Phenolic compounds from Citrus leaves: Antioxidant activity and enzymatic browning inhibition

Phenolic compounds from Citrus are known to be a topic of many studies due to their biological properties including antioxidant activity. Methanolic and aqueous extracts were isolated from Citrus leaves of different species (C. clementina, C. limon, C. hamlin, C. navel, C. aurantifolia, C. aurantium and C. grandis) harvested in Algeria. The results showed that aqueous extracts of all species are rich in total phenolic compounds and flavonoids (from 68.23 to 125.28mg GAE/g DM) and (from 11.99 to 46.25mg QE/g DM) respectively. The methanolic and aqueous extracts were examined for in vitro antioxidant properties using various antioxidant assays. For aqueous extracts, C. limon showed an important DPPH radical scavenging activity (IC50 35.35μg/mL), and C. clementina exerted the highest ABTS radical scavenging activity (1,174.43μM ET/g DM) and a significant ferric reducing potential (30.60mg BHAE/g DM). For methanolic extracts, C. clementina showed the highest antioxidant activity for all the realized assays (IC50 41.85μg/mL, 378.63μM ET/g DM and 13.85mg BHAE/g DM) for DPPH, ABTS radicals scavenging activities and ferric reducing potential respectively. Antiperoxidase and antipolyphenol oxidase activities of these samples were also evaluated. In this investigation, the assessment of antiperoxidase activity proved that the leaves extracts of different species were able to inhibit peroxidase activity. However, this inhibition varied with the species and the source of these enzymes. On the other hand, the aqueous extracts of different species showed moderate inhibition of polyphenol oxidase, while no effect on these enzymes was obtained with methanolic extracts.