Ultrasonic Extraction of Polysaccharides from Dendrobium officinale Leaf: Kinetics, In Vitro Activities, and Characterization

This study explored the kinetics of ultrasonic extraction of polysaccharides (<i>DO</i>LP) from <i>Dendrobium officinale</i> leaf (<i>DO</i>L), evaluated the in vitro bioactivity of <i>DO</i>L extracts and <i>DO</i>LP, and characterized the <i>DO</i>LP. A kinetic model was developed based on Fick's second law. A technique utilizing 400 W for 50 min was employed for the ultrasonic extraction of <i>DO</i>LP, with an optimal solid-liquid ratio established at 1:40 (g/mL). <i>DO</i>L extracts dried using different methods exhibited varying antioxidant activity and inhibitory effects against α-amylase and α-glucosidase. An in vitro study revealed that <i>DO</i>L extracts obtained through vacuum freeze drying demonstrated significantly stronger antioxidant activity, while those derived through microwave drying showed superior inhibitory effects against α-amylase and α-glucosidase compared to the other two drying methods. Furthermore, it was observed that the in vitro bioactivity of <i>DO</i>LP (purity: 74.07 ± 0.52%) was significantly lower than that of <i>DO</i>L extracts. Nevertheless, <i>DO</i>LP (5.0 mg/mL) demonstrated a scavenging ability reaching 64.86% of VC for DPPH radical and 67.14% of VC for ·OH radical, and the inhibition of <i>DO</i>LP (10 mg/mL) on α-amylase and α-glucosidase reached 58.40% and 38.28% of the acarbose, respectively. The findings revealed that <i>DO</i>LP are predominantly composed of mannose, glucose, galactose, and arabinose in a distinctive molar ratio of 89.00:16.33:4.78:1.