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

Visual indicator bi-layer films were manufactured incorporating kappa-carrageenan, butterfly pea flower anthocy-anin, varying Nano-titanium dioxide (TiO2) content and agar for Penaeus chinensis (Chinese white shrimp) freshness detection. The kappa-carrageenan-anthocyanin (CA) layer served as indicator, while the TiO2-agar (TA) layer functioned as the protective layer to improve the photostability of film. The bi-layer structure was char-acterized 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 x 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 TiO2 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 Delta E 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 (R2 = 0.8739).