Effect of heat on the total phenolic content and <i>in vitro</i> antioxidant properties of the methanolic leaf extract of <i>Moringa oleifera</i>

Abstract

Background: Moringa oleifera provides natural dietary sources of antioxidants (vitamins, carotenoids, phenolic compounds) that protect against free radical oxidation damages. The plant is usually cooked or steamed before eating and which consequently, results in changes of nutritional and chemical composition of important phyto-components.
Objective: This study assessed the effect of heat on the total phenolic content and in vitro antioxidant properties of the methanolic leaf extract of Moringa oleifera leaves
Methods: Methanolic leaf extracts of heat treated and untreated leaves of M. oleifera were prepared and an in vitro 3+total phenolic content (TPC), ferric ions (Fe ) reducing anti-oxidant power (FRAP) and total antioxidant activity 3 3 3(T AA) evaluations were carried out for both unheated and heated samples at 100 µg/cm, 50µg/cm and 25 µg/cm, respectively.
Results: The TAA results showed a minimum of 50% decrease in the untreated over the heated extracts while TPC and FRAP showed a maximum decrement of less than 30% across all extracts concentrations of the unheated over the heated; with extract concentration-dependency only shown in FRAP.
Conclusion: Heating reduced the antioxidant functions of M. oleifera leaves by more than half without a corresponding proportionate decrement in its phenolic content or its reducing capacity. It is important to be cautious when heating the leaves of Moringa oleifera for  if one is to obtain the highest possible benefits from the bioactive, antioxidative phyto-compounds present in them.

Keywords: Moringa oleifera leaves, phyto-chemicals, heating, phenolic content, antioxidant capacity