Optimization of Essential Oil Extraction from Bitter Leaf (Vernonia Amygdalina) by Using an Ultrasonic Method and Response Surface Methodology

Table 1

Codes and levels of independent variables used in the response surface methodology (RSM) design.

Symbol	Independent variables	Coded levels
		Low (−1)	Middle (0)	High (+1)
A	Ultrasonic power (W)	100	150	200
B	Sonication time (min)	10	20	30
C	Liquid-solid ratio (ml/g)	4	6	8