Abstract
The antioxidant activity of several Malaysian plant extracts was analyzed simultaneously with their pro-oxidant capacity. This ratio represents an index (ProAntidex) of the net free radical scavenging ability of whole plant extracts. We observed that ethanolic extracts of Nephelium lappaceum peel, Fragaria x ananassa leaf, Lawsonia inermis leaf, Syzygium aqueum leaf and grape seed had a lower Pro-Antidex than the commercially available Emblica™ extract which is an antioxidant agent with very low pro-oxidant activity. Among the aqueous extracts, Lawsonia inermis leaf, Nephelium mutobile leaf and grape seed had lower pro-oxidant activity compared to the Emblica™ extract. Among these extracts, aqueous extract of Nephelium mutobile leaf had a very low index of 0.05 compared to 0.69 for Emblica™. Most of the extracts had a far lower ProAntidex compared to the Vitamin C. The index enables us to identify extracts with high net free radical scavenging activity potential. The ProAntidex is beneficial as a screening parameter to the food industries and healthcare.
Highlights
Antioxidants are substances that protect other chemicals in the body from damaging oxidation reactions by reacting with free radicals and other reactive oxygen species within the body, hindering the process of oxidation [1]
The pro-oxidant and antioxidant effect of plant extracts are due to the balance of two activities: free radical-scavenging activity and reducing power on iron ions, which may drive the Fenton reaction via reduction of iron ions
High concentrations of antioxidants may have pro-oxidant activity. This can be best seen in the case of ascorbic acid, which is a well known pro-oxidant at very high concentrations [9]. This occurs as a result of the predominance of reducing power over its free radical scavenging activity
Summary
Antioxidants are substances that protect other chemicals in the body from damaging oxidation reactions by reacting with free radicals and other reactive oxygen species within the body, hindering the process of oxidation [1]. Studies have revealed pro-oxidant effects of antioxidant vitamins and several classes of plant-derived polyphenols such as flavonoids [4], tannins [5] and curcumin [6]. The pro-oxidant and antioxidant effect of plant extracts are due to the balance of two activities: free radical-scavenging activity and reducing power on iron ions, which may drive the Fenton reaction via reduction of iron ions. A predominant reducing power (on iron ions) over the free radicalscavenging activity in a mixture of compounds results in the pro-oxidant effect [8]. The pro-oxidant capacity of the extracts were compared to the IC50 (mg/mL) of the antioxidant scavenging activity of DPPH radical. This ratio of pro-oxidant/antioxidant activity enabled us to evaluate the net antioxidant capacity of the extracts as this index will include the effective free radicalscavenging ability, taking into account pro-oxidant effect of the extracts
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