engineering field This research could find obvious practical application in the development of innovative formulated multi-phased food and beverages as well as nutraceuticals.