Effect of ohmic pretreatment on tissue integrity and extraction yield of Chinese chives (Allium tuberosum) leaf oil

Abstract

Chinese chives (Allium tuberosum Rottl.) are known for its antimicrobial and antioxidant properties. However, extract from Chinese chives was not commercially available due to very low extraction yield of the conventional method, steam distillation. This study focused on effect of ohmic pretreatment at different electric field strengths on tissue integrity and extraction yield of Chinese chives leaf oil. The field strength was varied at E = 0, 25, 50, 75 and 100 V/cm. For all treatment, the cut-off temperature was fixed at 60 °C. The tissue integrity was determined by an electrical conductivity disintegration index (Z) and viable staining using neutral red dye. It was found that as the field strength increased, Z value increased indicating a higher degree of tissue damage. The highest degree of tissue damage (Z ~ 0.8) was obtained when E > 75 V/cm were applied. The viability test showed agreeable results to the Z values. More red cells were observed at the lower field strength. At E = 25 v/cm, the amount of viable cells were comparable to the control (fresh tissue) while there was almost no viable cell left at E > 75 V/cm. When ohmic pretreatment at E = 75 V/cm was applied prior to 2.5 h of steam distillation, the extraction yield was increased from 0.12+0.01% to 0.16+0.02% by fresh leaf weight or about 33%. Thus, ohmic pretreatment was suggested to increase the permeability of any biological materials prior to extraction process in order to enhance the extraction yield.