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 (<10 3 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.