Effects of air temperature and blanching pre-treatment on phytochemical content, antioxidant activity and enzyme inhibition activities of Thai basil leaves (Ocimum basilicum var. thyrsiflorum)

Thai basil leaves (Ocimum basilicum var. thyrsiflorum) have been used in food flavoring and traditional medicine. Hot-air drying is a convenient and low-cost method to preserve them for long-term use but causes the loss of their bioactive compounds during the process. In this work, the effect of pre-blanching on preserving these characteristics of Thai basil leaves dried at different air temperatures was studied. The antioxidant characteristics were evaluated by the contents of total phenolics, total flavonoids and total chlorophylls and the scavenging capacity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals. In addition, the inhibitory activities against starch-digesting enzymes were assessed with α-amylase and amyloglucosidase. At the air temperature of 50oC, antioxidant characteristics of dried leaves with pre-blanching were proven better than those without blanching and came close to those of the fresh sample. The drying temperature had more evident effects on inhibitory activities against starch-digesting enzymes than blanching. These activities of hot-air dried leaves were comparable to those of the fresh one. This study could provide insights into the integration of blanching and hot-air drying to preserve medicinal plants.