Effect Of Steam Explosion On Physical And Chemical Properties And Antibacterial Properties Of Active Components Of Purple Sweet Potato

Purple sweet potato(Ipomoea batatas(L.)Lam)has relatively high levels of anthocyanins and polysaccharides,both have diverse biological activities.In this thesis,purple sweet potato was pretreated by steam explosion.The extraction and purification of polysaccharides and anthocyanins from purple sweet potato was studied,while their structure and physicochemical properties were investigated as well.The main contents of this thesis are as follows:1.Purple sweet potato was pretreated by steam explosion and further utilized for polysaccharide extraction.The scanning electron micrographs show that the untreated purple potato has a loose structure and contains a large number of starch granules.After steam explosion,the starch granules were gradually disappeared and tend to form a smooth surface of purple sweet potato with a tight-binding stucture.Single factor experimental design and Box-Behnken design were applied to evaluate the steam explosion process.The optimal explosion condition was determined by the response surface analysis and listed as follows: steam explosion pressure 1.65 MPa,residence time 48.26 s,water content 10.87%.Under this condition,the yield of purple sweet potato polysaccharide was 11.45%.2.Polysaccharide extracts were purified using DEAE-52 cellulose column.UV spectra show that both SEP-PSPP II and SEP-PSPP III had a weak absorption peak around 280 nm.IR spectra show that all of the polysaccharides are ?-pyranose configuration.Characteristic absorptions of carboxyl group does not exist in the spectra of both PSPP I and SEP-PSPP I,but were detected in the spectra of PSPP II,PSPP III,SEP-PSPP II and SEP-PSPP III,which are acidic polysaccharides base on the the uronic acid analysis.The polysaccharide composition was analyzed by HPLC after PMP derivatization.The results showed that PSPP I and SEP-PSPP I was mainly composed of rhamnose,glucose,xylose and galactose while PSPP II,PSPP III,SEPPSPP II and SEP-PSPP III were in addition of glucuronic acid.Steam explosion pretreatment would increase the content of glucose,xylose and glucuronic acid in purple sweet potato polysaccharides.3.The results of in vitro antioxidant activity assay showed that the free radical scavenging ability of purple sweet potato polysaccharide was increased with an increment of its concentration.The removal rate of ·OH radicals of steam-pretreated polysaccharides was higher than that of untreated ones,reached with a maximum of 62.88%.The DPPH scavenging activity of steam-pretreated polysaccharides reached 70.8%,which was about 1.3 times that of untreated ones.The reduction power was significantly improved after steam explosion pretreatment.The results of antibacterial properties showed that purple sweet potato polysaccharide had inhibitory effect on Staphylococcus aureus,Escherichia coli and Bacillus subtilis,but no inhibion on Salmonella.The results of the Minimum Inhibitory ConcentrationTest(MIC)indicated that steam explosion pretreatment could enhance the sensitivity of purple sweet potato polysaccharide to Bacillus subtilis and decrease the minimum inhibitory concentration from 10 mg/mL to 5 mg/mL.4.Anthocyanins were purified from ethanol extracts of purple sweet potato with macroporous resin.HPLC analysis showed that the peaks of both ethanol extracts are anthocyanins,but the relative content of their components were different.The results of in vitro antioxidant activity assay showed that the ability to remove DPPH free radicals and hydroxyl radicals was enhanced by steam explosion but no significant improvement of reducing power.The results of antibacterial properties showed that purple sweet potato anthocyanin had strong inhibitory effects on Staphylococcus aureus,Escherichia coli,Bacillus subtilis and Salmonella.The minimum inhibitory concentration(MIC)was 0.125 mg/mL,0.25 mg/mL,0.25 mg/mL and 0.0625 mg/ mL,respectively.