Bilayer pH-sensitive colorimetric indicator films based on zein/gellan gum containing black rice (Oryza sativa L.) extracts for monitoring of largemouth bass (Micropterus salmoides) fillets freshness

Characterization, grass carp (Ctenopharyngodon idella) freshness monitoring and preservation effects of active films incorporated with Solanum nigrum L. anthocyanins

This study investigated the characterization, grass carp freshness monitoring and preservation effects of active films containing Solanum nigrum L. anthocyanins (SNA). Compared to the composition of SNA, the amounts of cyanidin, delphinidin, malvidin and rutin in the SNA composite film decreased, while those of quercetin, isorhamnetin and kaempferol increased. SNA was effectively integrated into the polyvinyl alcohol /fish gelatin (PVA/FG) film via hydrogen bonding but reduced the film's structure integrity and thermal stability. Interestingly, 0.2 % SNA improved the mechanical properties of the PVA/FG film, enhancing its responsiveness to pH fluctuations and NH3 environments. Whereas, PVA/FG-0.3 %SNA and PVA/FG-0.4 %SNA films exhibited stronger antioxidant capability and higher active compounds migration efficiency. The PVA/FG-0.2 %SNA film monitored grass carp freshness by transforming from pink to light pink, eventually becoming colorless. Meanwhile, the PVA/FG-0.3 %SNA film significantly inhibited increases in pH, total viable count, thiobarbituric acid reactive substance, and total volatile base nitrogen levels in grass carp.

An intelligent bilayer film based on blue honeysuckle berries and Artemisia Sphaerocephala Krasch. Gum for Cyprinus carpio preservation and indication

The demand for extended shelf life and food safety in the food industry continues to rise. At the same time, the environmental burden of traditional plastic packaging materials is becoming increasingly serious. Therefore, in this study, an intelligent bilayer film with a pH-sensitive inner indicator film based on Artemisia Sphaerocephala Krasch. Gum (ASKG) and blue honeysuckle berries anthocyanin (BHBA), and an antimicrobial outer film composed of polyvinyl alcohol (PVA) and cinnamon essential oil (CEO) were developed. SEM cross-sectional images showed a clear interface of the bilayer films, demonstrating the successful binding of the inner and outer layers; FTIR and X-ray results showed the binding and interaction of the components. The properties of the bilayer film were significantly enhanced with the increase of BHBA content. Compared to ASKG-BHBA film, the tensile strength of the bilayer film with 18 % anthocyanins increased by 143.66 %, elongation at break increased by 60.92 %, and showed excellent water resistance as well as water vapour barrier, thermal stability, free radical scavenging activity (increased by 14.7 %), and antimicrobial activity (inhibition circle diameter increased by 53.79 % and 57.98 %, respectively). In addition, the ASKG-BHBA and bilayer films exhibited excellent UV-vis light barrier, pH sensitivity and responsiveness to ammonia vapour. Freshness tests applied to Cyprinus carpio showed that the intelligent film could monitor the fish's freshness in real time and extended the shelf life by 1 to 3 days compared to the control. According to preliminary calculations, the cost of producing the bilayer film is about 0.1499 USD/piece. The bilayer film is expected to meet the market's dual demand for food safety and environmental protection and realize a wide range of applications in fresh food preservation and quality monitoring in the future.

A highly stable gellan gum/potato starch/anthocyanin smart film with ferulic acid co-pigmentation for monitoring fish freshness

A novel high stability pH-sensitive smart film (GGPS-R-FA) was prepared by using gellan gum (GG) and potato starch (PS) as the film-forming material, red cabbage anthocyanins extract (RCAE) as the indicator, and ferulic acid (FA) as the co-pigmentation agent. The enhancement effect of co-pigmentation on the stability of RCAE, as well as the performance and application of smart film were investigated. The RCAE co-pigmented with FA showed higher absorbance and greater thermal stability, as evidenced by the retention of anthocyanin content and thermodynamic parameters. The retention rates of anthocyanin content was increased from 24.59 % to 37.94 %. Structural characterization showed that molecular interactions protected the structure of anthocyanins and contributed to form a more stable film network. The EAB of the films was improved to 25.13 % and the opacity was increased to 5.02 A·mm-1. The co-pigmented films exhibited excellent color stability after co-pigmentation. The ∆E of GGPS-R-FA films was lower than 3 during 120 days of storage at 4 °C. The films exhibited a sensitive responsiveness to pH and ammonia. When the films were applied to monitor the fish's freshness, the color changes of GGPS-R-FA1 and GGPS-R-FA2 films represented a strong correlation with the spoilage indices of grass carp.

Development and evaluation of pH-sensitive Euryale ferox starch-based films containing nano-SiO2 and Chinese rose (Rosa chinensis) extract for freshness monitoring of chicken breast meat

In this study, smart films of EFS, EFS-SiO2 and EFS-SiO2-CRE were successfully developed by using Euryale ferox starch (EFS), nano-SiO2 and Chinese rose extract (CRE). The Chinese rose flower had a high content of anthocyanins (1.73 mg/g) and CRE exhibited different colors in varying pH buffers (2-13). The addition of nano-SiO2 decreased tensile strength (TS) (41.08 to 16.75 MPa) and elongation at break (EAB) (6.71 to 2.69 %) of the EFS film. Incorporation with CRE could significantly increase water vapor permeability (4.47 to 5.35 10-11 g m-1 s-1 Pa-1), TS (16.75 to 26.19 MPa) and EAB (2.69 to 4.62 %) of the EFS-SiO2 film. Incorporation of nano-SiO2 and CRE significantly enhanced the thermal stability and light barrier performance of the EFS film. The EFS-SiO2-CRE films showed excellent pH and ammonia sensitivities with different colors varying from red to blue. The EFS-SiO2-CRE-III film displayed strong antioxidant activity with a maximum DPPH scavenging rate of 96.54 ± 0.44 %. When employed for monitoring freshness of chicken breast meat, the EFS-SiO2-CRE-III film showed the most significant visible color changes at 24 h when the TVB-N content was 21.7 mg/100 g. Findings supported the application of this strategy in fabrication of the EFS-SiO2-CRE-III film for smart packaging.

Development of Zein-PEG400/PVA-Chitosan Bilayer Films for Intelligent Packaging

Zein exhibits excellent biodegradability, thermal stability, UV resistance, and water barrier properties, making it a promising candidate for food packaging applications. However, pure zein films suffer from brittleness and poor mechanical strength, which limit their practical use. In this study, a unique bilayer packaging film (ZP/P-C) was developed using a layer-by-layer solution casting technique, where hydrophobic zein was coated onto a polyvinyl alcohol and chitosan composite layer (P-C). Incorporating PEG400 into the zein layer improved the interfacial compatibility of the bilayer film, increasing its uniformity and toughness. The resulting bilayer films demonstrated enhanced mechanical properties, flexibility, and water vapor barrier performance. Specifically, the ZP7.5/P-C bilayer film showed an elongation at break of 68.74% and a modulus of elasticity of 187.19 MPa. It had a water vapor permeability of 6.60 × 10-11 g·m·m-2·s-1·Pa-1 and provided near-complete UV protection within the 200-350 nm range. Furthermore, an intelligent detection bilayer film was created by integrating anthocyanin extract into the zein layer. Adding anthocyanin improved the film's antioxidant properties and allowed it to respond colorimetrically to total volatile basic nitrogen. The bilayer film ZPBA1.0/P-C displayed an excellent antioxidant activity (45.8%) and remarkable color change (ΔE = 20.2) in response to ammonia, effectively indicating shrimp spoilage in 48 h (ΔE > 10). This investigation spotlights the potential of zein-based bilayer films in active and intelligent food packaging, offering innovative strategies to improve food safety and extend the shelf life of perishable goods.

A double-sided coating paper antibacterial indicator card based on polyvinyl alcohol/sodium carboxymethyl cellulose-anthocyanins and chitosan-halloysite nanotubes loaded essential oil to monitor fish freshness

This study developed a multifunctional paper-based freshness antibacterial indicator card by dual-sided coating on conventional filter paper. The indicator coating was composed of anthocyanins from purple cabbage, and polyvinyl alcohol and sodium carboxymethyl cellulose as substrates while the antibacterial coating contained halloysite nanotubes for loaded thyme essential oil and chitosan. FT-IR, XRD, and SEM analyses revealed that the components were well-mixed, and the paper was tightly bound to the coatings through hydrogen bonds. Additionally, the coating effectively filled the porous fiber gaps in the paper, significantly enhancing the mechanical properties of the paper. The tensile strength of the coated paper was enhanced from 14.28 MPa to a range of 42.25-47.71 MPa, and the bending resistance was increased from 0.35 N·mm to a range of 1.72-1.99 N·mm compared to the uncoated paper. The addition of anthocyanins provided excellent sensitivity to pH and ammonia for the indicator card. Furthermore, the coating including halloysite nanotubes for loaded thyme essential oil exhibited antimicrobial resistance against Escherichia coli and Staphylococcus aureus. When used on fresh carp, the antibacterial indicator card not only indicated the freshness of the carp but also extended the best before date of the fish meat by 1-2 days. The indicator exhibited the most pronounced color transformation and optimal freshness indication performance when the mass fraction of anthocyanins was 2 %.

Advancements in Gellan Gum-Based Films and Coatings for Active and Intelligent Packaging

Gellan gum (GG) is a natural polysaccharide with a wide range of industrial applications. This review aims to investigate the potential of GG-based films and coatings to act as environmentally friendly substitutes for traditional petrochemical plastics in food packaging. GG-based films and coatings exhibit versatile properties that can be tailored through the incorporation of various substances, such as plant extracts, microorganisms, and nanoparticles. These functional additives enhance properties like the light barrier, antioxidant activity, and antimicrobial capabilities, all of which are essential for extending the shelf-life of perishable food items. The ability to control the release of active compounds, along with the adaptability of GG-based films and coatings to different food products, highlights their effectiveness in preserving quality and inhibiting microbial growth. Furthermore, GG-based composites that incorporate natural pigments can serve as visual indicators for monitoring food freshness. Overall, GG-based composites present a promising avenue for the development of sustainable and innovative food packaging solutions.

A review on improving the sensitivity and color stability of naturally sourced pH-sensitive indicator films

Naturally sourced pH-sensitive indicator films are of interest for real-time monitoring of food freshness through color changes because of their safety. Therefore, natural pigments for indicator films are required. However, pigment stability is affected by environmental factors, which can in turn affect the sensitivity and color stability of the pH-sensitive indicator film. First, natural pigments (anthocyanin, betalain, curcumin, alizarin, and shikonin) commonly used in pH-sensitive indicator films are presented. Subsequently, the mechanisms behind the change in pigment color under different pH environments and their applications in monitoring food freshness are also described. Third, influence factors, such as the sources, types, and pH sensitivity of pigments, as well as environmental parameters (light, temperature, humidity, and oxygen) of sensitivity and color stability, are analyzed. Finally, methods for improving the pH-sensitive indicator film are explored, encapsulation of natural pigments, incorporation of a hydrophobic film-forming matrix or function material, and protective layer have been shown to enhance the color stability of indicator films, the addition of copigments or mental ions, blending of different natural pigments, and the utilization of electrospinning have been proved to increase the color sensitivity of indicator films. This review could provide theoretical support for the development of naturally sourced pH-sensitive indicator films with high stability and sensitivity and facilitate the development in the field of monitoring food freshness.

Frontier in gellan gum-based microcapsules obtained by emulsification: Core-shell structure, interaction mechanism, intervention strategies

As a translucent functional gel with biodegradability, non-toxicity and acid resistance, gellan gum has been widely used in probiotic packaging, drug delivery, wound dressing, metal ion adsorption and other fields in recent years. Because of its remarkable gelation characteristics, gellan gum is suitable as the shell material of microcapsules to encapsulate functional substances, by which the functional components can improve stability and achieve delayed release. In recent years, many academically or commercially reliable products have rapidly emerged, but there is still a lack of relevant reports on in-depth research and systematic summaries regarding the process of microcapsule formation and its corresponding mechanisms. To address this challenge, this review focuses on the formation process and applications of gellan gum-based microcapsules, and details the commonly used preparation methods in microcapsule production. Additionally, it explores the impact of factors such as ion types, ion strength, temperature, pH, and others present in the solution on the performance of the microcapsules. On this basis, it summarizes and analyzes the prospects of gellan gum-based microcapsule products. The comprehensive insights from this review are expected to provide inspiration and design ideas for researchers.

Development of pH-freshness smart label based on gellan gum film incorporated with red cabbage anthocyanins extract and its application in postharvest mushroom

Novel colorimetric films based on gellan gum (GG) containing red cabbage anthocyanins extract (RCAE) were prepared as pH-freshness smart labels for real-time visual detection of mushroom freshness. The GG/RCAE films had excellent pH and ammonia sensitivity. The GG/RCAE-0.2-0.3 films had the highest sensitivity to acetic acid. The SEM micrographs, AFM images, FT-IR and XRD spectra demonstrated that RCAE were successfully combined into the film-forming substrate. The incorporation of RCAE resulted in the increase of thermal stability, opacity and surface hydrophobicity of films. Meanwhile, the GG/RCAE-0.2 film exhibited stronger tensile strength and excellent color stability at 4℃. The color changes of GG/RCAE-0.2 film were visually easier to distinguish during the storage of mushroom. The results showed the GG/RCAE films could be used as pH-freshness smart labels to detect the freshness of fruits and vegetables.

Development of CO2-sensitive antimicrobial bilayer films based on gellan gum and sodium alginate/sodium carboxymethyl cellulose and its application in strawberries

To effectively extend the shelf life of fruits meanwhile facilitating consumers to judge their freshness, in this work, a double-layer multifunctional film combining CO2 sensitivity and antibacterial properties was successfully prepared by adding methyl red (MR), bromothymol blue (BTB) into gellan gum (GG) as the sensing inner layer, and doping tannic acid (TA) into sodium alginate with sodium carboxymethyl cellulose (CMC) as the antimicrobial outer layer, which was applied to the freshness indication of strawberries. Microscopic morphology and spectral analysis demonstrated that the bi-layer films were fabricated successfully. The mechanical characteristics, thermal stability, water vapor resistance, and antibacterial capabilities of the bilayer films improved as TA concentration rose. They exhibited noticeable color changes at pH = 2-10 and different concentrations of CO2. Application of the prepared films to strawberries revealed that the GG-MB@SC-6%TA film performed most favorably under 4 °C storage conditions, not only monitoring strawberry freshness but also retaining high soluble solids and titratable acidity, resulting in a slight decrease in hardness and weight loss. Therefore, taking into account all of the physical-functional characteristics, the GG-MB@6%TA film has a broad application prospect for intelligent food packaging.

Gellan Gum and Polyvinyl Alcohol Based Triple-Layer Films Enriched with Alhagi sparsifolia Flower Extract: Preparation, Characterization, and Application of Dried Shrimp Preservation

To meet the demand for biobased packaging and minimize the oxidation of dried aquatic goods during storage, we created a triple-layer film (TF) with antioxidant capacity. The film was produced using polyvinyl alcohol (PVA) as the protective layer, gellan gum (GG)/PVA composite incorporating Alhagi sparsifolia flower extract (AFE) as the anti-oxidative capability layer, and GG as the anti-oxidative capacity slow-release control layer. The TFs with different AFE additions were characterized and compared to a single-layer film (SF) made of the same material. The results demonstrate that adding AFE to films degraded their water vapour and oxygen barrier properties as well as their tensile strength, but increased their light barrier properties, elongation at break, and anti-oxidative capability. The three-layer structure increased the light, water vapour, and oxygen barrier qualities of films, as well as their slow-release anti-oxidative capability. The application experiment revealed that the inclusion of AFE might aid in the preservation of dried prawn quality. Using TF supplemented with 5 (w/v) AFE to package the dried shrimps reduced the TBARS value by 47.5%. Our research indicated that TFs containing AFE have a wide range of possible applications in dried shrimp preservation.

A review of food preservation based on zein: The perspective from application types of coating and film

The application of zein in food preservation was discussed from a unique perspective of application types, including coating and film. For the study of coating, edibility is considered because the coating adheres to the surface of food directly. For the study of film, plasticizers improve their mechanical properties, while barrier performance and antibacterial performance are achieved by nanoparticles; the incorporation of polyphenols is mainly due to their antibacterial and antioxidant properties; other biopolymers realize the complementarity between zein and biopolymers within films. In the future, the interaction between the edible coating and food matrix needs to be concerned. The mechanism of various exogenous additives and zein in the film should be noticed. Importantly, food safety and the possibility of large-scale application should be followed. Additionally, the intelligent response is one of the key development directions of zein-based film in the future.