The extraction experiment was designed as follows:extraction solution (water, water + sodium hydroxide and water + sodium hydroxide + ultrasound), extraction temperature (20, 40, 60, 80 and 100 C), extraction time (1, 2, 3,4 and 5 h) and extraction frequency (1, 2, 3 and 4). Additionally, the concentration of sodium hydroxide(5–30 g ⁄l) and length of time of the ultrasound (5–25 min) used in the extraction were also considered in the design of the experiment.
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