Intelligent pH-responsive films based on natural blueberry anthocyanins: A non-destructive monitoring system for the freshness of aquatic products with prospective smartphone compatibility

Abstract

Packaging plays a pivotal role in preserving food quality throughout processing and storage. This study developed a smart hydroxypropyl methylcellulose- κ-carrageenan- gelatin (H-K-G-B) film containing blueberry anthocyanins (BA) for freshness monitoring. The incorporation of BA significantly enhanced the film's antioxidant properties, with DPPH and ABTS radical scavenging capacities reaching 82.92 % and 86.44 %, respectively. The mechanical strength of H-K-G-B film was satisfactory, achieving tensile strength of 5.85 MPa and Young's modulus of 24.05 MPa, along with superior UV-vis light barrier performance. The H-K-G-B film exhibited high NH₃ sensitivity at 32.79 % and distinct color changes with pH response in alkaline environments (R² = 0.9502), which was successfully applied in salmon spoilage indication. Moreover, based on the significantly correlations (R² > 0.90) between chromatic parameters and quality parameters, including pH, TVB-N, and TBARS, a smartphone-based visual detection platform for real-time food freshness indication was established. So, this work provides a scientifically validated solution for intelligent food packaging.

Keywords: Freshness monitoring; Intelligent film; pH responsiveness.

Graphical abstract

Fig. 1

(a) Schematic diagram of preparation approach, (b) SEM images, (c) FTIR and (d) XRD spectra of H-K-G-B intelligent films.

Fig. 2

(a) Antioxidant properties, (b) light transmittance, (c) water vapor permeability, (d) thickness, (e) mechanical properties, and (f) swelling ratio of H-K-G-B intelligent films. (g) Photos and (h) weight loss degree of H-K-G-B intelligent films during degradation. (i) Cytotoxicity of H-K-G-B intelligent films. Noting: different lower-case letters represent significant differences within the same experimental group (P < 0.05).

Fig. 3

(a) Color response and (b) UV–vis spectra of BA solution under pH = 2.0–12.0 conditions. (c) Scheme of the pH-responsive structural interconversion between dominant forms of BA in aqueous solution.

Fig. 4

(a) Photos and color parameters (L*, a* and b* values) of H-K-G-B intelligent films under different pH conditions. (b) The relationship between ΔE of H-K-G-B intelligent films and pH values. (c) Color stability of H-K-G-B films.

Fig. 5

(a) Photos and (b) color alterations of H-K-G-B intelligent films with NH₃-response.

Fig. 6

(a) TVB-N, (b) pH and (c) TBARS of salmon meat at 4 °C and 25 °C for 14 days. (d) Photos of the application of H-K-G-B intelligent films in salmon meat freshness monitoring (0, 2, 4, 6 and 8 on the photos represent H-K-G, H-K-G-B 2, H-K-G-B 4, H-K-G-B 6, H-K-G-B 8 film, respectively). (e) ΔE value of H-K-G-B intelligent films during salmon meat storage. (f) Heatmap of the correlation of ΔE value of H-K-G-B 8 intelligent film and the food freshness indexes, including pH, TVB-N, and TBARS.

Fig. 7

(a) A demonstration of the conversion of H-K-G-B intelligent films image into color and freshness index information by a smartphone. The relationship between color information of H-K-G-B intelligent films and (b) pH, (c) TVB-N and (d) TBARS in actual application of salmon meat freshness monitoring, respectively.