Amphiphilic carboxymethyl chitosan micelle-based indicators for enhanced stability and real-time, non-destructive monitoring of fresh-cut kiwifruit spoilage

Monitoring spoilage of fresh-cut fruits is vital for reducing postharvest losses and facilitating intelligent, consumer-responsive food packaging. In this study, we report the first development of a CO 2 -responsive indicator system based on amphiphilic nanomicelles derived from carboxymethyl chitosan (CMCS), a natural, biodegradable polysaccharide. Oleic acid was grafted onto CMCS to produce CMCS-g-OA micelles capable of encapsulating hydrophobic pH-sensitive dyes (bromothymol blue and methyl red). Structural characterization (FT-IR, 1 H NMR) confirmed successful amidation, resulting in stable core–shell micelles (179.0–311.8 nm, −24.7 mV, PDI < 0.5). These micelles exhibited distinct, reversible color transitions (light green to orange) in response to CO 2 generated during spoilage. For practical applications, they were embedded into a gelatin/polyvinyl alcohol (PVA) matrix to fabricate flexible biopolymer-based indicator films with enhanced mechanical properties and color stability (ΔE < 5). When applied to monitor fresh-cut kiwifruit, the system enabled non-destructive, real-time visual differentiation of spoilage stages, achieving 91.22 % classification accuracy via principal component analysis (PCA). This work presents a novel micelle-based sensing technology that integrates bio-derived polymers with intelligent gas responsiveness. To the best of our knowledge, this is the first report of CMCS-based amphiphilic micelles used for freshness indication, offering a sustainable and scalable strategy for real-time monitoring in intelligent food packaging applications.