Determination of Total Phenolic Content. The total phenolic
content (TPC) of the extract was estimated using a method by Wang
et al.32 Briefly, 25 μL of gallic acid standard or purple tomato extract was
mixed with 125 μL of FolinCiocalteu reagent in 96-well microplates
and allowed to react for 10 min at room temperature. Then 125 μL of
saturated sodium carbonate (Na2CO3) solution was added and allowed
to stand for 30 min at room temperature before the absorbance of the
reaction mixture was read at 765 nm using a visible-UV microplate
kinetic reader (EL 340, Bio-Tek Instruments Inc., Winooski, VT,
USA).32 The results were expressed in milligrams of gallic acid equivalent
per gram of dry weight (mg GAE/g DW). All samples were tested in
triplicate.
Antioxidant Assays. Photochemiluminescence (PCL) Assay.