Polysaccharide extraction optimization, monosaccharide composition, and antioxidant activity analysis of different varieties of Gastrodia elata Bl aerial parts

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Abstract
This study investigates the optimal extraction conditions, monosaccharide composition, and antioxidant activity analysis of polysaccharides from the aerial parts of three different varietal varieties of Gastrodia (i.e., G. elata Bl. F. elata, G. elata Bl. F. Viridls MaKino, and G. elata Bl. F. Glauca S Chow). The influence of extraction temperature (30–70 °C), extraction time (15–55 min), and liquid-to-solid ratio (25–65 mL/g) on the yield of polysaccharides was analyzed through single-factor experiments. The response surface methodology was used to optimize the extraction process, and a mathematical model was established to obtain the optimal extraction conditions. The response surface experiment was presented as follows: The optimal extraction conditions for polysaccharides were a liquid-to-solid ratio of 59 mL/g, 56 °C, and 36 min. The polysaccharide yield in G. elata. Bl. F. Glauca S Chow aerial parts under these conditions was 10.90%, which was close to the theoretical value calculated by the model (10.64%). Under the optimal conditions, the yields of polysaccharides followed: G. elata Bl. F. elata (11.32%) > G. elata Bl. F. Glauca S Chow (10.90%) > G. elata Bl. F. Viridls MalKino (10.50%). The polysaccharides were mainly composed of 10 monosaccharides, including glucose, rhamnose, mannose, and xylose. However, the content of monosaccharides in polysaccharides of different varieties of Gastrodia elata Bl aerial parts varied greatly, with glucose and rhamnose being the highest, both exceeding 20%. The polysaccharides in different varieties of Gastrodia elata Bl aerial parts had certain in vitro antioxidant activity. The total reducing power and scavenging rates of 2,2-diphenylpicrylhydrazyl (DPPH) and 2,2′-azinobis-(3-ethylbenzthiazolin-6-sulfonic acid) (ABTS) free radicals increased with the increase of polysaccharide concentration. When the polysaccharide concentration was 1.0 mg/mL, the scavenging rates of DPPH and ABTS free radicals were both over 80%. This study provides a theoretical basis for the further development and utilization of Gastrodia elata Bl aerial part resources. Graphical Abstract Using ultrasound-assisted extraction and response surface methodology to optimize the extraction of polysaccharides from the aerial parts of Gastrodia elata, polysaccharide yields of three different G. elata varieties were all above 10%, and the extracted polysaccharides were composed of 10 monosaccharides, including glucose and galactose, and exhibited good in vitro antioxidant activity.

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