Investigation of the impact on the antioxidant capacity and Flavonoids components of different drying methods for Sophora japonica L.

Abstract

To develop the optimal drying method for the processing of Sophora japonica L., three approaches including freeze-drying, air-drying and oven drying were investigated. The water contents in dried Sophora flower samples treated using different drying methods were compared. The total amounts of Flavonoids in methanol extracts of dried Sophora flower were measured using UV-vis spectrophotometer, and the amounts of Rutin were measured using High Performance Liquid Chromatography (HPLC). The antioxidant capacity of extract of oven dried Sophora flower was determined by three different antioxidant assays, including measurement of clearance ability for DPPH, clearance ability for free hydroxyl radical and Ferric reducing antioxidant power (FRAP) assay. In our research, freeze-drying method demonstrated a minimal impact on the morphology, color, smell and other features of Sophora flower, and the freeze-dried Sophora flower reserved the highest value of total Flavonoids component amount. However, Sophora flower dried in the oven had the lowest water content and highest Rutin amount. In addition, oven dried Sophora flower could be stored easily and had less loss of the active components. Sophora flower has been demonstrated to be antioxidant in chemical reactions. In the measurement of clearance ability of DPPH, the clearance activity was positively correlated to Sophora flower extract concentration. In terms of clearance ability for free hydroxyl radical, the antioxidant capacity of Sophora flower extract increased with the increase of its concentration in the low concentration range, while after exceeding a certain concentration, clearance activity reduced with the increase of concentration. In FRAP assay, the total antioxidant capacity of Sophora flower extract first decreased as concentration increased when concentration was below 0.2 mg/mL, but then increased with the concentration after exceeding 0.2 mg/mL. In conclusion, oven drying method could be applied in the processing of Sophora flower. Sophora flower possesses good antioxidant capacity and this could be the theoretical basis for using it in the production of health products.