Electrospun pectin/polyvinyl alcohol smart nanofiber indicators incorporating red radish peel extract for real-time monitoring of rainbow trout freshness

A colorimetric indicator based on electrospun orange-peel (OP) and banana-peel (BP) pectin/PVA nanofibers incorporating red radish peel extract (RRPE) was developed to monitor rainbow trout freshness under refrigeration. In agar well diffusion assays, RRPE exhibited 25.2–27.8 mm inhibition zones against four common foodborne pathogens. FTIR confirmed RRPE incorporation, XRD showed a predominantly amorphous structure, and TGA showed pectin-source-dependent effects of RRPE on thermal stability. RRPE enhanced moisture barrier properties, hydrophobicity, flexibility, and antioxidant activity (74–75%). The two smart indicators showed different color changes across a broad pH range and achieved RGB sensitivity values of 64.51% (OP/PVA/RRPE) and 63.96% (BP/PVA/RRPE) after 24 min of ammonia exposure. Visual color changes agreed with increases in pH (6.27–7.47), TVB-N (10.73–26.13 mg N/100 g) and TBA (0.15–1.06 mg MDA/kg). The two pectin-based indicators exhibited statistically equivalent sensing performance (Fisher’s r-to-z, p > 0.05), providing flexibility in feedstock selection based on economic or yield considerations. Although OP/PVA/RRPE had finer fiber morphology and better moisture-barrier performance, both systems performed with comparable efficiency in real-time monitoring of fish freshness. The developed bio-based indicator provides a natural and promising platform for real-time monitoring of rainbow trout spoilage.