Abstract:To fabricate freshness-indicating films for Metapenaeus ensis, gelatin/polyvinyl alcohol composites were used to form films, and blueberry anthocyanin and gallic acid were used as indicator and co-pigment, respectively. Ultraviolet-visible spectra, infrared spectra, microscopic observation, and mechanical properties revealed that addition of gallic acid enriched the colors exhibited by anthocyanin under different pH conditions. No new peak appeared with the addition of anthocyanin and gallic acid, indicating good compatibility of these compounds with the film-forming matrix. The elongation at break point of the composite films was between 1 000% and 1 200%, and the films exhibited moderate tensile strength and thickness. Compared with that of the anthocyanin film, the ΔE value of the composite film was significantly increased (P<0.05). The cross-section of the composite films was smoother with a small amount of gallic acid (anthocyanin: gallic acid m/m = 1:0.3 and 1:0.5). When used to indicate freshness of M. ensis, spoilage was detected between 24 and 48 h, with total volatile basic nitrogen content of M. ensis gradually increasing, and ΔE of the indicator film showing a significant change (P<0.05). The color of the composite films containing gallic acid changed from gray to yellow, which was easier to recognize with the naked eye. Therefore, the composite film containing anthocyanin and gallic acid can realize improved indication of M. ensis spoilage. This study provides a reference for research into freshness indicator films for different aquatic products.
