The In Vitro Antioxidant Activity and Phytochemicals of Locally Consumed Plant Foods from Quezon Province, Philippines

Background. Quezon province has been one of the primary agricultural sources of vegetables and crops in southern Luzon due to its diverse agricultural topography. Having increased dietary awareness, consumption of antioxidant-rich foods has become relevant.
Objectives. Thirteen (13) methanolic extracts of endemic Quezon plant foods were evaluated for phytochemical constituents and antioxidant potential.
Methods. The plant extracts were subjected to in vitro antioxidant assays, which include DPPH [2,2-diphenyl-1picrylhydrazyl], FRAP [Fluorescence recovery after photobleaching], metal chelation, superoxide, nitric oxide, hydroxyl radical scavenging activities and MTT [ (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)] reduction. Qualitative phytochemical analysis were also employed.
Results. P. umbellatum, locally known as kamamba and C. longa, locally known as luyang dilaw showed high antioxidant activity using DPPH and MTT assays by 82.46±0.75% and 82.35±1.79% and 78.46±0.71% and 60.97±2.60% at 66.67 ?g/mL, respectively. FRAP assay revealed a comparable reducing power with BHT (butylated hydroxytoluene) (93.61±0.56%) at 72.15 ?g/mL in C. longa (92.49±1.32%), P. umbellatum (92.38±0.64%), and Z. officinale (90.33±2.06%) (luya), but found with low metal chelating activity. The highest activity against hydroxyl radical were observed in S. edule (sayote) (34.30±1.88%), P. edulis (pasyonaryo) (33.48±1.34%) and D. philippinensis (katmon) (34.71±0.85%) at 45.5 ?g/mL. On the other hand, Z. officinale, C. esculenta (gabi), V. unguiculata (sitaw) fruit and D. philippinensis showed dual action, as antioxidant and as pro-oxidant, in Superoxide Scavenging and Nitric Oxide assays. Quezon province plant foods contain flavonoids, phenolic compounds, glycosides and coumarins and quinones which may explain their behavior as antioxidant.
Conclusion. The study revealed that different plant foods showed different capacity to scavenge particular oxidants. However, P. umbellatum and C. longa may be considered promising sources of natural antioxidants.