Formulation, Stability, and pH-Responsive Release of Freeze-Dried Microcapsules Containing Averrhoa bilimbi L. Leaf Extract Anna Safitri[1, 2], Sutrisno Sutrisno[1], Kana Mardhiyyah[3,4], Kholaf Athallah Vyanto[1], Wasilia Wulandari[1]
1. Department of Chemistry, Faculty of Mathematics and Natural Sciences, Brawijaya University, Jl. Veteran, Malang, 65145, Indonesia
2. Research Centre of SMONAGENES (Smart Molecules of Natural Genetic Resources), Brawijaya University, Jl. Veteran, Malang, 65145, Indonesia
3. Department of Biochemistry & Biomolecular, Faculty of Medicine, Universitas Brawijaya, 65145 Malang, East Java, Indonesia
4. Master Program in Biomedical Science, Faculty of Medicine, Universitas Brawijaya, 65145 Malang, East Java, Indonesia
Abstract
The instability and limited bioavailability of flavonoid-rich plant extracts remain major challenges for their application in functional food and pharmaceutical systems. This study aimed to optimize the microencapsulation of Averrhoa bilimbi L. ethanolic leaf extract using sodium alginate through Response Surface Methodology based on a Central Composite Design. Alginate concentration (0.5 to 2.5 percent w/v) and stirring time (5 to 70 min) were evaluated as independent variables affecting encapsulation efficiency. The optimized condition (1.5 percent alginate and 37.5 min stirring) achieved a maximum encapsulation efficiency of 81.12 percent, with a highly significant quadratic model (R2 = 0.9810). Scanning Electron Microscopy analysis revealed irregular but structurally intact microcapsules with particle sizes ranging from 7.87 to 11.68 um, characteristic of freeze-dried systems. Fourier Transform Infrared spectra confirmed successful ionic cross-linking between alginate and Ca2+, as well as the presence of flavonoid functional groups within the matrix. Antioxidant evaluation showed strong radical scavenging activity, while pH dependent release studies demonstrated limited release under acidic conditions (26.30 percent at pH 2.2) and significantly enhanced release at intestinal pH (67.79 percent at pH 7.4). Kinetic modeling indicated a transition from diffusion controlled release under gastric conditions to swelling assisted transport at intestinal pH. Stability studies over four weeks revealed markedly improved antioxidant retention in microcapsules compared to non-encapsulated extract, particularly under cold storage. Overall, this study demonstrates that RSM optimized alginate microencapsulation effectively enhances the stability and controlled intestinal release of A. bilimbi L. flavonoids, highlighting its potential for nutraceutical and functional food applications.
