Determination of total phenolic content
1.5 g of each sample was transferred to centrifuge tubes and 85% methanol (25 ml) added and the mixture put in a shaker for 30 min to ensure uniform mixing. Then, the methanol layer in each tube was separated by centrifugation at 10000 g for 10 min. The solvent supernatant was transferred to a 50 ml falcon tube. The residue was again mixed with 15 ml methanol and centrifuged as described above. The supernatant was separated as previously described and mixed with the former supernatant. The tube containing supernatant was adjusted to 50 ml using methanol. The extracted solution was kept in 0°C until analysis (Sompong et al., 2011).