Microwave-assisted extraction (MAE)MAE was performed in the closed vessel unit MDS2002 (Xin’yi Microwave Extraction Instrument Company, Shanghai). This unit is equipped with temperature
sensor. Maximum oven power for this system is
800 W. For the first series of experiments 3 g of the whole
dried and ground material were placed in 100 ml PFTE
(CEM) extraction vessels and appropriate amount of solvent
was added (30 or 75 ml). Then the container was
lidded and a temperature sensor would be inserted into
the container to measure and control the internal temperature,
which allows technical parameters of instrumentation
used in order to prevent overheating (the exact
temperature was detected by sensor, and the temperature
was ramped up step by step, generally 2–5 C increased
every time. When the temperature was just 2–3 C under
the desired temperature, a program for heating preservation
was started, under which the controller maintained
temperature to ±1 C and shut the heating device off
when the set point was reached). The pressure was preestablished
at a safe limit and the pressure profile was
recorded and would not go beyond the limit during
extraction run. The extraction was performed for a few
minutes on a definite power. The extraction temperature
was set at different degrees due to different solvents and
programmed as follows: ramp to the temperature for
5 min step by step, hold at temperature for a few minutes.
Microwave power was 800 W (100%). After extraction,
the vessels were left for 30 min to cool down below
35 C. Then each extract was filtered through filter paper
and evaporated to dryness.