Effects of different pretreatments on the drying and quality characteristics of Strobilanthes sarcorrhiza (C. Ling) by hot-air drying

In this study, the effects of ultrasound (USP), freeze-thaw (FTP), microwave (MWP), and blanching (BLP) pretreatments on the drying kinetic, water migration, microstructure, phytochemical compositions, and antioxidant activities of SSL were investigated. The SSL after BLP with large porous structures had higher effective moisture diffusivity and drying rate than the control with honeycomb structures, and the BLP-HAD group decreased its initial drying time and energy consumption of 51.23 % and 53.09 %, respectively. The SSL treated with BLP-HAD had improved rehydration rate of 2.23 g/g, hardness of 51.52 N, and shrinkage rate of 80 %. Additionally, the SSL after BLP treatment had higher contents of saponin (10.13 g/100 g), total phenolic (64.74 mg/100 g), and total flavonoid (3.95 g/100 g) than the HAD, thereby resulting in enhanced antioxidant activities of BLP-HAD group. BLP combined with hot-air drying is a promising pretreatment technique, as it improves both the drying process and the quality of the SSL. • Four pretreatment methods for the SSL prior to hot-air drying were evaluated. • BLP induced microstructural alterations and water redistribution of the SSL. • BLP improved drying rate and reduced energy consumption. • BLP increased saponin, total phenolic, and total flavonoid of the SSL.