Propolis is known to possess antioxidant activity. However, there is no information on this activity in emulsions O/W. The protective effect of propolis on the oxidation and rheological properties of emulsions O/W containing wheat germ and almond oils was evaluated. Emulsions O/W were prepared with different concentration of propolis extract, almond oil and wheat germ oil. All emulsions physically stable without phase separation were stored at 37 °C for 9 weeks. Chemical composition of propolis was established by Gas chromatography coupled to mass spectrometry. Rheological characterization of different emulsions was performed evaluating consistency index and flow behavior index. The oxidation was monitored by measuring the lipid hydroperoxides and thiobarbituric acid-reactive substances (TBARS) methods. Flavonoids, phenolic acid esters, and aromatic acids were the main groups of compounds found in propolis. The results showed that popolis was good antioxidant in the concentration of 0.02 and 0.04% when lipid phase was constituted by almond oil. The rheological behavior is typical of a non-Newtonian fluid, being almond oil more adequate for having a higher stable O/W emulsion.

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Thymus vulgaris (thyme) is an aromatic plant and its essential oil has been applied as antimicrobial and antioxidant due to the presence of phenolic compounds. However, after steam distillation, the deodorized plant material is rejected, despite the possible presence of bioactive compounds. Ethanolic thyme waste extract revealed the presence of benzoic acid, 4-hydroxybenzoic acid, ferulic acid, caffeic acid, and sinapic acid. This waste thyme extract had the capacity for preventing the formation of primary and secondary lipid oxidation products in emulsions O/W (oil in water), constituted by diverse proportions of wheat and almond oils, without interfering with the viscosity parameters, for 10 weeks, at 37 °C. The increasing proportion of almond oil (≥50%) in the emulsion increases its resistance to oxidation, which is improved with the presence of an optimal concentration of tested thyme waste extract (0.02% and 0.04%). The waste thyme extract can, therefore, be used as an antioxidant either in food or pharmaceutical emulsions O/W, replacing the synthetic antioxidants.

This study compared the capacity of propolis extract (PE) and thyme waste extract (TWE) to prevent the oxidation of oil in water (O/W) emulsion, as well as their impact on emulsion apparent viscosity (AV) in the presence of wheat germ and almond oils as lipid phase. For this, central composite design (CCD) and principal component analysis (PCA) were performed. Oxidation process was monitored by evaluating the formation of primary and secondary lipid oxidation products, at the same time the AV behavior was determined evaluating consistency index and flow behavior index. The results revealed that the increase of PE% and TWE% decreases TBARS (Thiobarbituric Acid Reactive Substances) and hydroperoxides formation. Viscosity increases with the rise of TWE% over (0.04%), whereas lower concentrations of PE% decreases it. Those results have been confirmed in the PCA analysis. TWE showed higher resistance to oxidation, although PE was more effective as antioxidant than TWE.