Optimization extraction, structural features and antitumor activity of polysaccharides from Z. jujuba cv. Ruoqiangzao seeds

As a discarded byproduct of jujube ( Z . jujuba ), its seeds contain various biological components. Response surface methodology was used to optimize ultrasound-assisted heating extraction conditions of polysaccharides from Z . jujuba cv . Ruoqiangzao seeds (ZJSPs). The optimal parameters were as follows: temperature 83.1 °C, time 100 min, ultrasonic power 140 W, and water-material ratio 33.5 mL/g, allowed a maximum yield of 1.97%. One main fraction (ZJSPs-1) was successfully purified by ion-exchange and gel-permeation chromatography. With a molecular weight of 342 kDa, ZJSPs-1 was composed of arabinose, glucose, xylose, galactose and rhamnose. The presence of pyranose-form sugars as well as both α- and β-configurations was validated by FT-IR and 1 H NMR. TG/DSC indicated that ZJSPs-1 has a favorable thermal stability. XRD suggested that ZJSPs-1 exhibited both crystalline and amorphous portions. ZJSPs-1 was in aggregates of homogenous-dense honeycomb like structures observed by SEM and AFM. ZJSPs-1 possessed antitumor activities against HeLa cells in a dose- and time-dependent manner at 24 and 48 h with IC 50 of 164.6 and 87.1 μg/mL, respectively. Fluorescent microscopic and flow cytometry revealed that ZJSPs-1 inhibited the proliferation of HeLa cells through apoptosis. Z . jujuba seeds are good sources for antitumor polysaccharides in pharmaceutical and food industries.