Analysis of total phenolic contents followed the spectrophotometric method using Folin–Ciocalteu reagent [20] following modification of a previous procedure [21] . Extraction of GP was also conducted following modification of a previously described method. Each powder sample was added to 10 mL of 80% methyl alcohol, and extraction was conducted with sonication for 2 h at 40°C. Resultant solutions were centrifuged at 4,000 × g for 20 min, and then the last supernatant was used for study.
An aliquot of 0.1 mL of each extract was added to 1.5 mL of Folin–Ciocalteu reagent (Sigma-Aldrich, USA) and diluted with a 10 times amount of distilled water, followed by equilibration for 5 min at room temperature. Then, 1.5 mL of a 6% sodium carbonate solution was added to each sample, followed by incubation for 90 min at room temperature. Finally, the absorbance value was measured spectrophotometrically at 765 nm. Total phenolic contents of GP were quantified using a gallic acid (Samchun Pure Chemicals, Co., Ltd., Korea) standard curve and expressed as micrograms of gallic acid equivalents per g-dry weight (μg GAE/g-dw).
An aliquot of 0.1 mL of each extract was added to 1.5 mL of Folin–Ciocalteu reagent (Sigma-Aldrich, USA) and diluted with a 10 times amount of distilled water, followed by equilibration for 5 min at room temperature. Then, 1.5 mL of a 6% sodium carbonate solution was added to each sample, followed by incubation for 90 min at room temperature. Finally, the absorbance value was measured spectrophotometrically at 765 nm. Total phenolic contents of GP were quantified using a gallic acid (Samchun Pure Chemicals, Co., Ltd., Korea) standard curve and expressed as micrograms of gallic acid equivalents per g-dry weight (μg GAE/g-dw).