A Green Method for Nanoencapsulation of Thymol in Chitosan–Gelatin with Antioxidant Capacity

Abstract

Nanostructures are usually formed by solvent dissolution, but this paper proposes a green-chemistry method for thymol nano-encapsulation based on a chitosan–gelatin bio-copolymer matrix formation that enhances the physical stability to obtain a thymol-modified release system, with antioxidant capacity. Various ratios of chitosan–gelatin, gelatin types A and B, and crosslinkers were evaluated at a constant thymol concentration of 0.5 mg/ml. Gallic acid was chosen as the crosslinker. All batches were ultrasonicated to reduce particle size. The best conditions were obtained using a chitosan–gelatin ratio of 1:4 with type A gelatin, as those nanoparticles had higher physical stability, together with a smaller particle size (316.5 ± 2 nm) and higher thymol encapsulation efficiency (88 ± 3%). Antioxidant capacity was evaluated by DPPH, ABTS (radical inhibition 87.06 ± 4.38%, and 88.5 ± 4.42%, respectively), and a FRAP assay (1084.68 ± 54.32 µM Trolox equivalents). Release profiles were evaluated at two pH values (5.5, 7.0) and environmental temperatures (4, 25 °C). Diffusion was non-Fickian in all treatments. Gelatin type A systems exhibited a major physical stability, influencing the reduction of released thymol significantly. The research findings suggest that this submicronic dispersion can be used as a modified release system with high antioxidant activity and potentially serve as a preservative system during food storage.