pH-indicating properties and storage stability of a smart edible film based on nopal-mucilage/gellan gum and red cabbage anthocyanins

Nopal mucilage is a complex polysaccharide with great potential in the preparation of the films to food packaging. In this work, was develop a smart edible film with pH-indicating capabilities based on nopal mucilage, gellan gum, and red cabbage anthocyanins (70:20 w/w, and 10% respectively). Physical properties, appearance, and colorimetric functionality were characterized to pH range 2.5-5.9. Color stability, measured by CIELAB, was tested with different storage conditions and time and interpreted by differential tristimulus colorimetry. Results showed films whit uniform appearance, flexibility, easy-handling, and excellent color response within the pH range studied. The evolution of color difference (ΔE*ab) confirmed that the colorimetric functionality of films was stable at short storage periods (8 days) under natural conditions of sunlight and oxygen exposure, while a more extended storage period was affected. Results showed that the film is an excellent barrier and presents color changes triggered by pH changes.