The Effect of 1.74 and 2.3 GHz Microwave Exposure of Ailanthus Altissima Leaf Extracts on their Antioxidant Content and Activity

Abstract

Microwave (MW) irradiation in reactors with input power levels of 200-1000 W has been frequently applied for the extraction of natural compounds from vegetal material. The aim of the present research was to investigate the effect of much lower MW input powers (< 12 W) delivered through antennas into shielded enclosures on mixtures of ethanol solution-Ailanthus altissima leaves (frozen and oven-dried), at different frequencies (1.74 and 2.3 GHz) and exposure times (0.5, 1 and 3 h). The phenolic content and antioxidant activity were quantified after the exposures. Significant differences between the antioxidant content/ activity and the type of raw material were found, in favour of frozen samples. After MW treatment, the bioactive content and activity increased in frozen Ailanthus leaf extracts compared to control. No significant effect was observed in case of extracts prepared from oven-dried samples at 60°C. The ATR-FTIR analysis indicates no significant structural changes after the irradiation. These results revealed a better extractability of phenolic compounds following MW exposure in particular at 2.3 GHz.