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

Abstract

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.

Keywords: Dendrobium officinale leaf; characterization; in vitro bioactivity; polysaccharide; ultrasonic extraction.

Figure 1

DOLP yield under different solid−liquid ratios (A); Relationship between ln[C_∞/(C_∞ − C)] and ultrasonic extraction time at different ultrasonic power levels (B); Relationship between (C_∞ − C)/C_∞ and ultrasonic time at different ultrasonic power levels (C); Relationship between t_1/2 and ultrasonic power (D); Relationship between 10⁴D_u and ultrasonic power (E); DOL extracts by MD (F(a)), HAD (F(b)), VFD (F(c)), and DOLP by VFD (F(d)). Different lowercase letters in Figure 1A indicate significant differences (p < 0.05).

Figure 2

In vitro activity of DOLP. DPPH radical scavenging activity (A); ABTS radical scavenging activity (B); Hydroxyl radical-scavenging activity (C); Ferrous reducing power (D); α-amylase inhibitory activity (E); α-glucosidase inhibitory activity (F). Different lowercase letters indicate significant differences (p < 0.05) at the same concentration.

Figure 3

Heat maps of Pearson correlation analysis: before (A) and after purification (B); * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001.

Figure 4

UV spectrum of DOLP (A); FT−IR spectrum of DOLP (B); Ion chromatography to determine the monosaccharide compositions of monosaccharide standards (C); DOLP (D).