Development and characterization of pH-responsive Schiff base-infused pectin/PLA bilayer films for active fruit preservation packaging

This study explores the development of bilayer films composed of pectin and polylactic acid (PLA), incorporating Schiff bases derived from phenylalanine and vanillin at concentrations of 0.25 g/g (P/PLA 0.25) and 0.50 g/g (P/PLA 0.50). For comparative analysis, single-component films of pectin (P 0.25 and P 0.50) and PLA (PLA 0.25 and PLA 0.50) were also prepared. The incorporation of Schiff bases facilitated a pH-responsive release of bioactive compounds in acidic environments, reducing the browning index to 9.35–13.16 after 7 days, compared to 32.26 for LDPE and 46.99 for the control. The bilayer structure exhibited enhanced barrier properties, reducing oxygen permeability to 1.49–1.67 × 10⁻⁴ g/m·s compared to single PLA film (1.92–1.95 × 10⁻⁴ g/m·s). Moisture permeability was significantly decreased to 1.18–1.28 × 10⁻¹ ⁰ g/ms·Pa, while mechanical strength increased by 1.37–1.59 times with higher Schiff base concentrations. Structural and thermal analyses confirmed the successful formation of Schiff bases, which improved the films’ thermal stability and reduced porosity. The bilayer films exhibited notable antioxidant activity, with DPPH radical scavenging ranging from 37.64 % to 67.37 % and ABTS radical scavenging from 77.88 % to 95.36 %. They also demonstrated higher antimicrobial efficacy against E. coli, S. aureus, and A. niger. These combined properties effectively inhibited enzymatic browning and maintained fruit quality during storage. In conclusion, the synergistic interaction between Schiff bases and the pectin/PLA bilayer structure represents a significant advancement in active packaging technology, offering a sustainable solution with potential applications for extending the shelf life of acidic fruits.