Preparation,Structure And Property Of Ascorbic Acid-loaded Alginate/chitosan Microcapsules

In this study,based on sodium alginate/chitosan as the controlled-release carrier,ascorbic acid-loaded sodium alginate/chitosan microcapsules were successfully prepared via ionotropic/external gelation technique.The microcapsules were analysed by laser particle size analyzer,scanning election microscopy(SEM),fourier transform infrared spectroscopy(FT-IR),X-Ray diffraction(XRD)and Differential scanning calorimetry(DSC)to characterize the structure of the microcapsules and their swelling and antibacterial properties.The improvement of ascorbic acid's resistance to light,heat and oxidant through the encapsulation by sodium alginate/chitosan microcapsules were analysed and its ability of scavenging free radicals were also studied.The controlled-release of ascorbic acid encapsulated in microcapsules was analysed in different buffer solution,and the release kinetics was also studied.The results were shown in the below:1.The results of FTIR,XRD and DSC showed that ascorbic acid,alginate and chitosan were not a simply physical mixture.There was electrostatic interaction between alginate and chitosan to form polyelectrolyte complex.Ascorbic acid did not change the amorphous phase property of sodium alginate/chitosan microcapsules,and a successfully molecular level dispersion of ascorbic acid happened in the polymer blend matrix.2.Swelling studies showed that ascorbic acid-loaded sodium alginate/chitosan microcapsules had obvious swelling performance.And with different pH,swelling index(SI)varied substantially,the swelling behavior showed strong pH sensitivity.The SI value of microcapsules in pH 2 was within the range between 92-135%,in water was 307-335%and in pH 7 was 705-751%.Antibacterial performance showed that the combination of ascorbic acid and chitosan made the AA-loaded microcapsules not only have the bioactivity of ascorbic acid but also gain the antibacterial ability of chitosan.3.Encapsulation by sodium alginate/chitosan microcapsules provided significant protection for ascorbic acid against light-,heat-exposure degradation and oxidation by oxidant.After 7 days of UV exposure and 40,60,80 ? heating,the residual rates of ascorbic acid in ascorbic acid-loaded microcapsules were 90.31%,92.68%,91.17%and 82.32%respectively,but the pure ascorbic acid were 19.95%,26.07%,21.87%,15.72%.These indicated the well protection of microcapsules for ascorbic acid against light-,heat-and oxidant.Soaked in he same concentration of lmol/L hydrogen peroxide solution,pure ascorbic acid disappeared entirely in less than 1 hour,however,only 4.2%of ascorbic acid in sodium alginate/chitosan microcapsules suffered oxidation decomposition under the same condition,and even had 11.8%residual even after a week.4.Ascorbic acid-loaded sodium alginate/chitosan microcapsules had strong ability for scavenging free radicals,and still maintained the ability even after UV and heating exposure.After the seven days of UV exposure,the removing HO.ability of ascorbic acid-loaded microcapsules remained high and presented EC50=4.20 mmol/L,but the pure ascorbic acid presented EC50= 26.58 mmol/L.The former was 6.33 times of the later under the same condition.After the seven days of 80 ? heating,the removing HO· ability of ascorbic acid-loaded microcapsules remained high and presented EC50= 4.61 mmol/L,but the pure ascorbic acid presented EC50= 33.74 mmol/L.The former was 7.32 times of the later under the same condition.5.Ascorbic acid-loaded sodium alginate/chitosan microcapsules allowed the controlled release of ascorbic acid in a long time,which showed good release property.The released kinetics of microcapsules contained contributions both from Fickian diffusion and polymeric relaxation of the hydrophilic matrix,and polymeric relaxation is the mechanism prevailing in release profile of ascorbic acid from sodium alginate/chitosan microcapsules.