Rational Design of Nano-Silica Composite Indicator Films for Visual Monitoring of Pork Freshness and Shelf-Life Extension

This study presents the development of a novel multifunctional smart packaging film designed to enhance food freshness and possess ammonia-sensing capabilities. The film was fabricated using hydroxypropyl methylcellulose (HPMC) and zinc alginate (ZA), incorporating dragon fruit peel anthocyanins (DE) as pH-sensitive dyes. A hydrophobic layer composed of stearic acid and nano-silica (0.2 g SiO 2 in 1.5 mL solution) was uniformly spin-coated onto the HPMC/ZA/DE film surface and further modified via chemical vapor treatment to improve water resistance. The resulting HPMC/ZA/DE/SiO 2 film demonstrated excellent physical properties, including a high-water contact angle of 116.9°, indicating strong hydrophobicity and effective UV shielding. The film exhibited significant antibacterial activity, achieving 99.99% inhibition rates against Escherichia coli and Staphylococcus aureus . Mechanical tests showed better tensile strength (33.3 MPa) and reduced water vapor permeability (0.33 × 10⁻ 11  g/m·s·Pa) compared to the unmodified control film. In practical application, pork samples wrapped with the smart film were stored at 4 °C for 6 days. A distinct color change from purple to green was observed by day 6, corresponding to elevated pH and TVB-N levels, indicating spoilage. Specifically, on day 9, the packaged pork exhibited a TVB-N value of 49.57 mg/100 g, while the control group reached 51.4 mg/100 g, confirming the film’s spoilage-inhibiting effect. This work offers a promising strategy for developing intelligent active packaging and demonstrates potential for preserving a wide range of perishable foods beyond pork.