Ohmic heating-assisted water extraction of steviol glycosides and phytochemicals from Stevia rebaudiana leaves

Abstract

Stevia rebaudiana leaves are a good source of sweetening compounds and phytochemicals. The effect of ohmic heating-assisted water extraction (OH-AWE) was investigated on the extraction of steviol glycosides (stevioside and rebaudioside A) and phytochemicals of S. rebaudiana leaves. Moisture content (MC) of the leaves was adjusted to 20, 30 and 40% (wet basis) and three electric field strengths (E) (75, 150 and 200 Vcm−1) were applied under ohmic heating (OH) to assist water extraction. Untreated leaves extracted by water (UN–W) and methanol (UN-M) served as the control and conventional method, respectively. Results indicated that OH-AWE gave higher stevioside content (11.48–15.34 g/100g dry weight (DW)), rebaudioside A (6.53–8.58 g/100g DW) and total flavonoid content than UN-W and UN-M. Highest chlorogenic, syringic, caffeic and ferulic acids, and total phenolic contents were obtained from OH-AWE of leaves containing 30% (200 Vcm−1) and 40%MC (150 Vcm−1). OH-AWE also gave the highest concentration of stevioside and rebaudioside A in extract powder and optimal extraction yields compared with UN-W and UN-M. Results suggested OH-AWE as a potential extraction method for preparing sweetening agents containing high phytochemicals.