Photothermal antibacterial bilayer films from konjac glucomannan/shellac: A Prussian blue-engineered strategy for preservation of fresh-cut Benincasa hispida

PB@MSN-CIN nanoparticles enabled CIN release with NIR-triggered photothermal conversion. • S/P-HK bilayer films combined PB@MSN-CIN-loaded P-HK inner layer with a hydrophobic SHL-QCT outer layer. • Regulating the SHL-QCT layer thickness improved moisture barrier, UV shielding, and photothermal retention of the bilayer films. • Under NIR treatment, the optimized S/P-HK film suppressed microbial growth, browning, and water loss of fresh-cut Benincasa hispida . Fresh-cut vegetables are highly susceptible to microbial growth, enzymatic browning, and moisture loss, creating a need for environmentally sustainable active packaging with effective barrier and antimicrobial functions. In this study, a multifunctional bio-based bilayer film (S/P-HK) was developed using the thickness of the hydrophobic outer layer as a key design variable. The inner active layer (P-HK) comprised a konjac glucomannan/hydroxyethyl cellulose matrix containing cinnamaldehyde (CIN)-loaded mesoporous silica nanoparticles coated with Prussian blue (PB@MSN-CIN), whereas the outer layer was composed of quercetin-containing shellac (SHL-QCT). SEM revealed a compact bilayer structure, while FT-IR, XRD, and TGA indicated intermolecular interactions and good thermal stability. Increasing the thickness of SHL-QCT layer enhanced moisture-barrier performance and heat retention under near-infrared (NIR) irradiation. Among which, the S20/P-HK film exhibited nearly complete UV shielding, strong antioxidant activity (DPPH and ABTS radical scavenging rates >80%), excellent antibacterial activity (antibacterial rates >99.99% against Escherichia coli and Staphylococcus aureus ), and controlled release of CIN. During preservation of fresh-cut Benincasa hispida , the S20/P-HK film with NIR irradiation significantly inhibited microbial growth, suppressed the browning index to 0.90 ΔOD₄₂₀·mL/g, and restricted weight loss to 0.26% over 10 days. These findings demonstrate a promising thickness-regulated bilayer design that integrates moisture-barrier protection, NIR-responsive CIN release, and photothermal antibacterial activity for active packaging. Future studies should validate the applicability of S/P-HK films to other perishable foods and evaluate their antifungal efficacy. Download: Download high-res image (168KB) Download: Download full-size image