Extraction, Separation And Antimicrobial Activities Of Bamboo Leaves Flavonoids

Flavonoids in bamboo leaves is a natural surfactant and has many bioactivities such asantibacterial, anti-free radicals, antioxidant, insecticidal, anti-tumor, anti-aging, blood fatand blood cholesterol whitening activity. In present work, the solvent refluxing process andmacroporous resin adsorption were adopted to extract and purify bamboo flavonoids, andseparated products were used for preservation of Soya-bean milk. The research resultsprovide theoretical basis for preparation of the natural food preservative and fresh-keepingof soy products.Flavonoids from bamboo leaves were extracted by solvent refluxing process, andorthogonal test was employed to optimize the extracting parameters. The influences ofvarious factors on extraction rate of total flavonoids were investigated systematically,including extraction processes, raw material granularity, type and concentration of solvent,ratio of the solid to solvent, extraction temperature and time. The experimental resultsshowed that extraction rate of flavonoids with solvent refluxing extraction was higher thanthose with ultrasonic wave extraction, percolation and cold soak extraction, but rawmaterial granularity had a slight effect on the extraction rate of flavonoids. The extractionrate of flavonoids was98.09%, and the content of flavonoids in extraction product reached14.87%with60%of volume concentration ethanol aqueous solution as solvent and withthe ratio of bamboo leaves to solvent at1:16(g: ml) under70℃for2.5h,1.5h,1.0h,respectively.Static sorption experiments had been carried out to determine the adsorptionequilibrium and kinetics of bamboo flavonoids onto macroporous resins at differenttemperatures. It was found that AB-8macroporous resin had high selectivity and gooddesorption property, and its saturated adsorption capacity reached20.64mg/g at303K.Freundlich equation was found to be the best one for the description of the adsorptionequilibrium of bamboo flavonoids on AB-8resin, and the negative value of ΔG and thepositive value of S showed that the adsorption was a spontaneous process of increasedentropy, and the increase of temperature would benefit the adsorption process. Theadsorption heat H was13.45kJ/mol within the range of hydrogen bond energy, whichsuggested that the adsorption of bamboo flavonoids on AB-8resin was a type of physicaladsorption with hydrogen bond. The kinetics results revealed the adsorption followed apseudo-second-order reaction, and the film diffusion played an important role in the controlstep of the adsorption rate. The results of dynamic adsorption-desorption experiments revealed that the saturationadsorption capacity of bamboo flavonoids on AB-8resin achieved19.56mg/g under theoptimum condition, with initial flavonoids concentration of1.0mg/ml, pH6.0, the ratio ofcolumn height to diameter3.3:1and adsorption flow rate1BV/h. The yield and the contentof the product was22.11%and34.35%, respectively, with aqueous ethanol solution of10%,20%,30%and40%(V/V) gradient elution.71.42%of flavones absorbed on macroporousresin can be eluted by3.27BV ethanol aqueous solution of30%(V/V) at1BV/h. Thecontent of flavones can reach above35%with flavones yield of24.88%under the optimumconditions of purification. Four type of flavonoids were detected by HPLC-MS in separatedproducts following macroporous resin adsorption, which were rutin,quercetin-3-O-beta-D-glu(1-2)-alpha-L-rhamnopyranoside,isorhamnetin-3-O-beta-D-rutinoside, orient-in glycosides or isoorientin, respectively.Effects of bamboo flavonoids (BLF) on the antibacterial efficacy to several commonbacteria from food were investigated by the plate culture count. The minimum inhibitoryconcentration (MIC) of BLF against Escherichia coli, Staphylococcus aureus, Yeast,β-alkaliphilic bacillus and the preservation effect of Soya-bean milk had been determined.The experimental results showed that BLF exhibited an antimicrobial activity againstEscherichia coli, Staphylococcus aureus and β-alkaliphilic bacillus with MIC of BLF at0.029mg/ml,0.0180mg/ml,0.0700mg/ml, respectively, while no significant antibacterialactivity against yeast was observed. Result of antimicrobial rate showed that thefresh-keeping effect of BLF with0.01%(wt%) dosage on Soya-bean milk was obvious at4℃, and the optimum concentration of BLF was0.015%(wt%) at30℃. Sensoryevaluation displayed that0.01%-0.015%(wt%) of BLF almost had no influence on thecolor and flavor of Soya-bean milk, and BLF could prolong its preservable time from8h to14h. There was a synergistic effect of Vanillin and BLF against spoilage microorganismsof Soya-bean milk, and the shelf life of Soya-bean milk could be prolonged from8h to16h when0.015%(wt%) of the BLF and Vanillin mixture (the mass ratio of BLF to Vanillin4:1) was added at30℃.