Halochromic smart film: a gelatin-based pH-sensitive film embedded with anthocyanin from roselle (Hibiscus sabdariffa) extracts for potential food spoilage indicator application

This study developed and characterized a pH-sensitive gelatin-based film incorporated with anthocyanin from roselle extracts (Hibiscus sabdariffa) at varying concentrations (0%–15%). The addition of anthocyanins significantly influenced the film's properties, reducing tensile strength from 1.5 to 1.1 MPa while increasing elongation at break from 312% to 416%. Water vapor permeability also increased with anthocyanin concentration, ranging from 1.02 to 1.47 × 10−⁸ g·m−¹·s−¹·Pa−¹. The film displayed a distinct color change from red to yellow-green across pH 3–10 and when exposed to ammonia gas, highlighting its potential for real-time detection of volatile basic compounds. Fourier transform infrared analysis revealed molecular interactions between gelatin and anthocyanins, with increasing roselle extract concentrations as it showed enhanced amide A, I, II, and III functional groups. Scanning electron micrographs revealed increased surface roughness and microstructural changes with anthocyanin addition. These findings demonstrate the potential of 15% roselle anthocyanin–gelatin films as eco-friendly, pH-sensitive smart packaging materials for food applications.