Deep Eutectic Solvent–Sodium Carboxymethyl Cellulose Synergistic Enhancement of High-Performance Starch-Based Edible Carrier: Studies from Molecular Interactions to pH Response Performance

Although starch-based edible capsules are ideal carriers, their poor mechanical properties limit their practical use. To improve the mechanical properties of the material, this study aimed to synergistically reconstruct the hydrogen-bond network of the hydroxypropyl starch (St) matrix using a deep eutectic solvent (DES) and sodium carboxymethyl cellulose (CMC). The results showed that the mechanical properties of the betaine–lactic acid–glycerol (B-LA-G)/CMC-St composite film were improved compared with St, with tensile strength and elongation at break increased by 15.97 and 29.96%, respectively. Meanwhile, the B-LA-G/CMC-St edible carrier showed good short-term storage adaptability, with its drying loss (13.43 ± 0.03%), disintegration time, and friability (4 pieces), conforming to the requirements of the Chinese Pharmacopoeia. A significant color difference (Δ E > 2) was observed for the capsules across a range of pH levels. Electrostatic potential (ESP) and reduced density gradient (RDG) revealed the strength (−477.85 kcal/mol) and type of interaction between the B-LA-G/CMC-St components.