*2.6. Resveratrol Quantification*

An exactly 0.5 mL sample was mixed with 0.5 mL polydatin (internal standard, 50 μM) in methanol and then added into 4 mL methanol under vortexing for 60 s. After the mixture was centrifuged at 15,000× *g* for 60 min, the supernatant was measured on the Alliance HPLC system equipped with a 2695 separation module and 2998 PDA detector (Waters, Milford, MA, USA). The mobile phase was a mixture of methanol and distilled water (50:50, *v*/*v*), the flow rate was 1 mL min−1, and the column temperature was 35 ◦C. Both *trans*-resveratrol and polydatin were analyzed at 306 nm [23].
