Objective   A subcritical water extraction method was optimized by response surface experiments to extract polysaccharides from pitaya stems.

  Method  On the basis of a single factor test, pitaya stems were extracted using phenol-sulfuric acid to determine the polysaccharide content. To optimize the subcritical water extraction process assisted by ultrasonic pretreatment, water temperature, extraction time, liquid-to-material ratio, and pH were used against polysaccharide extraction rate in a response surface experiment.

  Result  The optimized processing conditions included the applications of water at pH 5.9 and 144 ℃ with a liquid-to-material ratio of 31:1 (mL:g) to extract for 19 m. A polysaccharide extraction rate of 26.47% was achieved.

  Conclusion  The established method appeared adequate for polysaccharide extraction from pitaya stems, and the mathematical model obtained be used to analyze and predict the process parameters.