Advanced smart nonwovens for food quality monitoring: ultrathin and highly porous polymer fibers via electrically-assisted supersonic solution blow-spinning.

Enhancing porosity and reducing fiber diameter significantly improves the sensitivity of nanofibers as colorimetric indicators, making them ideal for food quality monitoring. In this study, ultrathin and highly porous PCL-based nonwoven mats were developed as colorimetric indicators for detecting food spoilage, using a combination of non-solvent-induced phase separation and electrically-assisted supersonic solution blow spinning (EASBS). The nonwovens incorporated natural (curcumin and alizarin) and synthetic (bromophenol blue) pH indicators. For comparison, non-porous nanofibers were also produced via EASBS, and highly porous fibers via conventional solution blow spinning (SBS). Although the incorporation of indicators increased the fiber diameter, EASBS still resulted in finer fibers than SBS. The EASBS porous mats also exhibited the highest specific surface area, compared to SBS and EASBS non-porous specimens, contributing to their enhanced responsiveness to analytes. The EASBS nonwoven polycaprolactone/bromophenol blue specimens revealed the best performance, with the lowest limit of detection and limit of quantification for volatile amines. During storage, the values of the overall color change (ΔE) for polycaprolactone/bromophenol blue mats revealed pronounced visually perceptible color changes with ΔE increasing from 0.00 at baseline to 7.76 after 24 h and 19.21 after 72 h. Initially yellow, the mats turned green within 24 h, and the degree of greenness intensified over 72 h, consistent with spoilage parameters observed in the fish fillets (pH 8.01 and total volatile basic nitrogen of 24.73 mg/100 g). Furthermore, the nonwovens responded visibly to Escherichia coli K-12 contact within 24 h and maintained color stability over 30 days, confirming their potential as intelligent, highly-responsive indicators for food freshness monitoring.