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A novel bilayer colorimetric film incorporating polycaprolactone (PCL) with clitoria ternatea Linn anthocyanin (CA) via electrospinning was designed. The PCL nanofibers layer acted as a protective layer against harsh environments as the strong hydrophobic with the WCA (water contact angle) values of 101.79°. The PCL-CA layer worked as an indicator for its significant color changes for pH. The sensitivity test verified the ammonia cycler reversibility of the nanofibers is promising for re-use packaging. And the PCL/PCL-CA film was characterized as suitable WVP (water vapour permeability), and the lower velocity of water penetrating. Moreover, higher elongation at break (240.431%), and color stability were achieved. Besides, the film exhibited the color change from pale-blue to yellow-green response as an indication of shrimp spoilage (21 h). These results suggested the potential application of the PCL/PCL-CA film for a reusable freshness sensor tool in food packaging., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

This study designed a new type indicator with hydrophobic Polyvinylidene Fluoride (PVDF) film as a moisture prevent-layer. And the sensor layer was provided based on polyvinyl alcohol/Sodium alginate (PS) and Roselle anthocyanins (RAs). Physical properties, microstructure, and color stability of the bi-layer indicator have been investigated. The Water contact angle (WCA) of PS/RAs/ PVDF film (PSRF) was 108.85°, which can be considered as an excellent hydrophobic surface. The lowest Water Vapor Permeability (WVP) value of PSRF exhibited a good barrier property for moisture. Therefore, PSRF film was used to monitor the griskin freshness. The Total volatile basic nitrogen (TVB-N) level was increased to 18.02 mg/100 g at 72 h, and the color of the indicator presented visible color changes. The acquired results revealed a good correlation between TVB-N, pH and color change of the indicator. The research indicated that PSRF indicator has increasing potential application on food intelligent packaging., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

In the present study, two pH-sensitive bilayer films were developed and compared. Agar matrix incorporated with ZnO nanoparticles (NPs) or TiO 2 NPs were combined with the infrastructure of a κ-carrageenan-Clitoria ternatea Linn anthocyanin (CA-CTLA) layer, denoted as AG-ZnO/CA-CTLA film and AG-TiO 2 /CA-CTLA film, respectively. The CA-CTLA layer was defined as the sensing layer, whereas the AG-TiO 2 (or AG-ZnO) layer was the protective layer that enhanced the mechanical properties and colour stability. The AG-TiO 2 /CA-CTLA film displayed superior UV-vis light barrier property, pH sensitivity, and physical properties. The film's elongation at break and water vapour permeability were 57.08%, and 2.72 × 10 -6  g.m -1 .h -1 .pa -1 , respectively. Notably, the AG-TiO 2 /CA-CTLA film possessed the highest UV-vis light barrier properties, and the transmittance was close to 0 in the UV region. Furthermore, these films exhibited visual colour changes in the buffer solution (pH 2.0-12.0), ammonia vapour (80 M), and pork spoilage trials. Therefore, the bilayer films have promising properties for food packaging, especially the AG-TiO 2 NPs/CA-CTLA film., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Design and fabrication of an ammonia sensor operating at room temperature based on pigment-sensitized TiO2 films was described. TiO2 was prepared by sol-gel method and deposited on glass slides containing gold electrodes. Then, the film immersed in a 2.5×10(-4)M ethanol solution of cyanidin to absorb the pigment. The hybrid organic-inorganic formed film here can detect ammonia reversibly at room temperature. The relative change resistance of the films at a potential difference of 1.5V is determined when the films are exposed to atmospheres containing ammonia vapors with concentrations over the range 10-50 ppm. The relative change resistance, S, of the films increased almost linearly with increasing concentrations of ammonia (r=0.92). The response time to increasing concentrations of the ammonia is about 180-220 s, and the corresponding values for decreasing concentrations 240-270 s. At low humidity, ammonia could be ionized by the cyanidin on the TiO2 film and thereby decrease in the proton concentration at the surface. Consequently, more positively charged holes at the surface of the TiO2 have to be extracted to neutralize the adsorbed cyanidin and water film. The resistance response to ammonia of the sensors was nearly independent on temperature from 10 to 50°C. These results are not actually as good as those reported in the literature, but this preliminary work proposes simpler and cheaper processes to realize NH3 sensor for room temperature applications., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Anthocyanins-based colorimetric volatile amines sensors have recently received great attention for monitoring meat and fish freshness. However, most of the sensors suffered from anthocyanins leaching problems in humid packaging environments, severely limiting their indication ability. The present study developed a hydrogel-in-oleogel bigel to protect anthocyanins from leaching. The internal hydrogel was composed of water, agar and purple sweet potato anthocyanins (PSPA), and the external oleogel was made up of sunflower oil, beeswax and glyceride monooleate (GMO). The agar concentration and water-to-oil-phase volume ratio (W/O) were optimized to be 1.0% and 2:8, respectively. The optimal pH value of hydrogel was determined to be 6.50, taking into consideration of the gas sensitivity and color stability of the bigel. The bigel was extruded onto polyvinylidene fluoride (PVDF) film through a 3D printing method to form the composite film. The results of the study revealed that PVDF-bigel composite film showed good stability in water, indicative of strong anti-leaching properties. Meanwhile, the PVDF-bigel film was sensitive to trimethylamine (TMA) with a limit of detection of 2.52 μM. The PVDF-bigel film was subjected to in-situ and real-time monitor beef and salmon freshness. The film exhibited a red-to-purple color change upon reacting with volatile amines generated from beef and salmon. Henceforth, this study presented a new method to develop anthocyanins-based colorimetric gas sensors for intelligent food packaging. [Display omitted] • A hydrogel-in-oleogel bigel containing anthocyanins was developed. • The bigel with a W/O ratio of 2:8 showed good rheological properties for 3D printing. • The bigel showed good color stability in water, indicating its anti-leaching ability. • The bigel was sensitive to TMA with LOD of 2.52 μM. • The bigel used to monitor beef and salmon freshness showed visible color changes. [ABSTRACT FROM AUTHOR]

• Bilayer films were developed using agar, anthocyanins, gellan gum and TiO 2. • TiO 2 improved the illumination stability of the film. • Gellan gum-TiO 2 contributed to the electrochemical writing on the film. • The bilayer film was sensitive to NH 3 , trimethylamine and dimethylamine. • The bilayer film showed color changes during spoilage of pork and silver carp. Amine-responsive bilayer films were developed by using agar (AG), anthocyanins (AN), gellan gum (GG) and TiO 2 nanoparticles for visual monitoring of meat spoilage. The AG-AN layer worked as the sensing layer to volatile amines, while GG-TiO 2 layer served as the light barrier layer and simultaneously the conducting layer to improve the illumination stability and electrochemical writing ability of the AG-AN layer, respectively. The Scanning electron microscopy (SEM) images and X-ray diffraction (XRD) spectra indicated the successful fabrication of bilayer films. Illumination experiments showed that the incorporation of TiO 2 in the GG-TiO 2 layer significantly improved the illumination stability of AN in the AG-AN layer. Meanwhile, electrochemical writing process could be easily conducted on the AG-AN layer in the presence of GG-TiO 2 layer, indicating the feasibility of ink-free printing on bilayer biopolymer films. The AG-AN/GG-2%TiO 2 film presented a limit of detection of 0.018 mM to trimethylamine (TMA), a typical basic gas generated during meat spoilage. Based on its good illumination stability and sensing ability to basic gases, the AG-AN/GG-2%TiO 2 film exhibited rose red-to-green color changes along with the spoilage of pork and silver carp, indicating its great potential for monitoring meat spoilage in intelligent food packaging. [ABSTRACT FROM AUTHOR]