Oxidative stability and polyphenols role in red wine-enriched olive oil emulsions

Vegetable oils are extensively used as food emulsions ingredients for their nutritional and sensory properties. Nevertheless, these matrices are prone to oxidation because they are composed mainly of unsaturated fatty acids. Red wine, due to its rich pool of phenolic compounds, is well recognized as a source of beneficial molecules with antioxidant activity. Wine drinking, however, should be done in moderation or is forbidden for some populations for ethnic or religious reasons. Thus, a suitable way to enjoy the advantages of red wine is to use its phenolic compound-rich extract (RWE). In this study, the antioxidant activity of water-soluble RWE has assessed in water-in-oil (w/o) emulsions based on extra virgin olive oil. After the selection of the right emulsion composition, kinetics of oil oxidation were carried out in oil and emulsions in the presence of an increasing amount of RWE, whose presence was demonstrated to influence the oxidation rate. This behavior was confirmed by monitoring the oxidation process firstly by applying the classical method based on the determination of the peroxide value, then by considering the fluorescence response based on the accelerated test making use of 2,2′-azobis(2,4-dimethylvaleronitrile) (AMVN) and diphenyl1- pyrenylphosphine (DPPP) [1,2]. The comparison between the emulsion aspect confirmed that the extent of the oxidation process was inversely proportional to the RWE concentration. Moreover, by comparing the emulsion structures observed by optical microscopy, no differences in the size of the dispersed aqueous phase were detected with the increase of the RWE, which is an aspect that confirmed that the antioxidant activity was directly proportional to the RWE concentration and thus to the phenolic content present in the system.