The effect of storage temperature, pH, and homogenization pressure on the oxidative deterioration of Tween 20 and sodium caseinate sunflower oil-in-water emulsions was studied by monitoring conjugated dienes (CD), lipid hydroperoxides (LH), and thiobarbituric acid reactive substances (TBARs). CD increased linearly with storage time, and the rate constant was temperature dependent according to the Arrhenius equation with an activation energy equal to 37.5 kJ mol −1 . The increase in LH and TBARs with temperature (5-60°C) was in good agreement with CD variation. Tween-stabilized emulsions oxidized faster as pH increased from 3 to 7, whereas a different behavior was observed in emulsions stabilized with sodium caseinate or a mixture of both emulsifiers. A change of homogenization pressure (30-900 bars), reflecting variation of emulsion average droplet size, had no effect on the oxidative stability of the emulsions.

This work attempts to determine any relationship between certain endogenous parameters and the oxidative deterioration of protein-stabilized oil-in-water emulsions. The contribution of compositional factors (e.g., type and amount of emulsifier, fat phase, etc.) is further elucidated. Among 10% cottonseed o/w emulsions prepared by 1% emulsifier (Tween, sodium caseinate, or whey protein), lipid autoxidation (at 40°C) was much faster in the Tween emulsion than in the protein ones, with whey protein presenting a clear antioxidant effect. Increase in protein concentration (0.5-2% w/w) led to a decrease in droplet size but an increase in oxidative stability, in terms of conjugated diene hydroperoxides formation at 232 nm. The type of lipid phase significantly affected the rate of thermal oxidation at 60°C. In the most oxidatively vulnerable sunflower-oil-based emulsions, an increase in fat content (10-40%) resulted in a reduction of oxidative deterioration. By selecting a more concentrated emulsion (20% o/w, 2% emulsifier), in order to structurally approach real novel food products, any influence of the composition of the emulsifier (combination of Tween and sodium caseinate preparation) was subsequently tested. An increase in protein proportion in the emulsifier was found to inhibit proportionally the oxidative instability of the emulsions, as evaluated by the determination of both primary (conjugated diene and lipid hydroperoxides) and secondary [thiobarbituric acid-reactive substances (TBARS)] oxidation products.

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