Ultrasonic-assisted extraction of polysaccharide from Dendrobium officinale: Kinetics, thermodynamics and optimization

Dendrobium officinale polysaccharide (DOP) was extracted from Dendrobium officinale by ultrasonic-assisted hot water extraction (UHWE). Its characterizations were analyzed by scanning electron microscope (SEM), Fourier Transform infrared spectroscopy (FT-IR) and Ultra performance liquid chromatography-mass spectrometry (UPLC-MS). Then the Box-Behnken design (BBD) of response surface method (RSM) was used to optimize the operating conditions firstly. Finally, a kinetic model for the process of extracting DOP was established according to the Fick’s second law, thermodynamic characteristics were investigated, and the other optimal operating condition was obtained. The results showed DOP was a network with small bubble-like pores and irregularly aggregated heteropolysaccharide mainly composed of Man, Glc, Ara, and a trace of Gal in a molar ratio of 50.89:30.17:4.78:1. A high linear correlation (R2 ≥ 0.9) indicated the extraction process matched well with the Fick’s second law of diffusion. Thermodynamic studies showed that the extraction process was endergonic and not spontaneous. The final optimal condition, 353.15 K, 60:1 mL/g and 60% for 150 min with low energy consumption, high mass transfer and high yield, was obtained by comparison.