Humidity-responsive composite film for strawberry freshness control

In this study, a cellulose nanocrystal (CNC)-based double-layer smart packaging film with both humidity-responsive and antimicrobial functionalities was developed for strawberry preservation and real-time freshness monitoring. CNC was extracted via sulfuric acid hydrolysis and modified with glycerol (Gly) to modulate its humidity-responsive properties, enabling reversible color transitions from blue to red within 30–98 % relative humidity (RH). Zein/gelatin (Gel) nanofiber layers loaded with 3 % Thymol (Thy) in a mass ratio of 1:1 was fabricated using electrospinning technology, achieving an encapsulation efficiency >85 % and inhibition zones of 21.3 ± 0.5 mm (Botrytis cinerea) and 20.8 ± 0.4 mm (Aspergillus niger). The composite film exhibited a significantly reduced water vapor transmission rate (3.81 × 10⁻¹¹ g Pa⁻¹·s⁻¹·m⁻¹), indicating excellent moisture barrier properties. Strawberry preservation experiments demonstrated that the composite film effectively delayed hardness reduction (61.5 % of initial firmness retained), reduced weight loss to 8.5 %, and suppressed mold growth (<10³ CFU/g). Through smartphone RGB analysis, the film color gradient (blue-orange-red) exhibited strong correlations with freshness indicators (hardness; mold colony count (CFU/g)), enabling non-destructive real-time monitoring. This study introduces an eco-friendly, cost-effective packaging solution that offers real-time freshness monitoring and prolonged strawberry preservation, paving the way for industrial applications in smart food packaging.