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

This study explored the kinetics of ultrasonic extraction of polysaccharides (DOLP) from Dendrobium officinale leaf (DOL), evaluated the in vitro bioactivity of DOL extracts and DOLP, and characterized the DOLP. 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 DOLP, with an optimal solid–liquid ratio established at 1:40 (g/mL). DOL extracts dried using different methods exhibited varying antioxidant activity and inhibitory effects against α-amylase and α-glucosidase. An in vitro study revealed that DOL 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 DOLP (purity: 74.07 ± 0.52%) was significantly lower than that of DOL extracts. Nevertheless, DOLP (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 DOLP (10 mg/mL) on α-amylase and α-glucosidase reached 58.40% and 38.28% of the acarbose, respectively. The findings revealed that DOLP are predominantly composed of mannose, glucose, galactose, and arabinose in a distinctive molar ratio of 89.00:16.33:4.78:1.