Steaming and vacuum drying preserve active components, sensory and antioxidant properties of Flos Sophorae

Abstract

Flos Sophorae (FS) is medicinal and edible, while fresh FS is highly perishable. Thus, this study investigated the effects of different drying methods (hot air drying, HAD; vacuum drying, VD; freeze drying, FD) after steaming on the bioactive components and sensory quality of FS. The results indicated steaming for 1 min maximally retained the contents of total flavonoids, rutin, and quercetin in thermal drying (HAD and VD), meanwhile, the freeze-dried FS without steaming also had higher total flavonoids and rutin contents. Moreover, FD samples had the highest protein content and organoleptic properties, with closer color parameters to fresh FS, followed by the VD group. Considering comprehensively all data with processing cost, the sample of VD after steaming for 1 min was chosen to measure the antioxidant activity, which showed that FS extract was superior to Vc in ABTS• and •OH scavenging rates, and its DPPH• scavenging rate was stronger than Vc in the low concentration. These results demonstrated that vacuum drying after steaming for 1 min was suitable postharvest processing for fresh FS, which was beneficial to maintaining higher flavonoids, rutin, and sensory characteristics of FS, and its flavonoid extract had better antioxidant activity than Vc.

Keywords:
Flos Sophorae; drying; steaming; flavonoids; sensory properties