Alfianita Nuril Hidayaty, Saidun Fiddaroini, Ahmad Luthfi Fahmi, Dea Luthfianti Maharani, Qonitah Fardiyah, Arie Srihardyastutie, Akhmad Sabarudin
Ensuring fish freshness is critical for food safety, yet conventional assessment methods are destructive and unsuitable for real-time monitoring. This study develops a pH-responsive colorimetric film based on a chitosan–polyvinyl alcohol (Cs/PVA) matrix incorporated with red amaranth (Amaranthus tricolor L.) leaves extract (RAE), a highly betacyanin-rich natural pigment source. LC-HRMS analysis identified betacyanin (C₃₀H₃₄N₂O₁₉) as the dominant metabolite with the highest ion area (1.15 ×10 ¹⁰), alongside phenolics, carotenoids, and alkaloids that may enhance stability and responsiveness. UV–Vis characterization revealed a strong absorption peak at 535 nm and a total betacyanin content of 261 mg/L, with marked spectral shifts and color degradation above pH 9. Five film formulations were produced by varying extract volume of 1–5 mL (RAE1–RAE5), corresponding to 0.261–1.305 mg/L betacyanin. Film thickness increased with pigment loading (0.085 ± 0.01–0.138 ± 0.02 mm). FESEM revealed improved uniformity in RAE4, while FTIR confirmed strong hydrogen-bonding interactions between betacyanin and the Cs/PVA matrix. The films displayed distinct color transitions across pH 5–9, with ΔE values exceeding 50 for RAE4 and RAE5. Ammonia-vapor assays demonstrated high sensitivity, achieving > 50 % response within 180 min at 1 % NH₃. Application to tilapia fillets stored under refrigerated (6 ± 1 °C, 11 days) and ambient (23 ± 1 °C, 24 h) conditions showed strong correlation between film responses, pH elevation, and sensory quality decline. These findings establish red amaranth as a potent natural pigment and identify Cs/PVA-RAE4 and Cs/PVA-RAE5 films as sensitive, stable, and scalable freshness indicators suitable for real-time food monitoring. © 2026 Elsevier B.V.
Department of Chemistry, Faculty of Science, Brawijaya University, Malang, Indonesia; Research Center for Advanced System and Material Technology, Brawijaya University, Malang, Indonesia
