Exploring the Use of Hydroxytyrosol and Some of Its Esters in Food-Grade Nanoemulsions: Establishing Connection between Structure and Efficiency.

The efficiency of HT and that of some of its hydrophobic derivatives and their distribution and effective concentrations were investigated in fish oil-in-water nanoemulsions. For this purpose, we carried out two sets of independent, but complementary, kinetic experiments in the same intact fish nanoemulsions. In one of them, we monitored the progress of lipid oxidation in intact nanoemulsions by monitoring the formation of conjugated dienes with time.

Interfacial kinetics in olive oil-in-water nanoemulsions: Relationships between rates of initiation of lipid peroxidation, induction times and effective interfacial antioxidant concentrations.

Hypothesis: A detailed quantitative description of the effects of antioxidants in inhibiting lipid peroxidation in oil-in-water emulsions can be achieved by determining the relationships between the rates of initiation of the lipid peroxidation reaction, the length of the induction period preceding the propagation step of the radical oxidation process and the effective antioxidant interfacial concentrations.

Experiments: We successfully prepared and characterized a series of olive oil-in-water nanoemulsions and allowed them to spontaneously oxidize. Their oxidative stability was evaluated by carrying out in the presence, and absence, of antioxidants derived from gallic acid, by monitoring the formation of primary oxidation products with time, by determining the corresponding induction periods, and by determining the effective interfacial concentrations of the antioxidants in the intact emulsions.

Effects of droplet size on the interfacial concentrations of antioxidants in fish and olive oil-in-water emulsions and nanoemulsions and on their oxidative stability.

Hypothesis: One fundamental and unsolved question in colloid chemistry, and also in the food industry, is whether molecular distributions, specifically the interfacial concentrations of antioxidants (AO), are independent of the droplet sizes. Pseudophase kinetic models, widely employed to interpret chemical reactivity in colloidal systems and to determine antioxidant distributions, assume that they are independent.

Experiments: To prove, or discard, the above hypothesis, we prepared and characterized a series of olive and fish oil-in-water nanoemulsions with different droplet sizes, carried out a kinetic study to evaluate their oxidative stability, both in the presence and absence of gallic acid (GA), and determined its interfacial concentrations.