HPLC determined product concentration. A 500 μL sample was taken and mixed thoroughly with the same amount of absolute ethanol by vortexing 30 s. The sample was centrifuged at 8000 × g for 10 min and filtered with a 0.2 µm PES membrane filter (Jinteng, Tianjin, China).
The concentrations of raspberry ketone and p-coumaric acid were measured by high-performance liquid chromatography (HPLC, LC 20A LabSolutions, Shimadzu Corp., Kyoto, Japan) with an Agilent Extend-C18 3.5 μm column (4.6 × 250 mm). The column was at 35 °C, and a flow rate of 0.5 ml/min was used. Mobile phase A (65%) was water with 0.1% (v/v) formic acid; mobile phase B (35%) was acetonitrile. Raspberry ketone and p-coumaric acid were detected via DAD detection. The raspberry ketone was detected at 222 nm, p-coumaric acid was detected at 305 nm.
The concentrations of raspberry ketone and p-coumaric acid were measured by high-performance liquid chromatography (HPLC, LC 20A LabSolutions, Shimadzu Corp., Kyoto, Japan) with an Agilent Extend-C18 3.5 μm column (4.6 × 250 mm). The column was at 35 °C, and a flow rate of 0.5 ml/min was used. Mobile phase A (65%) was water with 0.1% (v/v) formic acid; mobile phase B (35%) was acetonitrile. Raspberry ketone and p-coumaric acid were detected via DAD detection. The raspberry ketone was detected at 222 nm, p-coumaric acid was detected at 305 nm.