# Ternary Interactions of Starch, Protein, and Polyphenols in Constructing Composite Thermoplastic Starch-Based Edible Packaging: Optimization of Preparation Techniques and Investigation of Film-Formation Mechanisms

## TL;DR

Researchers developed a biodegradable edible packaging material by combining starch, protein, and polyphenols to improve strength and flexibility.

## Contribution

The study introduces a ternary interaction system among starch, whey protein isolate, and gallic acid to enhance film properties.

## Key findings

- Optimized CTPS films achieved a tensile strength of 3.11 MPa and 43.35% elongation at break.
- Ternary interactions via hydrogen bonding and van der Waals forces improved mechanical and antioxidant properties.
- Non-covalent interactions stabilized the starch matrix and WPI structure during film formation.

## Abstract

Biodegradable starch-based films often suffer from insufficient mechanical strength, which limits their practical applications. To enhance film performance, this study optimized the preparation of composite thermoplastic starch (CTPS) films composed of corn starch, sorbitol, whey protein isolate (WPI), and gallic acid (GA). The optimized formulation—0.074 g/mL corn starch, 47.5% sorbitol, 5.6% WPI, and 2.0 mg/mL GA—yielded films with a tensile strength of 3.11 ± 0.31 MPa and an elongation at break of 43.35 ± 0.69%, achieving a desirable balance between flexibility and strength. Mechanistic investigations using in situ Fourier-transform infrared spectroscopy (FTIR), low-field nuclear magnetic resonance (LF-NMR), confocal laser scanning microscopy (CLSM), and molecular docking revealed a ternary interaction system among starch, WPI, and GA. These components primarily interacted through hydrogen bonding and van der Waals forces. Such non-covalent interactions enhanced the short-range molecular ordering of the starch matrix, stabilized the secondary structure of WPI, and facilitated water redistribution during film formation. The resulting interaction network among starch, proteins, and polyphenols significantly improved the mechanical properties and antioxidant capacity of the CTPS films.