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The aim of this study was to prepare a novel pH-sensitive smart film based on the addition of purple garlic peel extract (PGE) and TiO2 nanoparticles in a sodium alginate (SA)/polyvinyl alcohol (PVA) matrix to monitor the freshness of beef. FT-IR spectroscopy revealed the formation of stronger interaction forces between PVA/SA, PGE, and TiO2 nanoparticles, which showed good compatibility. In addition, the addition of PGE improved the tensile strength and elongation at break of the composite film, especially in different pH environments, and the color response was obvious. The addition of 1% TiO2 nanoparticles significantly improved the mechanical properties of the film, as well as the light barrier properties of the film. PGE could effectively be uniformly dispersed into the composite film, but it also had a certain slow-release effect on the release of PGE. PGE had high sensitivity under different pH conditions with rich color changes, and the color showed a clear color change from red to yellow-green when the pH increased from 1 to 14. The same change was observed when it was added to the film. In particular, by applying this film to the process of beef preservation, we judged the freshness of beef by monitoring the changes in the TVB-N value and pH value during the storage process of beef and found that the film showed obvious color changes during the storage process of beef, from blue (indicating freshness) to red (indicating non-freshness), and finally to yellow-green (indicating deterioration), which indicated that the color change of the film and the freshness of the beef maintained a highly consistent. [ABSTRACT FROM AUTHOR]

Smart film is widely used in the field of food packaging. The smart film was prepared by adding anthocyanin-rich Robusta coffee peel (RCP) extract into a chitosan (CS)–glycerol (GL) matrix by a solution-casting method. By changing the content of RCP (0, 10%, 15% and 20%) in the CS–GL film, the related performance indicators of CS–GL–RCP films were studied. The results showed that the CS–GL–RCP films had excellent mechanical properties, and CS–GL–RCP15 film maintained the tensile strength (TS) of 16.69 MPa and an elongation-at-break (EAB) of 18.68% with RCP extract. CS–GL–RCP films had the best UV-vis light barrier property at 200–350 nm and the UV transmittance was close to 0. The microstructure observation results showed that CS–GL–RCP films had a dense and uniform cross section, which proved that the RCP extract had good compatibility with the polymer. In addition, the CS–GL–RCP15 film was pH-sensitive and could exhibit different color changes with different pH solutions. So, the CS–GL–RCP15 film was used to detect the fermentation process of pickles at 20 ± 1 °C for 15 days. The pickles were stored in a round pickle container after the boiling water had cooled. The color of the CS–GL–RCP15 film changed significantly, which was consistent with the change of pickles from fresh to mature. The color of the smart film changed significantly with the maturity of pickles, and the difference of ΔE of film increased to 8.89 (15 Days), which can be seen by the naked eye. Therefore, CS–GL–RCP films prepared in this study provided a new strategy for the development of smart packaging materials. [ABSTRACT FROM AUTHOR]

In this study, blue corn extract (BCE) was added to a corn starch, polyvinyl alcohol (PVA) based smart packaging indicator film. Characterization of physical properties of films by tensile test and color difference test. The color changes of BCE and corn starch/PVA/BCE composite films were investigated in the pH range of 1–14. Scanning electron microscopy images showed good compatibility of BCE with the substrate. BCE significantly increased the tensile strength, elongation at break and water content of the films (p < 0.05). The corn starch/PVA/BCE films had good color stability. The addition of BCE had no significant effect on film thickness (p < 0.05). The corn starch/PVA/BCE film underwent a significant change from red to dark purple during the film application for the preservation and storage of tilapia. The results showed that this pH sensitive film has the potential to indicate the shelf life of tilapia. Practical Application: Smart pH indicator films were prepared by mixing different ratios of blue corn extract with corn starch/PVA substrates. The effects of different ratios of BCE on the physical properties and pH sensitivity of the composite membranes were investigated. During the storage of tilapia, the composite membranes showed a clear change from red to dark purple. [ABSTRACT FROM AUTHOR]

Summary: This study aimed to develop a novel pH‐sensitive intelligent film for monitoring minced beef freshness based on chitosan/sodium alginate (CS–SA) and coffee peel anthocyanin (CPA). The different CPA content effects on the internal structure, physical properties and pH sensitivity of the CS–SA films were investigated. The results showed low contents of CPA (≤2%) could be evenly distributed within the CS–SA matrix with good compatibility. The addition of CPA significantly improved the physical properties and pH sensitivity of the CS–SA films. The CS–SA film containing 2% CPA (CS–SA–CPA2) showed the best tensile strength, water vapour barrier performance and most noticeable colour change. Moreover, this film exhibited good colour stability after 120 days. The CS–SA–CPA2 film changed colour from light yellow to brown to dark brown during minced beef storage, successfully indicating freshness. Therefore, the CS–SA–CPA2 film has the potential to be a pH‐sensitive material for monitoring minced beef freshness. [ABSTRACT FROM AUTHOR]

An intelligent pH indicator film was prepared by mixing cassava starch, polyvinyl alcohol (PVA), and natural anthocyanin extracted from grape skin (GSE) and mangosteen rind (MRE). The effects of GSE and MRE on the physical, structural, and pH‐sensing performance of composite films were studied. Scanning electron microscope results showed that the microstructure of film had little difference when the anthocyanin extracts were incorporated into the polymer matrix. A significant (p <.05) effect of GSE and MRE on the tensile strength, moisture content, and elongation at the break of the films were observed. The two indicator films could respond to different pH values and showed good color stability. During the storage of pork, the cassava starch/PVA/GSE film showed a visible color variation from pink, blue, purple to yellow, while the cassava starch/PVA/MRE film showed color variation from light yellow, bright yellow, green to dark green. The result indicated that the two films could be used to monitor pork freshness for intelligent pH indicator packaging. Novelty impact statement: Using fruit waste to extract anthocyanin.Indicator film has good color stability, and the color change was obvious at different pH values.The color of the indicator film changed obviously in the process of indicating the freshness of pork. [ABSTRACT FROM AUTHOR]

In this research, pH-sensitive films were prepared based on gelatin, chitosan, and nanocellulose as film matrix, anthocyanins from hawthorn (Crataegus scabrifolia) fruit (0, 10, 15, and 20%) as natural pigments. The films were evaluated by thickness, moisture content, swelling property, water vapor permeability, mechanical property, UV–Vis light barrier property, microstructure, and color stability of films. The color of hawthorn fruit extract was distinctly different from pH 1 to pH 14. Scanning electron microscope analysis confirmed the biocompatibility between film matrix and hawthorn fruit extract. Fourier transform infrared spectra confirmed the structural changes in polymer matrix and anthocyanins. Furthermore, the pH-sensitive film showed evident color changes from red–purple (fresh), light grey (use soon), to yellow-green (spoiled) when applied to indicate the freshness of shrimp stored under 4 ± 1 °C, before the TVB-N value slowly increased to exceed the limit value (20 mg/100 g) on day 6. The results suggested that the developed films could be used to indicate the changes of food quality. [ABSTRACT FROM AUTHOR]

To monitor the freshness of chicken, a pH-sensitive film based on sodium alginate, gelatin, and plum peel extract (SGPE) was created. Thickness, color, water contact angle, mechanical characteristics, water content, water vapor transmission, light transmission, and pH sensitivity were used to evaluate the performance of the film sample. SEM and FTIR graphs demonstrated that adding plum peel extract made the SGPE film's internal structure more denser and increased its mechanical property, while decreasing the water contact angle, water content, and WVP value. The color of the SGPE15 film clearly changed from red to yellow-green in various buffer solutions (pH = 1–14), demonstrating more pH sensitivity than the SG, SGPE5, and SGPE10 films. On day 6, when checking the freshness of chicken kept at 4 °C, the SGPE15 film's color changed from orange-pink to yellow-green with TVB-N level beyond the allowable limit (15 mg/100 g). The result revealed that the SGPE film might be applied to monitor the freshness of chicken breast flesh. • Natural anthocyanin from plum peel extract was used to fabricate indicator film. • The color change of anthocyanin from plum peel extract was obvious. • Plum peel extract led to the internal structure of pure SGPE film much denser. • Plum peel extract improved the mechanical property and barrier property. • The SGPE film showed an evident visible color variation during chicken storage. [ABSTRACT FROM AUTHOR]