Determination of total phenolic content
The total phenolic compound in plant extract was determined by
Folin-Ciocalteu reagent (Javanmardi et al., 2003). The phenolic
compound was oxidized to phenolates by the reagent at alkaline pH
in a saturated solution of sodium carbonate, resulting in a blue
molybdenum-tungsten complex that was detected at 764 nm. Fifty
μl of plant extract were mixed with 2.5 ml of Folin-Ciocalteu’s
reagent diluted at 1/10, and 2.0 ml of sodium carbonate (7.5%,
w/v). Then, the sample was incubated at 45°C for 15 min until the
blue color was developed. The total phenolic content was
calculated by comparing to standard gallic acid and expressed as
milligrams of gallic acid equivalents to one gram of extract (mg
GAE/g extract).