Construction of Selaginella-inspired double-walled microcapsules with multistage pH-responsive controlled release and their application in beverages

The high volatility and poor stability of natural essential oils limit their applications, especially in beverages. Inspired by Selaginella's drought-induced shrinkage and rehydration swelling, pH-responsive double-walled microcapsules were built via layer-by-layer self-assembly. The inner network used oxidized γ-cyclodextrin and carboxymethyl chitosan via Schiff base, the outer layer was sodium alginate (SA) and nanocellulose (NC). Lemon essential oil (LEO) was chosen as the core material to verify the effectiveness of the design. The encapsulation efficiency of inner-layer microcapsules achieved 70%. The results of the in vitro pH-responsive release experiment showed that when the ratio of SA to NC in the outer layer was 1:1, the microcapsules exhibited multistage pH-responsive behavior. Under weakly acidic pH conditions, the outer layer structure did not affect the release of the core material, under strongly acidic pH conditions, the release rate was slowed down, thereby achieving effective protection of the core material. In vitro digestion experiments, the bioaccessibility of LEO in Selaginella-inspired double-walled microcapsules was 22.6% higher than that of inner-layer microcapsules. This study provides new research perspectives and a theoretical basis for multistage pH-responsive controlled release microcapsules of natural plant extracts.