Table 1. Comparison of Different Extraction Methods of FA.

method	principle	equipment	time	advantages	disadvantages
alkali-soluble acid precipitation23,24	solubility differences	conventional extractor	5–6 h	easy to operate	time-consuming
					low extraction yield
					high content of impurities
chemical degradation25,26	oxidation increases acid solubility	conventional extractor	36–72 h	high yielding	time-consuming
					expensive
ultrasound-assisted27	ultrasound energy	ultrasonic water bath	1 h	rapid	lower efficiency than the microwave method
					range of ultrasonic action is narrow
microwave-assisted28	microwave energy	microwave extractor	10–20 min	very rapid	difficult to industrialize