The Research On Extraction Technology Of Polysaccharide And Flavonoids From Sweet Potato Leaves And Its Bacteriostasis

To research and develop sweet potato leaves further, the best technological conditions to extract polysaccharide and flavonoids from sweet potato leaves were determined through single-factor and orthogonal intersection experiments. The yield of polysaccharide was 4.15% at the best technological conditions in hot water as following--the temperature of extraction was 100℃, the time of extraction was two hours, the ratio of sample to water was 1:30(m/V)with 95% ethanol. The yield of flavonoids was 8.48% at the best technological conditions as following-- the concentration of ethanol was 95%, the time of ultrasonic was 45 minutes, the ratio of sample to water was 1:40.Then the antimicrobial activity of polysaccharide and flavonoids to several kinds of microorganism and the stabilities of polysaccharide and flavonoids to pH value, metal ion, temperature and UV radiation were also researched. The result showed that polysaccharide could effectively inhibit the growth of a series of microorganism especially E.coli.. But it had indistinctive inhibition on Saccharomyces cerevisiae and mucor and no effect on rhizopus. The MIC of E.coli., Staphylococcus aureus and Bacillus subtilis was 1.25 mg/mL, 2.5 mg/mL and 5 mg/mL each. It could facilitate the antimicrobial activity of polysaccharide at neuter and acidic pH of 5-7. UV radiation and metal ion(Na⁺,K⁺,Ca²⁺,Fe²⁺,Fe³⁺) had hardly effect on its stability. And high temperature could eliminate distinctly the antimicrobial activity of polysaccharide.Flavonoids could effectively inhibit the growth of a series microorganism especially Staphylococcus aureus. But it had indistinctive inhibition on Rhizopus and mucor and no effect on Saccharomyces cerevisiae. The MIC of Staphylococcus aureus, E.coli., Staphylococcus aureus and Bacillus subtilis was 1.25 mg/mL, 5 mg/mL and 5 mg/mL each. It could facilitate the antimicrobial activity of flavonoids at neuter pH of 7. UV radiation and metal ion(Na⁺,K⁺,Ca²⁺,Fe²⁺,Fe³⁺) had hardly effect on its stability. And high temperature had indistinctive effect on the antimicrobial activity of flavonoids. Through the experiments under different systems such as the DPPH system, Feton system and linolic acid peroxide system, the antioxidant ability of extract from sweet potato leaves was researched. The result showed polysaccharide and flavonoids from sweet potato leaves both had a strong ability on scavenging free radical and a weak ability on anti-lipid peroxidation.The antisepsis experiments with some representative food were also researched. The result showed that polysaccharide and flavonoids from sweet potato leaves had a good preservative effect on food.