Ultrasound-Assisted Extraction of Total Phenolic Compounds from Inula helenium

Table 2

Factors and levels of the orthogonal design.

Influence factors	Level
	1	2	3
(A) Ethanol concentration	20%	25%	30%
(B) Solid-liquid ratio/g/mL	1 : 15	1 : 20	1 : 25
(C) Number of extractions	1	2	3
(D) Ultrasonic time	35 min	40 min	45 min