EFFECT OF SOLVENT-TEMPERATURE EXTRACTION CONDITIONS ON THE INITIAL ANTIOXIDANT ACTIVITY AND TOTAL PHENOLIC CONTENT OF MUITLE EXTRACTS AND THEIR DECAY UPON STORAGE AT DIFFERENT pH EFECTO DE LAS CONDICIONES DE EXTRACCI ´ ON SOLVENTE-TEMPERATURA EN LA ACTIVIDAD ANTIOXIDANTE Y CONTENIDO DE FENOLES TOTALES EN EXTRACTOS DE MUITLE Y SU P ´ ERDIDA DURANTE EL ALMACENAMIENTO A DIFERENTES VALORES DE pH

The e ect of solvent and extraction temperature on the initial antioxidant activity (AA) and total phenolic content (TPC) of Muitle (Justicia spicigera) extracts and their decay upon storage at di erent pH values was studied. Extraction with aqueous solvents, at either 25 or 60 C, produced fresh extracts (pH 7.4) with higher initial TPC and AA. Extracts were adjusted to di erent pHs displayed di erent TPC and AA decay rates upon storage. TPC had first order decay kinetics, characterized by a relatively quick constant (k1) at relatively short storage times followed by a relatively slow constant (k2) at relatively large storage times. ABTS and DPPH assays estimated di erent AA in the extracts, attributed to compatibility di erences between the bioactive species and the free radicals.