High-performance edible alginate straws constructed with zein coatings by phase separation and electrostatic assembly after gradient diffusion

This study developed high-performance, water-resistant edible alginate-based straws by applying a dense zein coating to the surface through controlled phase separation and electrostatic assembly of zein and sodium alginate (SA) following gradient diffusion molding. The zein coating significantly enhanced the anti-swelling properties and surface hydrophobicity of the straws. Specifically, phase separation was introduced by disrupting the alcohol-water solvent system of the zein solution, enabling zein to solidify onto the straw surface. Simultaneously, the negatively charged alginate facilitated electrostatic interactions with the positively charged zein, ensuring stable interlayer bonding. The synergistic regulating of phase separation and electrostatic assembly was systematically investigated to achieve a robust integration with the straw matrix. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) imaging revealed that a continuous and uniform zein coating was formed using a 2 % zein solution at pH 4. Compared to the control, the water resistance of the straw improved significantly, with the water contact angle (1 min) increasing by 45.2 % and the swelling ratio (30 min) decreasing by 53.1 %. Additionally, the straws demonstrated complete degradation within 90 days, outperforming even paper straws. The zein-coated alginate-based straws exhibited superior overall performance, positioning it as a highly promising alternative to plastic straws.