Bilayer pH-sensitive colorimetric films with light-blocking ability and electrochemical writing property: Application in monitoring crucian spoilage in smart packaging

Bio-Based Sensors for Smart Food Packaging—Current Applications and Future Trends

“…They are responsible for red, purple and blue color of a variety of plants and fruits and highly reactive to pH changes (their chemical structure changes with the changes in the pH, which result in different colors) [51,80] (Figure 2). A pH-sensitive bilayer hydrogel film was developed using one layer made of gelatin and ZnO nanoparticles incorporated and the second layer made of gellan gum with anthocyanin extracts to monitor fish spoilage [58]. Anthocyanins were extracted from mulberry fruits and their response to pH variations was studied.…”

“…Additionally, the electrochemical writing ability of the films constitutes a green printing technique that allows the display of the information directly on the film, constituting an innovative way to present important information for the consumers. The films developed can act as an intelligent sensor on the detection of fish spoilage [58]. However, no tests were done regarding their antimicrobial and antioxidant activity.…”

“…High temperatures leads to anthocyanins degradation, resulting in browning so lower temperatures are more desirable to maintain their stability [83]. Oxygen and light also contribute to anthocyanins degradation [58,89,90]. To overcome this constraint, bilayer films can be produced where the anthocyanins can be incorporated in the inner-layer, in contact with food, and compounds such as ZnO can be added to an outer layer of the matrix to counteract light induced degradation [58,89,90].…”

“…Oxygen and light also contribute to anthocyanins degradation [58,89,90]. To overcome this constraint, bilayer films can be produced where the anthocyanins can be incorporated in the inner-layer, in contact with food, and compounds such as ZnO can be added to an outer layer of the matrix to counteract light induced degradation [58,89,90]. To develop a feasible film with sensing properties, the use of a proper biopolymer as the polymeric matrix for the incorporation of natural pigments is crucial [91].…”

“…Encapsulation of the pigments can immobilize the compound inside solid particles or liquid vesicles to maintain stability, structure, and also to regulate the release of the pigment [89,99]. The use of nanoparticles, such as ZnO nanoparticles, as UV-light blocking agents is also an effective mechanism to protect and immobilize pigments [58,123]. Nanoclays, such as montmorillonite (MMT), commonly used with reinforcement purposes, also show promising results as pigments stabilizers [123,124].…”