Ultrasound-assisted extraction of antioxidants from manuka leaves

Abstract

The current study involves the ultrasound-assisted extraction of Leptospermum scoparium (manuka) leaves to maximize the antioxidant activity. The effects of four extraction parameters (ethanol concentration 0-100%, time 540 min, temperature 30-70°C, and amplitude 42-210 micrometer) on antioxidant content were studied based on single factor design. This is achieved by changing one factor at a time while keeping other variables constant (50% eth anol concentration, 10 min, 50°C, 168 m, and 50 ml solvent). The antioxidant activity was determined using 1,1 diphenyl-2-picrylhydrazyl (DPPH) and expressed in percentage of radical scavenging activity (RSA). The extractions were carried out by using a 200 W ultrasonic processor (24 kHz) with a 3 mm diameter sonotrode. The statistical analysis indicated that all the studied parameters had significant effects (P<0.0001) on antioxidant content. The highest antioxidant content was achieved using 50% ethanol: water solvent (82.28%2.03,) compared to a 100% ethanol (43.38%4.04) or water (24.77%+-4.36). The ultrasound technology allowed for a faster extraction time, the results demonstrated an increase of RSA from 62.78%+-2.06 (5 min) to 78.68%2.07 after 10 minutes of extraction. In addition, the sonification amplitude which corresponds to the energy density was also found to increase the antioxidant content. Extraction at higher amplitude setting (>168 µm, 0.52 W/ml) increased the antioxidant RSA from 60.78%1.54 to 81.69%+-2.14 when compared to lower amplitude of 42 µm (energy density 0.13 W/ml). This may be explained by higher cavitation rate that occurs when higher amplitude was used which allowed for greater penetration of solvent into the cell walls, thus effectively releasing the intracellular compounds of the plant1 . In regards to temperature, higher RSA was also observed at 50° C (56.05%+-5.14), while the activity decreased significantly at lower and higher temperatures. Based on the results, it is concluded that ultrasoundassisted extraction significantly influences the antioxidant content of Leptospermum scoparium ethanol extracts.