Assessment of physicochemical characteristics, thermal stability and release profile of ascorbic acid microcapsules obtained by complex coacervation

The aim of this study was to determine the physicochemical characteristics, thermal stability and release profile of ascorbic acid (AA) microcapsules obtained by complex coacervation. Gelatin and gum arabic were used as wall materials in concentrations of 2.5, 5.0 and 7.5 g% (w/v). The coacervate microcapsules were freeze-dried and assessed for physicochemical characteristics, thermal behavior and stability during 60 days of storage. The release profile was evaluated at different pH values (1.1, 2.2, 5.4, 7.4, 9.6 and 12). The encapsulation efficiency ranged from 27.3 to 93.8%. The microcapsules of AA presented good characteristics for application in food matrices, such as average diameter below 12.4 mu m, low solubility and low hygroscopicity. The AA had its thermal stability significantly improved by the encapsulation process, which extends its application in the food industry. The release of AA was slower at pH near neutrality, with release of 97, 96 and 99% of encapsulated AA at 240, 300 and 270 min at pH 5.4, 7.4 and 9.6, respectively. Different mathematical models were successfully fitted to the release kinetics: R-2 > 0.94, absolute deviations < 16% and RMS deviations < 0.09. A mathematical model for a two-step release was proposed, resulting in very high correlations with the experimental data observed: R-2 > 0.99, absolute deviations < 3.5% and RMS deviations around 0.02.