Ultrasonic enzyme-assisted extraction of comfrey (Symphytum officinale L.) polysaccharides and their digestion and fermentation behaviors in vitro

This study aimed to explore the optimum conditions for the ultrasonic-enzyme-assisted extraction of comfrey (Symphytum officinale L.) polysaccharides (SOP) by the response surface methodology (RSM). The optimum extraction conditions included an extraction time of 62 min, an enzyme complex dose of 1.1 %, a liquid-to-solid ratio of 21 mL/g, and a pH value of 6. A SOP yield of 20.32 % was achieved. The digestion and fermentation behaviors of SOP in vitro were determined. A digestion test was performed in simulated gastric fluid (SGF) and simulated intestinal fluid (SIF). A fermentation model was prepared with the cecal contents of chickens. The results showed that SGF (2.15 ± 0.09 %) and SIF (1.08 ± 0.06 %) were ineffective in the digestion of SOP. During fermentation, the pH values of the culture medium were lower than the initial pH (7.75 ± 0.03). SOP (47.06 ± 1.79 %) was used by the chicken cecal microbiota, which produced 34.12 ± 0.79 mg/mL short-chain fatty acids at 48 h. Moreover, the composition of the chicken cecal microbiota could be regulated by SOP during fermentation. The relative abundance of Lactobacillus at the genus level was improved. Therefore, SOP might have the potential to serve as a prebiotic in chicken production.