A visual bi-layer sensor based on Agar/TiO2/butterfly bean flower anthocyanin/κ-carrageenan with photostability for monitoring Penaeus chinensis freshness.

Visual indicator bi-layer films were manufactured incorporating κ-carrageenan, butterfly pea flower anthocyanin, varying Nano‑titanium dioxide (TiO 2) content and agar for Penaeus chinensis (Chinese white shrimp) freshness detection. The κ-carrageenan-anthocyanin (CA) layer served as indicator, while the TiO 2 -agar (TA) layer functioned as the protective layer to improve the photostability of film. The bi-layer structure was characterized by scanning electron microscopy (SEM). The TA2-CA film had the best tensile strength with a value of 17.8 MPa and the lowest water vapor permeability (WVP) value of bi-layer films was 2.98 × 10−7 g.m−1.h−1.pa−1. The bi-layer film protected anthocyanin against exudation when immersed in aqueous solution of varying pH. The TiO 2 particles filled the pores of the protective layer, increasing the opacity from 1.61 up to 4.49 significantly improving the photostability with a consequent slight color change under illumination of UV/visible light. Under UV irradiation, the TA2-CA film had no significant color change with a ΔE value of 4.23. Finally, the TA2-CA films showed an obvious color change from blue to yellow green in the early stages of Penaeus chinensis putrefaction (≤48 h) then the color change and Penaeus chinensis freshness were well correlated (R 2 = 0.8739). [Display omitted] • Visual indicator bi-layer film was manufactured with indicator and protective layer. • The TA protective layer effectively increased the photo-stability of the films. • The TA-CA bi-layer films present obvious color changes to ammonia and pH. • The TA2-CA films were potential in monitoring Penaeus chinensis freshness. [ABSTRACT FROM AUTHOR]