Study On Extraction,Purification And Invitro Antitumor Activity Of Exopolysaccharides From Streptococcus Thermophilus

The optimal fermentation conditions to the highest yield of extracellular polysaccharide(exopolysaccharide,EPS) produced by Streptococcus thermophilus isolated from Tibetan Saussurea were studied.And EPS was isolated and purified.The invitro antitumor activity of EPS was studied. For functional studies of Lacticacid bacterium EPS has provides a theoretical basis.The results indicate that the appropriate substrat for exopolysaccharides production is improved IRIE.The optimal fermented conditions were determined by L9(33)orthogonal experiments.The optimal fermentation conditions with Streotococcus thermophillus were42℃for48h,inoculation size3%(v/v).The results show the yield of EPS with controlling pH6.0was increased by11.2%compared with no controlling.After the fermentation broth was washed three times by Sevag,the yield of EPS was46.73%and deviation rate of protein was59.87%.The supermatant after protein activated was concentrated and filtrated by ultrafiltration(MWCO5kDa).Its membrane flux was15.3L/m2·h and the yield of EPS in filtrate.The retentate was concentrated for4times.Then the EPS were precipitated from the supernatant with three volumes of ethanol and the yield of EPS was367.8mg/L.The EPS was further purified by column chromatography on DEAE-Sepharose52and Sepharose CL-6B.EPS1,EPS2and EPS3were achieved. EPS1a and EPS1b were obtained by EPS1.EPS3were thought to be neutral polysaccharides.The purity quotient of EPS1a,EPS1b,EPS2and EPS3were97.0%,91.59%,91.58%and96.1%,and the molecular weight were6.42×102Da,3.48×103Da,3.35×104Da and5.63×103Da in the determination by HPLC.The result of invitro experiment showed that every constituents of EPS can inhibit the proliferation of Hela. The concentration was higher,and inhibition ratio was better.The invitro antitumor activity was the highest when the concentration of EPS was500μg/mL.And inhibition ratio was25.3%.