Intelligent pH indicator film composed of agar/potato starch and anthocyanin extracts from purple sweet potato

Edible blueberry anthocyanin-loaded soybean protein nanofibers/sodium alginate hydrogel beads: Freshness detection of high protein drinks

In this study, blueberry anthocyanins were embedded in soybean protein nanofibers/sodium alginate hydrogel (SNF/SA) to prepare an edible pH-responsive chromogenic hydrogel bead for freshness monitoring of milk, soybean milk and dual protein drinks. The results showed that the encapsulation rate of blueberry anthocyanins was 87.43 %. The loading of blueberry anthocyanins achieved the pH-response color development of SNF/SA hydrogel beads. SS/B3 hydrogel beads (SNF/SA loaded with 0.1 g anthocyanins) showed good color stability when stored in different environments for 96 h. When the SS/B3 hydrogel beads were used for detecting the protein drinks freshness, fresh drinks and spoiled drinks could be clearly distinguished by color of hydrogel beads. In addition, SS/B3 hydrogel beads promoted protein digestibility of protein drinks and protected anthocyanins from degradation in the stomach environment. Therefore, the hydrogel bead was accessible and edible, it could provide a possibility for monitoring the quality changes of fresh protein drinks.

Development of pH-sensitive colorimetric bioindicator antimicrobial films from oak tree acorn starch, red onion peel extract and methyl cellulose for freshness monitoring of chicken meat

The research on finding alternative natural and inexpensive materials for the development of biodegradable intelligent food packaging materials is increasing day by day to reduce plastic waste in the environment. In this study, new oak tree acorn starch-based films (S) with pH-sensitive and antimicrobial property were developed using oak tree acorns, quercetin (QUE) extract obtained from red onion peel and ZnO nanoparticles and their physicochemical, mechanical, thermal and barrier properties were compared with those of methyl cellulose-based films. S-QUE film having colorimetric pH-indicator property showed an obvious color variation from pink to green/yellow at different pH values (pH 1-12). Compared to S film, the maximum tensile stress and maximum tensile strain values of the S-QUE film increased by 93.34 % and 296.56 %, respectively. The presence of QUE extract in the film matrix increased the thermal stability of films and ZnO nanoparticles decreased it. The use of QUE extract and ZnO nanoparticles in film formulation led to an improvement in the water vapor barrier properties of films. The effectiveness of S-QUE and S-QUE-ZnO films in monitoring the spoilage of chicken meat was tested. These films showed visible color responses as the chicken meat spoiled.

Designing the pH-sensitive indicator based on starch nanoparticle with bromocresol green for monitoring meat spoilage

The starch nanoparticle, combined with bromocresol green (BCG), served as a pH-sensitive indicator to monitor meat quality throughout an 8-day refrigerated storage period. The meat samples were sealed in package which the pH-sensitive indicator attached to the interior part of packaging lid. The changes in meat quality were evaluated by total volatile base nitrogen (TVBN), pH, total viable count (TVC), sensory analysis, and color in interval of 0, 3, 5, 7, and 8-days storage at 4°C. Initial TVBN values were recorded at 19.6 mg/100 g, increased to 26.6 mg/100 g by the end of storage period. The pH value was significantly increased after 8 days storage at 4°C. The observed color variation in the indicator from yellow to blue was attributed to the concurrent increases in TVBN, TVC, and pH. The indicator color changes had significant correlation with analyzed chemical quality of stored meat. Therefore, the designed BCG pH-sensitive indicator could be effective in monitoring the meat spoilage during storage.

Flexible and Stretchable Electrochemical Sensor Merging the Multifunction of Monitoring Movement and Rapid Visual Signal Transmission

Noninvasive detection sensors for comfort and moisture absorption are popular for personalized health monitoring, yet integrated sensors that enable the on-demand detection of both physical and chemical indexes remain significantly challenging. Herein, we report a multifunctional fiber-based flexible sensing yarn for improved electrochemical and resistance sensing performance for in situ sweat activating and monitoring of body motion as well as the distinct color variation derived from the pH of sweat. The core-shell structure of the composite yarn (TSY) consists of a core layer of direct wet-spun twisted polyurethane fibers mixed with carbon black and a hydrophilic fiber layer of conductive zinc wires and colored lyocell fiber through the braiding method. The internal confined space between the core-shell layers can induce ion enrichment in sweat, enhancing the electrochemical sensing ability in capturing 0.5 μL of sweat, while the space-separated design can further isolate the interference so that pH and motion can be analyzed. Additionally, the colored hydrophilic lyocell fiber can transmit visual signals by the variance of color derived from the characterization of natural dyes in the process of adsorption of sweat. The designed TSY represents a promising integrated system capable of real-time monitoring of the chemical composition of sweat and the exercise conditions of movement.

Effect of different modified potato starch on starch-based films containing ZIF-67@thymol

Zeolite imidazolate framework-67 (ZIF-67) was used to encapsulate thymol (THY) to improve the properties of potato starch films. The effect of different modified potato starches (acetate starch (AS), hydroxypropyl di-starch phosphate (HDSP), oxidized hydroxypropyl starch (OHS), and acetylated di-starch phosphate (ADSP)) on the film properties was investigated. The results showed that the modified potato starch film had better water resistance, mechanical property, and water vapor barrier than the natural potato starch film. Scanning electron microscopy observations showed that the smoothness of the modified film was advanced. Notably, the OHS film had the best oxidation resistance activity of 76.93 % compared to the other four films. Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) were significantly inhibited in all potato starch films enhanced with ZIF-67@THY. Therefore, starch-based films incorporating ZIF-67@THY have a broad application prospect in food packaging.

Development and application of a time-temperature hydroxyethyl cellulose ink based on Clitoria ternatea L. blue petals anthocyanin and N-Hydroxyphthalimide for food freshness monitoring

A novel, sustainable time-temperature indicator (TTI) ink based on natural pigments is introduced for food freshness monitoring. The ink, composed of hydroxyethyl cellulose (HEC), Clitoria ternatea anthocyanin, and N-hydroxyphthalimide (NHPI), was applied to art paper using screen printing. The inks were characterized through FT-IR, particle size analysis, and rheological measurements, with optimal performance achieved at Clitoria ternatea anthocyanin to NHPI ratios of 9:1 and 7:1. The color change of the ink followed the Arrhenius equation, correlating with food degradation activation energies ranging from 0 to 75 kJ/mol. The ink was applied to monitor pork freshness, demonstrating high sensitivity and accuracy in tracking food quality. This TTI ink offers a cost-effective, environmentally friendly solution for food freshness assessment, with potential applications in reducing food waste and enhancing consumer confidence in food safety.

Sodium alginate/poly (vinyl alcohol) active films incorporated with Chrysanthemum leaves extract as an eco-friendly approach to extend the shelf life of green chilies

Recently, biodegradable packaging materials have received significant prominence in the food sector. Herein, chrysanthemum leaves extract (CLE), integrated sodium alginate (SA) and polyvinyl alcohol (PVA) active films were prepared and their physicochemical and multifunctional properties were evaluated for use in green chili packaging. FTIR and SEM results confirmed favorable interaction and uniform dispersion of CLE in the SA/PVA blend film. Addition of CLE to the SA/PVA matrix considerably lowered surface wettability (∼61 %), water solubility (∼28 %), moisture-binding (∼27 %), water vapor transmission and oxygen permeability (∼28 %). CLE-loaded active film demonstrated higher tensile strength (29.06 ± 0.46 MPa), UV light barrier capabilities and significant antimicrobial activity against foodborne pathogens. Additionally, it had an adequate antioxidant capacity of (∼46 %) compared to the control film without CLE. In the study of green chili packaging, the active film containing a more significant amount of CLE limited the weight loss, suppressed microbial growth and retained the polyphenolic and chlorophyll content of the chili. Compared to polyethylene (PE), the fabricated active film displayed a far better packaging capability and extended the shelf life of green chili for up to 10 days. Hence, the fabricated active films were suitable for biodegradable packaging applications.

Development of Plasma-Treated Corn-Starch-Based Film Incorporated with Acerola and Grape Pomace Extract Possessing pH-Sensing Capability

This study explores the development of biodegradable starch-based films treated with dielectric barrier discharge (DBD) plasma and incorporated with acerola residue and grape pomace extracts. The primary aim was to enhance the films' physicochemical properties and introduce pH-sensing capabilities. Plasma treatment at 200 Hz for 20 min modified the films' amylose content (by 13.2%), solubility (by 13.3%), contact angle (by 12.7%), moisture content (by 14.2%), and surface morphology. The addition of the extracts changed the short-range ordered structure parameters of the films (by 111.4%), solubility (by 11.1%), moisture content (by 18.4%), and water vapor permeability (by 6.1%). The films with acerola residue and grape pomace extracts exhibited good colorimetric responses for pH indication. The films with acerola residue extract tended to intensify the yellowish color, while those with grape pomace extract showed more significant color changes varying from purple to green. Integrating natural pigments like anthocyanins from grape pomace and carotenoids from acerola improved the films' functional properties and provided a visual indication of food freshness through pH changes.

Transforming Agricultural Waste from Mediterranean Fruits into Renewable Materials and Products with a Circular and Digital Approach

The Mediterranean area is one of the major global producers of agricultural food. However, along the entire supply chain-from farming to food distribution and consumption-food waste represents a significant fraction. Additionally, plant waste residues generated during the cultivation of specific fruits and vegetables must also be considered. This heterogeneous biomass is a valuable source of bioactive compounds and materials that can be transformed into high-performance functional products. By analyzing technical and scientific literature, this review identifies extraction, composite production, and bioconversion as the main strategies for valorizing agricultural by-products and waste. The advantages of these approaches as well as efficiency gains through digitalization are discussed, along with their potential applications in the Mediterranean region to support new research activities and bioeconomic initiatives. Moreover, the review highlights the challenges and disadvantages associated with waste valorization, providing a critical comparison of different studies to offer a comprehensive perspective on the topic. The objective of this review is to evaluate the potential of agricultural waste valorization, identifying effective strategies while also considering their limitations, to contribute to the development of sustainable and innovative solutions in Mediterranean bioeconomy.

Egg white protein‑sodium alginate smart labels based on pH-driven method and nonphase change 3D printing in mackerel freshness response

The smart labels prepared via the casting method and molten 3D printing method have a long heating time at high temperature and a dense network structure, resulting in a decrease in the color response ability of the labels. Therefore, this study uses a nonphase change foam 3D printing method with a shorter heating time to improve the color sensitivity of smart labels. By the pH driving method, the blending and pregelation of sodium alginate (Alg) can extend the drainage time of the interfacial film to the maximum extent, thus further improving the foam stability of egg white protein (EWP) and endowing the interfacial adsorption layer with better flexibility and fluidity. The pregelled Alg-EWP foam has good 3D printing adaptability, shows obvious shear thinning behavior, and has excellent shear recovery and creep recovery properties. The 3D-printed smart label has significantly higher swelling rate (275 % → 400 %), porosity (19.86 % → 42.86 %) and phenolic retention rate (55.51 % → 97.26 %). In addition, the sensitivity of the smart labels prepared via foam 3D printing significantly increased, indicating mackerel freshness. Therefore, the method of nonphase-change foam 3D printing provides a new strategy for preparing smart labels with increased porosity and color sensitivity.

Preparation and Characterization of Antioxidative and pH-Sensitive Films Based on κ-Carrageenan/Carboxymethyl Cellulose Blended with Purple Cabbage Anthocyanin for Monitoring Hairtail Freshness

Developing pH-sensitive materials for real-time freshness monitoring is critical for ensuring seafood safety. In this study, pH-responsive indicator films were prepared by incorporating purple cabbage anthocyanin (PCA) into a κ-carrageenan/carboxymethyl cellulose (CA/CMC) matrix via solution casting, with PCA concentrations of 2.5%, 5.0%, 7.5%, and 10% (w/w). The films exhibited remarkable pH sensitivity, with distinct color changes across pH 2.0-11.0. Incorporating PCA enhanced film crystallinity, antioxidant properties, and opacity while reducing water vapor transmission (WVP). High PCA content resulted in rougher morphology, lowering tensile strength (TS) but improving elongation at break (EB). The indicator film had good environmental stability, and the color difference was not visible after 10 days in the dark and 4 °C conditions. The CA/CMC/PCA-10% film showed the most pronounced pH-responsive color changes, transitioning from purple to green as hairtail freshness deteriorated. This innovative approach highlights the potential of CA/CMC/PCA films as reliable, eco-friendly indicators for real-time seafood freshness monitoring, offering significant advancements in smart packaging technology.

Smart pH-sensitive indicators based on rice starch/pectin/alginate loading Lambrusco pomace extract and curcumin to track the freshness of pink shrimps

This research is focused on the formulation and testing of green visual pH-sensitive indicators based on natural extracts from Curcuma Longa (CUR) and Lambrusco wine pomace (LAM), an Italian wine variety, incorporated into rice starch/pectin/alginate matrixes for non-destructively detecting shrimps freshness in real-time. The effect of the mixed indicators and their synergic combination on the properties and performances of indicators was investigated. Both the extracts and their combination showed pronounced pH responsiveness. Films were widely characterized in terms of morphological, barrier, spectroscopic, thermal and mechanical properties. The presence of extracts slightly reduced the transparency of the films while the film with both the extracts exhibited the highest Young's modulus (14.17 MPa), lowest moisture content (27.67 %) and a WVP value (0.79 g m m-2 s-1 Pa-1) intermediate between the Lambrusco extract loaded film and the curcumin based one. Moreover, the pH-sensitive systems showed a noticeable antioxidant activity (96 % for LAM/CUR film) and enhanced antibacterial activity toward E. coli and S. aureus compared to pristine films. Besides, the mixed indicator-based film showed high sensitivity to ammonia (68 %) determining an ΔE value easily detectable by the human eye. Finally, the films were applied as cheap visual indicators for monitoring the freshness of packaged fresh shrimps over time stored at T = 4 °C and T = 25 °C through the colourimetric variation induced by pH changes. The TVB-N value, which was correlated to the microbial count for shrimps over time, reached the rejection limit at 33 h for T = 25 °C and 54 h for T = 4 °C. The colour changes were recorded simultaneously and the turning to deeper colours indicated the decomposition of proteins to organic amines and the spoilage of food. Results show that the produced films provide easily detectable colour changes during food spoilage proving that, being fabricated from natural sources, they represent novel and sustainable tools for multi-purpose intelligent food packaging applications.

Recent advances in research on biomass-based food packaging film materials

Although traditional petroleum-based packaging materials pose environmental problems, biodegradable packaging materials have attracted extensive attention from research and industry for their environmentally friendly properties. Bio-based films, as an alternative to petroleum-based packaging films, demonstrate their significant advantages in terms of environmental friendliness and resource sustainability. This paper provides an insight into the development of biomass food packaging films such as cellulose, starch, chitosan, and gelatine, including their properties, methods of preparation (e.g., solution casting, extrusion blow molding, layer-by-layer assembly, and electrostatic spinning), and applications in food packaging. Through these preparation methods, the paper analyzes how the properties of the films can be effectively tuned and optimized to meet specific packaging needs. It was found that biomass film materials for food packaging not only possess functional properties such as antimicrobial, preservation, and indication, but also that their continued material innovation and technological improvements offer promising prospects for their use in commercial applications. These advances could help advance the global sustainable development goals, while showing great potential for improving food safety and extending shelf life. Future research will further explore new functions and applications of biomass films, providing additional solutions for environmental protection and sustainability.

Intelligent color changing packaging film based on esterified starch and black rice anthocyanins

Intelligent packaging film has received more and more attention because it can help consumers obtain more intuitive information about the packaging, provide better preservation and advanced convenience. In this study, black rice anthocyanin (BRA) was added into composite film formed by starch (S) and esterified starch (ES). As the BRA content increased, the thickness and the total color difference of the S/ES-BRA film increased. The opacity of S/ES-BRA film decreased relative to that of the film without BRA, but increased with the increase of anthocyanin. Compared with S/ES film, the elongation at break of S/ES-BRA0.5 film increased from 33.1 % to 45.4 %, and the tensile strength decreased from 7.3 to 5.8 MPa. S/ES-BRA film had response to different pH values and underwent color changes in different buffer solutions. Intelligent color changing packaging film will used to monitor food quality, water quality and soil properties.

Starch-pectin smart tag containing purple carrot peel anthocyanins as a potential indicator of analogous meat freshness

Smart films of starch/pectin and purple carrot peel (PCP) containing anthocyanins were developed, characterized, and used as pH-responsive tags to monitor plant-based chicken analogous. This study innovates by incorporating PCP in the film solution both as an extract and as a powder, and the resulting tags were applied to a plant-based food. PCP powder <100-mesh was directly incorporated into the film-forming suspension. For powder >100-mesh, two extracts were tested: an aqueous solution and a 1 % NADES solution added to the film-forming suspension. Quantification of PCP anthocyanins by HPLC showed a higher extraction under acidic conditions (1664 mg C3G equivalents 100 g-1). Films with PCP presented greater light protection. Films with 15 % and 25 % PCP and those with added extract showed better tensile strength (3.0-3.6 MPa), elongation at break (16-20 %) and a water contact angle of 52°. All films responded to pH variations (1 to 14) and ammonia vapor and showed ΔE* values >5. After 3 days, films used as smart tags monitoring chicken analogous presented noticeable color differences for PCPNADES (55 ± 8) and 15%PCP (40 ± 1). PCP showed strong potential as a pigmenting agent in films, especially as an aqueous extract with NADES for use as pH-responsive tags in chicken analogous.

Application of visual intelligent labels in the assessment of meat freshness

With the increasing demand for meat products, the evaluation and real-time monitoring of its freshness has become one of the focuses of related industry research. Conventional freshness detection methods, including sensory evaluation, microbial experiments, and determination of physicochemical indicators, are time-consuming, low sensitivity, and destructive, so there is an urgent need to develop a convenient, intuitive, and inexpensive detection method. As a representative of smart packaging, visual intelligent labels can realize real-time perception and monitoring of meat freshness by measuring the temperature, pH value or other indicators of meat and converting them into visual signals. This paper first summarizes the common types, basic principles and research progress of visual intelligent labels, then introduces its application in livestock, poultry and seafood freshness monitoring, finally looks forward to the development prospect of visual smart labels.

Recent Advances of Cellulose-Based Hydrogels Combined with Natural Colorants in Smart Food Packaging

Due to the frequent occurrence of food safety problems in recent years, healthy diets are gradually receiving worldwide attention. Chemical pigments are used in smart food packaging because of their bright colors and high visibility. However, due to shortcomings such as carcinogenicity, people are gradually looking for natural pigments to be applied in the field of smart food packaging. In traditional smart food packaging, the indicator and the packaging bag substrate have different degrees of toxicity. Smart food packaging that combines natural colorants and cellulose-based hydrogels is becoming more and more popular with consumers for being natural, non-toxic, environmentally friendly, and renewable. This paper reviews the synthesis methods and characteristics of cellulose-based hydrogels, as well as the common types and characteristics of natural pigments, and discusses the application of natural colorants and cellulose-based hydrogels in food packaging, demonstrating their great potential in smart food packaging.

Physical and thermal improvement of bioplastics based on potato starch/agar composite functionalized with biogenic ZnO nanoparticles

This study investigated potato starch/agar-based bioplastics' structure, properties, and biodegradability by adding ZnO nanoparticles (NPs) biogenically synthesized using Coriandrum sativum extract. ZnO NPs presented crystalline structure, good optical properties, and a size of 6.75 ± 1.4 nm, which were added at various concentrations (419.66-104.23 ppm) in bioplastics and their presence was confirmed via EDS elemental analysis and X-ray fluorescence. The highest NPs concentration contributed to a smoother surface, while FTIR and Raman analyses suggested interactions between the NPs and functional groups of the biopolymeric matrix. ZnO NPs addition slightly reduced bioplastic transparency but significantly improved UV-A and UV-B blocking capacities. It also increased hydrophobicity, evidenced by a 22 % reduction in water absorption and a 55 % increase in contact angle. Thermogravimetric analysis (TGA) indicated that NPs raised the bioplastic's thermal stability. Mechanical property tests showed that ZnO NPs concentrations had negligible or negative effects probably due to the heterogeneous distribution of NPs, or the non-isotropic characteristic of the bioplastic. Finally, biodegradability assays in seawater and soil revealed over 43.5 % and 66 % degradation after 15 and 28 days, respectively. Therefore, biosynthesized ZnO NPs mainly enhanced the bioplastic's UV-blocking capacity, hydrophobicity, and thermal properties, offering an eco-friendly option for future studies/applications.

The latest research progress on polysaccharides-based biosensors for food packaging: A review

In recent years, polysaccharide-based biosensors have emerged as promising technologies for intelligent food packaging, offering innovative solutions to enhance food quality and safety. This review highlights advancements in designing, developing, and applying these biosensors, particularly those utilizing polysaccharides such as chitosan, cellulose and alginate. Engineered with nanomaterials like ZnO, silver, and carbon nano-tubes demonstrated high sensitivity in real-time monitoring of food spoilage indicators, including pH changes, volatile nitrogen compounds and microbial activity. We discuss the electrochemical properties of these biosensors, highlighting how the integration of electrochemical methods significantly improves their detection capabilities within packaging environments, leading to sensor sensitivity enhancement, greater accuracy, and spoilage detection, ultimately extending the shelf life of perishable food products. Additionally, the review addresses the practical challenges of industrial implementation and explores future research directions for optimizing sensor functionality and scalability. The findings underscore the potential of polysaccharide-based intelligent packaging as a sustainable and effective alternative to conventional methods, paving the way for broader commercial adoption.

Development and investigation of a polysaccharide ternary nanocomposite based on basil seed gum/graphene oxide/anthocyanin for intelligent food packaging

A new pH-sensitive intelligent packaging system was developed composed of extracted and purified basil seed gum (BG) containing aqueous malva sylvestris extract (MS) and varying amounts of synthesized graphene oxide (GO). In the following, the characteristics of prepared films including spectroscopic, physio-mechanical, thermogravimetry, fracture-surface morphology, anthocyanin release, and pH and TVB-N sensitivity, were investigated. Our results revealed that the addition of 0.5 wt % MS into the BG matrix induced pH sensitivity to the film and resulted in a visible color change from pH 2.0 to 14.0; however, it reduced the thermal and physio-mechanical properties. In this regard, the effective presence of the optimum concentration of GO (0.25 wt%) in enhancing the mechanical and thermal properties of the BG-MS films was shown. Moreover, inspecting the release kinetics demonstrated a controllable release for BG-MS-GO film compared to the BG-MS film in 48 h. Furthermore, the total volatile basic nitrogen (TVB-N) content and pH value were shown to be highly correlated with the color changes of the freshness indicator film during the storage of salmon fillets at 25 °C for 36 h. Therefore, it was shown that BG-MS-GO film can be used as a highly effective freshness/spoilage indicator of proteinic products.

In situ growth of curcumin-loaded cellulose composite film for real-time monitoring of food freshness in smart packaging

Visual pH-responsive packaging material is particularly important in food supply chain safety monitoring due to their non-destructive monitoring method and intuitive result. However, it has always been limited by the instability performance of pH-response components and carriers, which further hinders its wide food safety application. To address these challenges, we selected cellulose with remarkable biocompatibility and mechanical properties as the carrier, and high pH-responsive curcumin to develop a smart packaging material (RC/GC composite film) with real-time food safety monitoring. Compared with pure cellulose film, the RC/GC composite film exhibited excellent mechanical properties (4-fold enhancement) and thermal stability (100 °C increasing). Meanwhile, based on the first reported strategy of curcumin in-situ growth during cellulose film formation, the RC/GC composite film exhibited exceptional antioxidant activity (89.2 %), antimicrobial property (91.6 %), and significant pH-responsive sensitivity (within 15 s). This innovative approach offers a new strategy for easy-to-use and effective monitoring of food spoilage in packaging materials.

Recent Advances in Purple Sweet Potato Anthocyanins: Extraction, Isolation, Functional Properties and Applications in Biopolymer-Based Smart Packaging

Petroleum-based plastic packaging materials have negative impacts on the environment and food safety. Natural biopolymer-based food packaging materials are the proper substitutes for plastic-based ones, which is because biopolymers are nontoxic, biodegradable and even edible. The incorporation of bioactive and functional substances into a biopolymer-based film matrix can produce novel smart packaging materials. Anthocyanins, one class of natural colorants with potent antioxidant activity and pH-response color-changing ability, are suitable for producing biopolymer-based smart packaging films. The purple sweet potato is a functional food rich in anthocyanins. In the past decade, numerous studies have reported the extraction of anthocyanins from purple sweet potato and the utilization of purple sweet potato anthocyanins (PSPAs) in biopolymer-based smart packaging film production. However, no specific review has summarized the recent advances on biopolymer-based smart packaging films containing PSPAs. Therefore, in this review, we aim to systematically summarize the progress on the extraction, isolation, characterization, purification and functional properties of PSPAs. Moreover, we thoroughly introduce the preparation methods, physical properties, antioxidant and antimicrobial activity, pH sensitivity, stability and applications of biopolymer-based smart packaging films containing PSPAs. Factors affecting the extraction and functional properties of PSPAs as well as the properties of biopolymer-based films containing PSPAs are discussed.

Intelligent Packaging Systems with Anthocyanin: Influence of Different Polymers and Storage Conditions

With the aim of meeting the growing demand for safe food, intelligent packaging has emerged, which monitors the conditions of the food and informs the consumer about its quality directly at the time of purchase. Among intelligent packaging options, colorimetric indicator films, which change color in response to changes in the food, such as the release of volatile compounds, have been widely studied. Among them, pH indicator films composed of dyes sensitive to small variations in the pH value of the food surface have received greater attention in recent years. Anthocyanins, which are natural pigments, have stood out as one of the most commonly used sources of dyes in the production of these indicator films. In this context, the present review aims to present an updated overview of research employing anthocyanins in indicator films, including their stability under different storage conditions, the influence of different polymers used in their production, and alternative techniques for maintaining stability.

Impact of environmental storage conditions on properties and stability of a smart bilayer film

This study aimed to investigate the behavior of smart bilayer films under various temperature and relative humidity (RH). Smart bilayer films were fabricated using sodium alginate with incorporated butterfly pea anthocyanin and agar containing catechin-lysozyme. Cellulose nanospheres were added at concentrations of 0% and 10% w/w of the film and subjected to test at 4 °C and 25 °C, considering different RHs (0%, 50%, and 80%). The results showed that RH had a greater impact on the mechanical properties than temperature, leading to a decrease in tensile strength and an increase in elongation at break with higher RH. The films displayed increased strength but reduced flexibility at low temperatures. Oxygen permeability was negatively affected by increasing RH, while water vapor barrier properties were better at 25 °C than at 4 °C. In terms of color stability, the temperature played a more important role, with both types of smart bilayer films retaining their color stability throughout 14-day storage at 4 °C, even maintaining their ability to change color with pH. However, the films stored at 25 °C exhibited lower color stability and showed potential for color change with varying pH levels, but with lower intensity. The findings of this study demonstrate the significant impact of temperature and RH on the functional properties of smart bilayer films, with and without the addition of cellulose nanospheres. Such smart bilayer films have great potential for various applications, particularly in food packaging, where maintaining color, mechanical, and barrier properties under varying environmental conditions is crucial.

Gellan gum and pullulan-based films with triple functionalities of antioxidant, antibacterial and freshness indication properties for food packaging

The objective of this research was to fabricate pH-responsive and active films based on gellan gum (GG) and pullulan (PL) with extracts of Broussonetia papyrifera fruits (BPFE) and leaves (BPLE) by a casting method. Results indicated that the extracts had good compatibility with GG and PL, which were uniformly distributed throughout the matrix. The incorporation of BPFE and BPLE increased the thickness, UV-vis barrier property, mechanical strength, thermal stability and moisture content of the films, while decreasing the water contact angle. Notably, the films exhibited enhanced antioxidant properties, with maximum radical scavenging rates of 77.45 % using 2,2 Diphenyl-1-picrylhydrazyl and 66.21 % using 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid). The antibacterial capability of the films also increased significantly after adding BPLE and BPFE. The results of XRD and FTIR showed that BPFE was bound to GG and PL by hydrogen bond. The release behavior of BPFE from the films agreed best with the first-level kinetic model. Furthermore, the films displayed obvious color responses to ammonia gas and different pH environments. Simultaneously, the films were applied to monitor the freshness of Pelteobagrus fulvidraco fish. The color parameters of the films demonstrated high correlations with the freshness indexes measured through standard laboratory procedures.

Digitalization of Colorimetric Sensor Technologies for Food Safety

Colorimetric sensors play a crucial role in promoting on-site testing, enabling the detection and/or quantification of various analytes based on changes in color. These sensors offer several advantages, such as simplicity, cost-effectiveness, and visual readouts, making them suitable for a wide range of applications, including food safety and monitoring. A critical component in portable colorimetric sensors involves their integration with color models for effective analysis and interpretation of output signals. The most commonly used models include CIELAB (Commission Internationale de l'Eclairage), RGB (Red, Green, Blue), and HSV (Hue, Saturation, Value). This review outlines the use of color models via digitalization in sensing applications within the food safety and monitoring field. Additionally, challenges, future directions, and considerations are discussed, highlighting a significant gap in integrating a comparative analysis toward determining the color model that results in the highest sensor performance. The aim of this review is to underline the potential of this integration in mitigating the global impact of food spoilage and contamination on health and the economy, proposing a multidisciplinary approach to harness the full capabilities of colorimetric sensors in ensuring food safety.

Blueberry anthocyanin based active intelligent wheat gluten protein films: Preparation, characterization, and applications for shrimp freshness monitoring

The aim of this study was to prepare active intelligent gluten protein films using wheat gluten protein (WG) and apple pectin (AP) as film-forming matrices, and blueberry anthocyanin extract (BAE) as a natural indicator. SEM and FT-IR analyses demonstrated the successful immobilization of BAE in the film matrix by hydrogen bonding interactions and its compatibility with WG and AP. The resultant WG-AP/BAE indicator films demonstrated notable antioxidant activity, color stability, barrier qualities, pH and ammonia response sensitivity, and mechanical properties. Among them, WG-AP/BAE5 exhibited the best mechanical properties (TS: 0.83 MPa and EB: 242.23%) as well as the lowest WVP (3.92 × 10-8 g.m/m2.Pa.s), and displayed high sensitivity to volatile ammonia. In addition, WG-AP/BAE5 showed a color shift from purplish red to green to yellowish green, demonstrating the monitoring of shrimp freshness in real time. Consequently, this study offers a firm scientific foundation for the development of active intelligent gluten protein films and their use in food freshness assessments.

Locust Bean Gum/κ-Carrageenan Film Containing Blueberry or Beetroot Extracts as Intelligent Films to Monitoring Hake (Merluccius merluccius) Freshness

The main goal of this work was to develop bio-based and ecofriendly intelligent films as freshness indicators to monitor European hake (Merluccius merluccius) quality during storage by using a visual, non-destructive, and real-time technique. Locust bean gum (LBG)/κ-carrageenan (Car) films incorporating blueberry extract (BLE) or beetroot extract (BEE) were developed and their effectiveness to detect hake deterioration during 7 days of storage at 4 °C was evaluated. A visible color response from pink to blue was observed on the BLE films at the end of hake storage, which correlated with the hake deterioration profile, namely an increase in pH values (from 6.60 ± 0.04 to 8.02 ± 0.03), total viable count (TVC, from 4.61 ± 0.36 to 8.61 ± 0.21 log CFU/g), and total volatile basic nitrogen content (TVB-N, from 10.21 ± 1.97 to 66.78 ± 4.81 mg/100 g) beyond the spoilage threshold. The results of this study are very promising, since it was possible to develop a new effective intelligent bio-based responsive indicator film incorporating natural dye BLE, which has the potential to contribute to food waste reduction and improve food safety by detecting the hake freshness status.

A review on the role of pH-sensitive natural pigments in biopolymers based intelligent food packaging films

As food packaging evolves, consumer interests are shifting from traditional to intelligent food packaging systems. Intelligent packaging includes active components that display changes in a visual or interactive form perceivable by consumers. This offers real-time monitoring of the quality and shelf life of the packaged food and enhances transparency. For example, pH-sensitive natural pigment-based films change color in response to variations in pH levels, enabling the film/labels to reflect alterations in the acidity or basicity of the food inside the package. Natural pigments like anthocyanins, curcumin, betalains, chlorophyll, and carotenoids have been comprehensively reported for developing biodegradable pH-sensitive films of starch, protein, chitosan, and cellulose. Natural pigments offer great compatibility with these biopolymers and improve the other performance parameters of the films. However, these films still lack the strength and versatility of petroleum-based synthetic plastic films. But these films can be used as an indicator and combined with primary packaging to monitor freshness, time-temperature, and leak for muscle foods, dairy products, fruits and vegetables, and bakery products. Therefore, this review provides a detailed overview of pH-sensitive pigments, their compatibility with natural polymers, their role in film performance in monitoring, and their food packaging applications.

Edible colorimetric label based on immobilized purple sweet potato anthocyanins onto edible film for packaged mushrooms freshness monitoring

An edible colorimetric label has been developed to determine the freshness level of mushrooms, i.e. white oyster mushrooms (Pleurotus ostreatus). The edible indicator label has been fabricated based on purple sweet potato (Ipomoea batatas L.) anthocyanins (PSPA) immobilized onto an edible film made of chitosan and cornstarch with added PVA. The freshness parameters of the mushrooms were pH, weight loss, texture, and sensory evaluation. The results showed that the colorimetric label was dark purple when the mushroom was fresh, and turn to light purple when the mushroom was still fresh, and finally green when the mushroom was no longer fresh. The color value (mean Red) of the label was measured using the ImageJ program, where its color value (mean Red) increased with decreasing freshness level of the mushrooms. The edible label can distinguish fresh mushrooms from spoilage, making it suitable to be used in a packaged mushroom as a freshness indicator.

A comparative study on the structure, physical property and halochromic ability of shrimp freshness indicators produced from nine varieties of steamed purple sweet potato

Nine varieties of purple sweet potato were steamed and used for the production of shrimp freshness indicators. The impact of purple sweet potato's variety on the structure, physical property and halochromic ability of indicators was determined. Results showed different varieties of purple sweet potato had different starch, crude fiber, pectin, protein, fat and total anthocyanin contents. The microstructure, crystallinity, moisture content, water vapor permeability, tensile strength and elongation at break of indicators were affected by crude fiber content in purple sweet potato. The color, transmission and halochromic ability of indicators was associated with the total anthocyanin content in purple sweet potato. Freshness indicators produced from Fuzi No. 1, Ganzi No. 6, Ningzi No. 2, Ningzi No. 4, Qining No. 2 and Qining No. 18 of purple sweet potato were suitable to indicate shrimp freshness. This study provides useful information on screening suitable varieties of purple sweet potato for intelligent packaging.

Active and smart biomass film with curcumin Pickering emulsion stabilized by chitosan-adsorbed laurate esterified starch for meat freshness monitoring

The multifunctional active smart biomass film was prepared by incorporating chitosan-adsorbed laurate esterified starch curcumin Pickering emulsion into the starch film matrix, with nano-cellulose serving as reinforcing agents. The mechanical and functional properties of the film were studied, and the film was used to monitor the freshness of pork. The results demonstrated a relatively uniform distribution of curcumin and Pickering emulsion droplets within the film matrix. Furthermore, the thermal stability was minimally impacted by the introduction of curcumin Pickering emulsion, while the tensile strength and tensile strain of the film were increased, and both its hydrophobicity and antioxidant properties were improved. The free radical scavenging rate reached 56.01 %, with sustained high antioxidant capacity even after 8 days. Additionally, the presence of curcumin provided the film with pH indicating ability and delayed pork spoilage. Therefore, this work provides an attractive strategy for constructing green, active, and smart biomass packaging films for meat packaging applications.

Plant betalains-mixed active/intelligent films for meat freshness monitoring: A review of the fabrication parameters

The plant pigments called betalains are nutritionally safe polar compounds. They are subdivided into betaxanthins (having orange to yellow hues) and betacyanins (purple to red violet hues). Betacyanins change color with a change in pH, particularly in the range 6-8 and 9-11. Perishable foods like fish, chicken, beef, pork, and others tend to release total volatile base-nitrogen (TVB-N) during storage or deterioration, which leads to a change in the pH of pH-sensitive materials in the vicinity. pH-sensitive pigment-incorporated polymeric films with inherent active properties (or active/intelligent films) are increasingly being studied as an alternative to synthetic pH indicators to detect the accumulation of TVB-N by changing its color to indicate the stage of perishable food spoilage. There are many methods of developing such films under different conditions using different bio-based biodegradable polymer(s) and biocompatible plasticizer combinations. Among the reported methods, solution casting method has been the preferred one in most studies covered in this review. This method can be carried out under mild conditions. As such, betacyanins-incorporated polymeric films essentially require mild processing conditions because of their heat sensitivity, which will invariably affect the performance in food freshness monitoring. In this review, film fabrication parameters like temperature and duration of dissolution of polymers, plasticizer concentration, pH of the film-forming solution, film drying, and conditioning/aging, have been critically appraised based on the available literature. The lack of studies on the safety of active/intelligent films has been systematically highlighted in this review to focus future studies on this area.

Graphical abstract

Smart colorimetric indicator films prepared from chitosan and polyvinyl alcohol with high mechanical strength and hydrophobic properties for monitoring shrimp freshness

This work aimed to develop and characterize a colorimetric indicator films based on chitosan (CS), polyvinyl alcohol (PVA), and shikonin (SKN) from radix Lithospermi by casting method. The prepared films can serve as smart packaging for monitoring shrimp freshness which having excellent antimicrobial and antioxidant activity. The shikonin containing films have better hydrophobicity, barrier properties, and tensile strength. The release kinetics analysis shows that the loading amount causes a prolonged release of SKN from the prepared films. Increasing SKN in the CS/PVA film from 1 wt% to 2 wt% improved antibacterial effect for 24 h. Additionally, pH-sensitive color shifts from reddish (pH 2) to purple-bluish (pH 13) were visually seen in shikonin based solutions as well as films. The CS/PVA/SKN film detected shrimp deterioration at three temperatures (25, -20, and 4 °C) through color change. This study introduces a favorable approach for smart packaging in the food industry using multifunctional films.

Nelumbo nucifera flower extract incorporated alginate/polyvinyl alcohol films as a sustainable pH indicator for active food packaging applications

In recent years, there has been a growing demand for environmentally friendly smart packaging materials. Therefore, in this study, we developed an eco-friendly pH-sensitive indicator film through the solvent casting process, incorporating alginate, polyvinyl alcohol, garlic, and Nelumbo nucifera flower extract. The effect of extract on the chemical and physical properties of the film were extensively studied using various characterization techniques. XRD and FTIR reveal the strong interaction between the polymers and the extract. The incorporation of the extract influenced various parameters such as swelling behavior, water solubility, and moisture content, while also improving the film's thermal stability, biodegradability, as well as its antioxidant and antimicrobial properties. Interestingly, the film exhibited a color change in response to pH change. During shrimp storage, the film showed a visible transition from purple to green, indicating shrimp spoilage. Additionally, the film's ability to detect freshness was confirmed by measuring total volatile basic nitrogen (TVBN). These findings suggest that the PVA/alginate/garlic/Nelumbo nucifera film shows promise as an intelligent packaging material for real-time food monitoring applications.

Development of an UV-Resistant Multilayer Film with Enhanced Compatibility between Carboxymethyl Cellulose and Polylactic Acid via Incorporation of Tannin and Ferric Chloride

Carboxymethyl cellulose (CMC) and polylactic acid (PLA) are recognized for their environmental friendliness. By merging them into a composite film, packaging solutions can be designed with good performance. Nonetheless, the inherent interface disparity between CMC and PLA poses a challenge, and there may be layer separation issues. This study introduces a straightforward approach to mitigate this challenge by incorporating tannin acid and ferric chloride in the fabrication of the CMC-PLA. The interlayer compatibility was improved by the in situ formation of a cohesive interface. The resulting CMC/TA-PLA/Fe multilayer film, devoid of any layer separation, exhibits exceptional mechanical strength, with a tensile strength exceeding 70 MPa, a high contact angle of 105°, and superior thermal stability. Furthermore, the CMC/TA-PLA/Fe film demonstrates remarkable efficacy in blocking ultraviolet light, effectively minimizing the discoloration of various wood surfaces exposed to UV aging.

Fabrication and characterization of sodium alginate/blueberry anthocyanins/hinokitiol loaded ZIF-8 nanoparticles composite films with antibacterial activity for monitoring pork freshness

A smart film was developed to detect the freshness of pork by incorporating blueberry anthocyanins (BAs) and hinokitiol (HIN) loaded zeolite-imidazolium framework (HIN@ZIF-8) with into a sodium alginate matrix, and its microstructure and physicochemical properties were studied. The SA matrix was doped with BAs and HIN@ZIF-8 nanoparticles (SA-BAs/HIN@ZIF-8) to increase its tensile strength and reduce its water vapor permeability. HIN@ZIF-8 has low cytotoxicity, and SA-BAs/HIN@ZIF-8 membranes have long-lasting antimicrobial and highly sensitive color development properties against Escherichia coli and Staphylococcus aureus. The results of pork preservation experiments showed that SA-BA/HIN@ZIF-8 could extend the shelf life of pork to 6 days at 4 ℃. E-nose evaluation experiments showed that SA-BAs/HIN@ZIF-8 could inhibit compounds that cause unpleasant and irritating odours. Therefore, SA-BAs/HIN@ZIF-8 was considered to be an effective method to improve the freshness of pork, and the results showed that it has a promising application in food preservation.

Natural colorant incorporated biopolymers-based pH-sensing films for indicating the food product quality and safety

The current synthetic plastic-based packaging creates environmental hazards that impact climate change. Hence, the topic of the current research in food packaging is biodegradable packaging and its development. In addition, new smart packaging solutions are being developed to monitor the quality of packaged foods, with dual functions as food preservation and quality indicators. In the creation of intelligent and active food packaging, many natural colorants have been employed effectively as pH indicators and active substances, respectively. This review provides an overview of biodegradable polymers and natural colorants that are being extensively studied for pH-indicating packaging. A comprehensive discussion has been provided on the current status of the development of intelligent packaging systems for food, different incorporation techniques, and technical challenges in the development of such green packaging. Finally, the food industry and environmental protection might be revolutionized by pH-sensing biodegradable packaging enabling real-time detection of food product quality and safety.

Enhanced antioxidant and antibacterial activities of chitosan/zein nanoparticle Pickering emulsion-incorporated chitosan coatings in the presence of cinnamaldehyde and tea polyphenol

Pickering emulsions were prepared by using zein/chitosan nanoparticles as stabilizer and then incorporated into chitosan coatings. To improve the stability and performances, tea polyphenol and cinnamaldehyde (CA) were used to modulate the formation and functionalities of Pickering emulsions. The oil phase in Pickering emulsions were set at 5 % and 20 % to alter the hydrophobicity of chitosan coatings. Physical, structural, antioxidant and antibacterial activities of chitosan coatings with Pickering emulsions were characterized. Tea polyphenol significantly enhanced antioxidant capacity of chitosan coatings from 2.09 % to 57.61 % of DPPH value and from 2.63 % to 38.85 % of ABTS value. CA effectively increased the antibacterial activity of chitosan coatings against S. aureus and E. coli. Under 20 % oil content, the inhibition zones on S. aureus and E. coli increased from 3.03 ± 0.23 mm to 18.39 ± 1.22 mm and 7.66 ± 1.61 mm to 15.70 ± 1.75 mm, respectively. The preservative effect of chitosan coatings on fresh pork was further confirmed that the shelf-life of fresh pork could be extended by >4 days. These results suggested a great potential application of Pickering emulsion-incorporated chitosan coatings in the preservation of fresh pork.

Edible film preparation by anthocyanin extract addition into acetylated cassava starch/sodium carboxymethyl cellulose matrix for oxidation inhibition of pumpkin seeds

In this study, an edible film was fabricated by incorporating anthocyanin extract from black rice (AEBR) into acetylated cassava starch (ACS)/carboxymethyl-cellulose (CMC) to enhance the shelf life of pumpkin seeds. The effects of AEBR on the rheological properties of film-forming solutions, as well as the structural characterization and physicochemical properties of the film, were evaluated. Rheological properties of solutions revealed that AEBR was evenly dispersed into polymer matrix and bound by hydrogen bonds, as confirmed by Fourier transform infrared spectroscopy analysis. The appropriate AEBR addition could be compatible with polymer matrix and formed a compact film structure, improving the mechanical properties, barrier properties, and opacity. However, with further addition of AEBR, the tensile strength and water vapor permeability decreased and the tight structure was destroyed. After being stored separately under thermal and UV light accelerated conditions for 20 days, the peroxide value and acid value of roasted pumpkin seeds coated with the AEBR film showed a significant reduction. Moreover, the storage stability of AEBR was improved through the embedding of ACS/CMC biopolymers. These results indicated that AEBR film could effectively delay pumpkin seeds oxidation and prolong their shelf life as an antioxidant material.

Development of a pH-responsive intelligent label using low molecular weight chitosan grafted with phenol red for food packaging applications

In this study, we successfully developed a screen-printed pH-responsive intelligent label using low molecular weight chitosan grafted with phenol red (LCPR) as a colorant for screen printing ink. The LCPR was synthesized via a Mannich reaction, and its successful grafting was confirmed through FT-IR, UV-vis, and NMR spectroscopy. The LCPR exhibited lower crystallinity and thermal stability compared to low molecular weight chitosan (LC) and demonstrated zwitterionic behavior. To create intelligent labels, the LCPR-based ink was efficiently printed on cotton substrates with high resolution. The label exhibited remarkable sensitivity to buffer pH solutions and ammonia gas, leading to distinctive color changes from orange to red to purple. Additionally, the label showed excellent reversibility, storage stability, and leaching resistance to different food simulant solutions. The label was utilized to monitor shrimp freshness, successfully detecting a noticeable color shift upon spoilage. These findings highlight the significant potential of the LCPR-based label as an intelligent food packaging solution, offering pH-responsiveness and color stability for qualitative freshness detection of protein-rich food.

Eggshell membrane as a novel and green platform for the preparation of highly efficient and reversible curcumin-based colorimetric sensor for the monitoring of chicken freshness

Herein, for the very first time, we report a paper-like biomass, eggshell membrane (ESM), as a suitable platform for the fabrication of a colorimetric sensor (E-Cot). Green ethanolic extract, curcumin (CUR), was used as a sensing material to coat with the ESM. The present E-Cot effectively changed its color (yellow to red) in the real-time monitoring for chicken spoilage. The E-Cot exhibits barrier properties due to its inherent semi-permeability characteristics. Interestingly, the E-Cot showed a significant change in total color difference value (ΔE, 0 days - 0.0-39.6, after 1 day - 39.6-42.1, after 2 days - 42.1-53.6, after 3 days- 53.6-60.1, and after 4 days - 60.1-66.3, detectable by the naked eye) in the real-time monitoring for chicken freshness. In addition, the present E-Cot smart colorimetric sensor is reversible with a change in pH, and the sensor can be reused. Further, the hydrophobic nature of the E-Cot was confirmed by water contact angle analysis (WCA, contact angle of 101.21 ± 8.39). Good antibacterial, barrier, and optical properties of the present E-Cot were also found. Owing to the advantages such as green, efficient, cost-effective, biodegradable, reusable, sustainable, and simple preparation, we believe that the present E-Cot would be a more attractive candidate.

Fabrication of multifunctional ethyl cellulose/gelatin-based composite nanofilm for the pork preservation and freshness monitoring

In this study, an active and intelligent nanofilm for monitoring and maintaining the freshness of pork was developed using ethyl cellulose/gelatin matrix through electrospinning, with the addition of natural purple sweet potato anthocyanin. The nanofilm exhibited discernible color variations in response to pH changes, and it demonstrated a higher sensitivity towards volatile ammonia compared with casting film. Notably, the experimental findings regarding the wettability and pH response performance indicated that the water contact angle between 70° and 85° was more favorable for the smart response of pH sensitivity. Furthermore, the film exhibited desirable antioxidant activities, water vapor barrier properties and also good antimicrobial activities with the incorporation of ε-polylysine, suggesting the potential as a food packaging film. Furthermore, the application preservation outcomes revealed that the pork packed with the nanofilm can prolong shelf life to 6 days, more importantly, a distinct color change aligned closely with the points indicating the deterioration of the pork was observed, changing from light pink (indicating freshness) to light brown (indicating secondary freshness) and then to brownish green (indicating spoilage). Hence, the application of this multifunctional film in intelligent packaging holds great potential for both real-time indication and efficient preservation of the freshness of animal-derived food items.

Active cellulose acetate/purple sweet potato anthocyanins@cyclodextrin metal-organic framework/eugenol colorimetric film for pork preservation

As a natural pH-sensing colorant, purple sweet potato anthocyanins (PSPAs) have demonstrated great potential in colorimetric film for freshness monitoring. However, the photothermal instability of PSPAs is still a challengeable issue. Herein, γ-cyclodextrin metal-organic framework (CD-MOF) loaded with PSPAs (PSPAs@CD-MOF, i.e., PM) and eugenol (EUG) were incorporated in cellulose acetate (CA) matrix for developing a smart active colorimetric film of CA/PM/EUG, where PM and EUG were hydrogen-bonded with CA. Attentions were focused on the photothermal colorimetric stability, colorimetric response, and antibacterial activity of the films. The presence of PM and EUG endowed the film outstanding UV-blocking performance and enhanced the barrier against water vapor and oxygen. Target film of CA/PM15/EUG10 had good photothermal colorimetric stability due to the protection of CD-MOF on PSPAs and the color changes with pH-stimuli were sensitive and reversible. In addition to antioxidant activity, CA/PM15/EUG10 had antibacterial activity against Escherichia coli and Staphylococcus aureus. The application trial results indicated that the CA/PM15/EUG10 was valid to indicate pork freshness and extended the shelf-life by 100 % at 25 °C, which has demonstrated a good perspective on smart active packaging for freshness monitoring and shelf-life extension.

Smart labels based on polyvinyl alcohol incorporated with chitosan nanoparticles loaded with grape extract: Functionality, stability and food application

Anthocyanins (ACNs) are natural compounds with potential applications due to their colorimetric response to pH. Due to their sensitivity to various environmental factors, nanoencapsulation with biopolymers is a successful strategy for stabilizing ACNs. In this work ACNs were extracted from grape skins and encapsulated into chitosan (CS) nanoparticles by ionic gelation using sodium tripolyphosphate (TPP) as a cross-linking agent. CS nanoparticles loaded with ACNs had particle sizes between 291 and 324 nm and polydispersity index around 0.3. The encapsulation efficiency of ACNs was approximately 60 %; and encapsulated anthocyanins (ACN-NPs) exhibited color change properties under different pH conditions. pH-sensitive labels based on polyvinyl alcohol (PVA) were prepared by the casting method. The effect of incorporating ACN-NPs on the physical, structural, and pH-sensitive properties of PVA labels was evaluated, and its application as shrimp freshness indicator was studied. The nanoencapsulation protected ACNs against heat and light treatments, preserving the original purple color. When applying the label, visible changes from red to blue until reaching yellow were observed with the change in the quality of the shrimp at the refrigeration temperature. The results suggest that PVA labels containing ACNs encapsulated in C-NPs can be used as smart packaging labels in the food industry.

Aerogel colorimetric label sensors based on carboxymethyl cellulose/sodium alginate with black goji anthocyanin for monitoring fish freshness

A novel colorimetric aerogel was developed by the complexation of carboxymethyl cellulose (CMC), sodium alginate (SA), and black goji anthocyanin (BGA) followed by freeze-drying for monitoring fish (Coho salmon) freshness during storage at 4 °C and 25 °C. The various aerogels (C/S/B3:1, C/S/B2:1, C/S/B1:1, C/S/B1:2, and C/S/B1:3) externally and internally were characterized using SEM, FTIR, XRD, DSC, and TGA. Among them, the aerogel composite C/S/B1:2 exhibited the most uniform pore size, largest specific surface area, rapid color changes in various alkaline vapors (5 μM and 50 μM), and better mechanical strength. Furthermore, the colorimetric aerogel became dark blue from light purple during fish storage at temperatures of 4 °C and 25 °C when it reached pH 7.49 and 7.33, TVC 8.9 × 107 CFU/g and 8.5 × 107 CFU/g, and TVB-N 33.8 mg/100 g and 26.12 mg/100 g, respectively, indicating fish completely deteriorated. Taken together, the colorimetric aerogel composite C/S/B1:2 was promising for determining fish freshness, which could be utilized as a non-destructive and useful intelligent sensor in monitoring various fish and meat freshness and/or quality.

Time-temperature indicator of hydroxyethyl cellulose ink labels for assessing pork freshness

Pork is widely consumed worldwide, and many consumers now utilize sensory evaluation techniques to determine the freshness of pork when buying it. A color-changing ink label utilizing bromocresol purple (BCP) and N-hydroxyphthalimide (NHPI) had been created to help consumers better and more rapidly determine the freshness of pork while it is stored. The ink was easy to prepare and could be readily transferred to A4 paper using screen printing technology. This study delved deeper into the impact of hydroxyethyl cellulose (HEC) on the functional properties of inks to enhance printing performance. The experiment demonstrated that a 1 % mass fraction of HEC improved thixotropy and facilitated the even distribution of ink on A4 paper, as confirmed by scanning electron microscopy. Screen-printed labels with varying concentrations displayed distinct color change rates when stored at different temperatures, indicating their capability to assess pork freshness. FT-IR, laboratory, and stability tests verified the ink's exceptional color change capabilities and printing attributes. An analysis using the Arrhenius equation revealed a substantial synergistic effect between BCP and NHPI, resulting in improved sensitivity and accuracy of the ink. This study offers a practical and feasible method to monitor the storage quality of pork effectively.

Recent advances in modified starch based biodegradable food packaging: A review

This study reviews the importance of resistant starch (RS) as the polymer of choice for biodegradable food packaging and highlights the RS types and modification methods for developing RS from native starch (NS). NS is used in packaging because of its vast availability, low cost and film forming capacity. However, application of starch is restricted due to its high moisture sensitivity and hydrophilic nature. The modification of NS into RS improves the film forming characteristics and extends the applications of starch into the formulation of packaging. The starch is blended with other bio-based polymers such as guar, konjac glucomannan, carrageenan, chitosan, xanthan gum and gelatin as well as active ingredients such as nanoparticles (NPs), plant extracts and essential oils to develop hybrid biodegradable packaging with reduced water vapor permeability (WVP), low gas transmission, enhanced antimicrobial activity and mechanical properties. Hybrid RS based active packaging is well known for its better film forming properties, crystalline structures, enhanced tensile strength, water resistance and thermal properties. This review concludes that RS, due to its better film forming ability and stability, can be utilized as polymer of choice in the formulation of biodegradable packaging.

Highly sensitive fiber-optic chemical pH sensor based on surface modification of optical fiber with ZnCdSe/ZnS quantum dots

The pH value plays a vital role in many biological and chemical reactions. In this work, the fiber-optic chemical pH sensors were fabricated based on carboxyl ZnCdSe/ZnS quantum dots (QDs) and tapered optical fiber. The photoluminescence (PL) intensity of QDs is pH-dependence because protonation and deprotonation can affect the process of electron-hole recombination. The evanescent wave of tapered optical fiber was used as excitation source in the process of PL. To obtain higher sensitivity, the end faces of fiber were optimized for cone region. By lengthening the cone region and shrinking the end diameter of optical fiber, evanescent wave was enhanced and the excitation times of QDs were increased, which improved the PL intensity and the sensitivity of the sensor. The sensitivity of sensor can reach as high as 0.139/pH in the range of pH 6.00-9.01. The surface functional modification was adopted to prepare sensing films. The carboxyl groups on the QDs ligands are chemically bonded to the fiber surface, which is good for response time (40 s) and stability (decreased 0.9 % for 5 min). These results demonstrated that ZnCdSe/ZnS QDs-based fiber-optic chemical pH sensors are promising approach in rapid and precise pH detection.

Anti-bacterial films developed by incorporating shikonin extracted from radix lithospermi and nano-ZnO into chitosan/polyvinyl alcohol for visual monitoring of shrimp freshness

In recent years, the utilization of smart colorimetric packaging films for monitoring food freshness has garnered significant concentration. However, their limited tensile strength, hydrophobicity, antioxidant, and antibacterial properties have been substantial barriers to widespread adoption. In this study, we harnessed the potential of biodegradable materials, specifically chitosan/polyvinyl alcohol, alongside shikonin extracted from Radix Lithospermi and ZnO nanoparticles, to create a novel colorimetric sensing film. This film boasts an impressive tensile strength of 82.36 ± 2.13 MPa, enhanced hydrophobic characteristics (exemplified by a final contact angle of 99.81°), and outstanding antioxidant and antibacterial properties. It is designed for real-time monitoring of shrimp freshness. Additionally, we verified the effectiveness of this sensing film in detecting shrimp freshness across varying temperature conditions, namely 25 °C and 4 °C was validated through the measurement of total volatile basic nitrogen (TVB-N). Visual inspection unequivocally revealed a transition in color from dark red to purple-light blue and finally to dark bluish providing a clear indication of shrimp spoilage, which demonstrated a strong correlation with the TVB-N content in shrimp measured through standard laboratory procedures. The colorimetric sensing film developed in this study holds great promise for creating smart labels with exceptional antioxidant and antibacterial properties, tailored for visual freshness monitoring of shrimp.