Isolation, Purification And Biological Activity Of Polysaccharide From Purple Sweet-potato

In recent years, natural polysaccharides were attracted widely concern for itsadvantages of non-toxic effects and unique biological properties, and at present, some wereused in clinically. Purple sweet-potato, consumed as both food and medicine crops herb,was generally used for anthocyanin extraction, while the residue after anthocyaninextraction was ignored. Hence, in this study, the polysaccharides from purple sweet-potato(PSPP) were extracted with ultrasonic-assisted enzymatic extraction(UEE) method and theextraction conditions of the polysaccharide were optimized with by response surfacemethodology using extraction rate as response value. The chemical structure and antioxidant,hypotensive, and antitumor activities of the purified polysaccharide were studied. Antitumormechanism was also analyzed.In this study, the extraction conditions for PSPP were optimized with Plackett-Burmandesign, steepest ascent test and Box-Benhken design using extraction rate as response valueand the optimum extraction conditions were as follows: ratio of water to raw material23.7mL·g-1, ultrasonic power207W, ultrasonic time30min, enzyme dosage60U·g-1, extractiontemperature66.6℃, extraction time1.5h, and in this case, the actual extraction rate of PSPPwas5.43%. Furthermore, SEM, FT-IR analysis and antioxidant test showed that UEEprompted bioactive polysaccharides release from purple sweet potato residue and did notcause significant changes in glycan structures.Three fractions were obtained (PSPP-Ⅰ, PSPP-Ⅱand PSPP-Ⅲ) by ion exchangecolumn and gel filtration column chromatography, and the molecular weight was33.3,17.8and75.3kDa, respectively. FT-IR and1H-NMR results showed that three fractions wereacidic polysaccharides and the monosaccharides were pyranose, which linked byβ-glycosidic bond links. Additionally, the monosaccharide composition analysis by GC-MSfound that mole ratio in PSPP-Ⅰwas rhamnose: xylose: glucose: galactose=15.96:0.91:2.43:1.00, PSPP-Ⅱ and PSPP-Ⅲ was rhamnose:galactose=2.97:1.00and rhamnose:xylose:glucose: galactose=3.51:1.92:1.44:1.00, respectively.In vitro antioxidant activities of the three kinds of polysaccharides exhibited strongantioxidant activities. PSPP-Ⅲ exhibited the highest activity of DPPH radical scavengingrate (EC50=0.388mg/mL), while the PSPP-Ⅱshowed the strongest Fe2+chelating activity(EC50=1.1mg/mL), and the reducing power; in vitro ACE effects results showed that PSPP-Ⅰ, PSPP-Ⅱ and PSPP-Ⅲ possessed excellent ACE inhibitory activities, and the IC50was 2.16,2.40and2.17mg/mL, respectively.In vitro antitumor activities of the three polysaccharides were evaluated through MTTmethod and PSPP-Ⅰexhibited the strongest anti-tumor activity(IC50=375.94μg/mL), whilepossessed little toxicity on control cells HaCat, suggesting PSPP-Ⅰ might ues as apromising anticancer polysaccharides for later use in gastric cancer therapy. Furtherresearchments found that PSPP-Ⅰcould induce human gastric cancer SGC7901cells intoearly apoptosis; SEM and TEM results showed that SGC7901cells treated with PSPP-Ⅰshrinked, cytoplasmic solid shrinkage, showing the typical features of apoptosis; flowcytometry analysis showed that after IC50PSPP-Ⅰ treatment, the early apoptosis SGC7901cells rate increased by14.9%and cell cycle disorder, and caused a91.52%-loss ofmembrane potential in SGC7901cells and induced the mitochondrial-mediated apoptosis;Further analysis by real time qPCR results showed that expressions of p53, caspase-3andbax increased respectively2.61,3.09, and2.02times after treated with PSPP-Ⅰfor36h,while the bcl-2-mRNA expressions of declined,0.45times.