The effect of ultrasound assisted extraction on structural composition, antioxidant activity and immunoregulation of polysaccharides from Ziziphus jujuba Mill var. spinosa seeds

In this study, the polysaccharide was extracted from Ziziphus jujuba Mill var. spinosa seeds (ZSS) with ultrasound assisted extraction method (UAE). Box-Behnken design (BBD) and response surface methodology (RSM) were applied to obtain the optimal conditions for perfect yield of ZSS polysaccharide: extraction temperature 52.5 degrees C, extraction time 21.2 min, extraction power 134.9 W and ratio of liquid to solid 26.3 mL/g. The yield was 1.05 +/- 0.08%, which roughly equated to that 0.93 +/- 0.14% of 6 h heating water extraction (HWE). The results illustrated that the polysaccharide extracts by UAE and HWE exhibited obvious difference in chemical structure, including morphological traits, optical rotation, monosaccharides composition, molecular distribution, and Fourier transform infrared spectroscopy (FT-IR) spectra. The two polysaccharide extracts both showed certain antioxidant activities, including scavenging ABTs radical, superoxide radical, hydroxyl radical and Ferrous ion in vitro and inhibiting reactive oxygen species (ROS) accumulation in PC12 cells. Compared with HWE extract, UAE extract scavenged more hydroxyl radical and Ferrous ion in the same concentration (1 and 2 mg/mL). Moreover, the UAE extract exerted significantly stronger effect on inducing Cyclooxygenase-2 (COX-2) expression in RAW264.7 macrophages than HWE extract. In conclusion, UAE could be used as an efficient technique for extracting ZSS polysaccharide.