Phenolic Content, Antioxidant Capacity and Cytotoxicity of Whole and Fractioned Pawpaw Extracts

Pawpaw (Asimina triloba), a deciduous species of the eastern U.S., bears the largest edible fruit of all native trees. Pawpaw fruit, rich in phenolic and antioxidant components, has been also identified as a major source of anticancer acetogenins. The objective of the study was to investigate the cytotoxicity of lyophilized pawpaw extract and phenolic rich fraction.  Extracts used in this study include the whole extract (W), Fraction 2 (F2) and Fraction 5 (F5). Brine shrimp assay was used to assess toxicity of these extracts. Pawpaw pulp was extracted with 100% acetone twice, and then lyophilized. Acetonic (AcOH) extract was first made with fruit pulp of popular pawpaw cultivars, ‘PA Golden’ and NC-1, which was lyophilized and then reconstituted with double distilled water (DDH₂O), followed by fractionation with different solvents in the order of DDH₂O, 50% methanol (MeOH), 100% MeOH, 100% AcOH and 50% AcOH. Fractioned extracts were lyophilized and phenolic content (PC) and antioxidant capacity (AC) were estimated with Folin-Ciocalteu assay and ferric reducing/antioxidant power (FRAP) assay. Absorbance readings for both Folin-Ciocalteu (760 nm) and FRAP (595 nm) assays were recorded up to 2 hrs. F5 of NC-1 had the greatest PC (1189.4 gallic acid eq. ug/ sample mg) and AC (4903.3 Trolox eq. umol/ sample ml) of four pawpaw factions examined. PC and AC of F2 were much lower than those of F5 for both cultivars. Brine shrimps were subjected to five different concentrations of fractions for cytotoxicity testing, resulting in low mortality rate. The present findings suggest that these phenolic rich two pawpaw fractions do not contain high amounts of cytotoxic acetogenins.