Natural deep eutectic solvent-assisted incorporation of anthocyanins into cellulose acetate nanofibers for halochromic sensors

Intelligent food packaging can help reduce food waste by providing consumers real-time information about product freshness. They can be produced using natural pigments with pH-dependent color changes, which makes them promising candidates for colorimetric sensors. This study reports the development, through solution blow spinning (SBS), of cellulose acetate (CA)-based nanofibers loaded with anthocyanins solubilized in natural deep eutectic solvents (NADES). CA nanofibers were obtained by SBS using CA/PEO (polyethylene oxide) co-solutions, followed by PEO removal. Anthocyanins from grape pomace (GP), sweet potato (SP), and black carrot (BC) were incorporated into pectin solutions solubilized in a choline chloride-glycerol NADES (CC-GLY), which were then used to modify the fibrous membranes by immersion, yielding halochromic sensors. These sensors were characterized regarding their morphological, thermal, and water-related properties. Anthocyanins incorporation decreased CA onset degradation temperatures and increased its melting enthalpy, suggesting improved chain packing. The fibers containing anthocyanins were more hydrophilic and more soluble. Exposure to ammonia vapor produced visible colorimetric responses, with CA/BC achieving the highest ΔE values (24.60 ± 0.50) and a detection limit as low as 1.73 × 10^-6 mol L^-1. Finally, a proof-of-concept assay confirmed CA/BC applicability for monitoring fish (salmon) spoilage via headspace exposure (ΔE = 26.52 ± 0.97 after 144 h at 4 °C and ΔE = 28.49 ± 1.04 after 48 h at 25 °C). The results demonstrate that CA nanofibers doped with anthocyanins are promising natural materials for intelligent packaging applications, enabling rapid and sensitive detection of food spoilage.