Exploration of applying purple passion fruit peel extracts in intelligent shrimp freshness monitoring films

This work aimed to prepare an intelligent visual indicator film for food freshness using natural purple passion fruit peel extracts (PPPEs) as an indicator. The total anthocyanin content in the PPPEs was 3.27 ± 0.07   g/100   g DW, and it showed excellent pH-responsive behavior in the pH range of 6–7. To explore the application of PPPEs in intelligent films, bacterial cellulose nanofibers (BCNFs) were incorporated with chitosan (CS) and chitosan quaternary ammonium salt (CQAS), respectively, as the film matrixes. The effects of different initial pH values of the film solution on the film properties were systematically investigated. The SEM results showed that PPPEs were well dispersed in the film-forming matrixes. The PPPEs/BCNFs/CS pH 2.0 films exhibited good tensile strength (11.97   MPa), with the most sensitive pH color changes and the change in ΔE value of the films was < 5 for the color stability. As the acidity of the film solution increased, the films showed a more sensitive response to the pH change. The PPPEs/BCNFs/CS pH 2.0 films had obvious color changes with the storage of shrimp, which could accurately indicate the freshness, sub-freshness and spoilage status of shrimp. This study demonstrated that the PPPEs exhibited potential for use in the development of intelligent food freshness indicator films.