Comparative study of the phenolic profile and antioxidant activities of Moringa (Moringa oleifera Lam.) and Jujube (Ziziphus Lotus Linn.) leaf extracts and their protective effects in frying stability of corn oil

Numerous studies have focused on enhancing oxidative stability of frying oils by effective natural antioxidants especially those derived from plants such as phenolic components. Leaves of Moringa oleifera (ML) and Ziziphus Lotus (JL) are a good example of parts of a plant rich in polyphenols. In this study, ML and JL extracts were compared for their phenolic contents, antioxidant activity and their effects on the thermal stability of corn oil (CO). Refined CO and CO supplemented with ML (CO+ML) and JL (CO+JL) were exposed to heating (180 °C) for 8 h. Changes in peroxide value (PV), free fatty acid (FFA) content, oxidative stability (OS) and fatty acids (FAs) profiles were monitored. Results showed that JL contained higher phenolic contents than ML. Phenolic compounds included phenolic acids and flavonoids. For antioxidant activities, JL exhibited greater anti-DPPH activity and had higher reducing power than ML. After heating for 8 h at 180 °C, CO+ML and CO+JL showed lower PV and FFA and higher OS than CO. CO+JL was more stable than CO+ML. For FAs profile, significant increases in saturated and mono-unsaturated FAs percentages and a significant decrease in polyunsaturated were recorded for CO and CO+ML. No changes in FAs composition were observed for CO+JL which suggest that this oil resist more to oxidation. This could be attributed to the presence of polyphenols as antioxidant compounds allowing extended oil thermal resistance.