Dual-modulated anthocyanin-based freshness indicators with improved stability using 2,5-dihydroxybenzoic acid and UiO-66-NH2.

Anthocyanins are natural pH-sensitive pigments with potential for intelligent food packaging, but their poor stability under environmental stress limits practical use. Herein, a highly stable intelligent indicator patch was developed by combined incorporation of UiO-66-NH2, a metal-organic framework, and 2,5-dihydroxybenzoic acid. This dual-modulation strategy significantly enhanced anthocyanins stability through hydrogen bonding and van der Waals interactions. The optimized indicator patch maintained color integrity for over 30 days at ambient temperature and more than 6 months at 4 °C in darkness. It exhibited excellent pH responsiveness and high selectivity to spoilage amines (e.g., NH3, dimethylamine, trimethylamine) over common volatile interferents. When applied to Litopenaeus vannamei, the patch's color change correlated strongly with total volatile basic nitrogen (TVB-N) values (r > 0.93), accurately identifying freshness stages. The indicator patch showed high batch-to-batch reproducibility (RSD < 5%) and anti-interference capability. This study provides a feasible approach to commercialize anthocyanin-based freshness indicators for intelligent packaging.