A humidity-responsive ethylene sustained-release complex: Encapsulating ethephon with porous starch‑sodium alginate...

The contact application method of ethephon has drawbacks including rapid ethylene release, harmful effects of its products on the human body, and environmental pollution. A controlled-release and low-residue ethephon application technology can effectively address this issue. This study developed a simple and efficient ethylene slow-release technology: ethephon was mixed with porous starch (PS) and sodium alginate (SA) to form a complex via a mixing process, followed by coating a layer of hydroxypropyltrimethyl ammonium chloride chitosan (HACC) shell on its surface. The porous structure of PS provides sufficient loading and storage sites for ethephon. SA endows the composite with humidity responsiveness. HACC inhibits microbial growth by damaging cell membranes, thereby conferring antibacterial properties on the material. Compared with traditional ethylene slow-release technologies, this technology features lower cost, higher loading capacity, easy recyclability and environmental friendliness. Subsequently, the ratio of SA to PS was optimized, with the optimal ratio determined as 1:10. Under this ratio, the ethylene slow-release (ESR) complex achieves a maximum encapsulation efficiency of 52.17% and maintains stable ethylene release for over 120 h. Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD) analyses indicated that ethephon was physically combined with PS without altering the type-A crystal structure of PS. Ethylene release experiments showed that the complex with an ethephon concentration of 350 ppm achieved the optimal release effect, and the ethylene release rate was highly sensitive to humidity. In fruit application experiments, the ESR complex also performed excellently, achieving the dual goals of extending the edible window and preserving the nutritional quality of bananas and kiwifruits, and thus has broad application prospects in fruit ripening and preservation.