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University of the Aegena (2018)

Extraction of antioxidant polyphenols from Moringa oleifera leaves using a biomelecule based low transition temperature mixture

Καραγεώργου, Ιωάννα

Titre : Extraction of antioxidant polyphenols from Moringa oleifera leaves using a biomelecule based low transition temperature mixture

Auteur : Καραγεώργου, Ιωάννα

Etablissement de soutenance : University of the Aegena

Grade : Doctor of Philosophy (PhD) 2018

Résumé
M. oleifera is native tree found in the Himalayan, widely known because of its significant nutritional and pharmacological properties. In this study, for the first time M. oleifera tree was cultivated in Greece and was studied for its nutrition value. In M.ο leaves was found high concentration of proteins, amino acids total phenols and flavonols. It is considered a rich source of lipids, ash, minerals, carotenoids, and vitamins C and E. The herbal tea was high in total phenols and flavonols. Subsequently, the extraction of polyphenols from M. oleifera leaves was investigated, using a biomolecule-based low-transition temperature mixture (LTTM). The first step was to optimise LTTM concentration (CLTTM) the molar ratio (Rmol) of glycerol-to-sodium acetate and to assess the effect of temperature. A maximum yield in total polyphenols was achieved using a CLTTM = 80% (w/v) and a Rmol = 6 while, in a comparative evaluation using 80% ethanol showed that the LTTM used was significantly more efficient in extracting polyphenols and flavonoids, yielding extracts with higher reducing power. These newly synthesized LTTM with optimized composition were used to evaluate the effect of β-cyclodextrin (CD) on the efficiency of polyphenol extraction from M. oleifera leaves (MoL). The process developed to assess the simultaneous effect of CD concentration (CCD), liquid-to-solid ratio (RL/S) and temperature (T). Under optimized conditions (CCD = 1%, RL/S = 40 mL g-1, T = 40 °C), the yield in total polyphenols (YTP) was 67.18±5.04mg GAE g-1 DW. This value was significantly higher than that determined for the extraction performed with LTTM alone or 80% aqueous ethanol. The extraction rate was slowed down in the presence of CD, yet the higher extraction capacity of the LTTM/CD medium was confirmed but demonstrated that there was no selective extraction of any particular polyphenol, suggesting that CD acted merely as an extraction booster. Polyphenol-containing extracts from MoL were obtained using LTTM and a combination of LTTM/CD were stored at various temperatures for a period of 18 days. The antiradical activity (AAR) displayed a constant decline while, the presence of HP-β-CD, slow down this progression decline. The use of liquid chromatography-diode array-mass spectrometry showed that after storage for 18 days at 50 °C, the major quercetin glycosides occurring in MoL suffered extended degradation.

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