In vitro degradation of serum albumin microcapsules: effect of process variables

Microcapsules were prepared by cross-linking of human serum albumin (HSA) with terephthaloyl chloride (TC). Reaction pH was increased from 5.9 to 11, using 2.5% TC and 30 min reaction time. Then, in two series of assays conducted at pH 9.8, TC concentrations were varied from 0.5 to 5% (with 30 min reaction time), and reaction time was increased from 2 to 60 min (with 2.5% TC). Finally, two series of experiments were performed at pH 7.4 and 8, respectively, combining 2.5 and 5% TC with 30 and 60 min reaction time. Microcapsule degradation in pepsin (pH 1.2), and in trypsin (pH 7.5) was studied by microscopic examination. In the pH series, microcapsules prepared at pH ≤8 were degraded by pepsin within 50–70 min, while those obtained at pH ≥9 were resistant. Solubilisation time in trypsin was 3–10 min for pH ≤8, and 20–40 min for pH ≥9. At pH 9.8, resistance to pepsin was observed whatever the reaction time and the TC concentration, while solubilisation time in trypsin was 15–30 min. At pH 7.4 or 8, microcapsules were degraded in pepsin (50–70 min) and in trypsin (8–15 min). The results demonstrate the determining influence of reaction pH on microcapsule degradation. Besides, a correlation was found between microcapsule sensitivity to pepsin and high–NH₂ contents found in previous studies.