2.4. Determination of total phenolic content (TPC)
The determination of TPCs of the extract and powder was
conducted using the procedure described by Singleton et al.[15].
Sample solution (0.1 mL) was first transferred to a container,
followed by the addition of 7.9 mL of DI water and 0.5 mL of Folin
Ciocalteu’s reagent. Na2CO3 (1.5 mL; 20% w/w) was then added
into the same container to make a total volume of 10 mL. The container was kept in the dark for two hours and the reaction allowed
to proceed at a basic pH. The absorbance was read using a UV–Vis
spectrophotometer (Cary 50 by Agilent Technologies, U.S.A.) at a
wavelength of 765 nm. Gallic acid solution was used as positive
control, and the TPC was expressed as mg GAE/g of material.