Preparation and characterization of a poly(ether-block-amide) film–based CO2 indicator for monitoring kimchi quality

Application of nano-ZnO in the food preservation industry: antibacterial mechanisms, influencing factors, intelligent packaging, preservation film and safety

In recent years, how to improve the functional performance of food packaging materials has received increasing attention. One common inorganic material, nanometer zinc oxide (ZnO-NPs), has garnered significant attention due to its excellent antibacterial properties and sensitivity. Consequently, ZnO-NP-based functional packaging materials are rapidly developing in the food industry. However, there is currently a lack of comprehensive and systematic reviews on the use of ZnO-NPs as functional fillers in food packaging. In this review, we introduced the characteristics and antibacterial mechanism of ZnO-NPs, and paid attention to the factors affecting the antibacterial activity of ZnO-NPs. Furthermore, we systematically analyzed the application of intelligent packaging and antibacterial packaging containing ZnO-NPs in the food industry. At the same time, this paper also thoroughly investigated the impact of ZnO-NPs on various properties including thickness, moisture resistance, water vapor barrier, mechanical properties, optical properties, thermal properties and microstructure of food packaging materials. Finally, we discussed the migration and safety of ZnO-NPs in packaging materials. ZnO-NPs are safe and have negligible migration rates, simultaneously their sensitivity and antibacterial properties can be used to detect the quality changes of food during storage and extend its shelf life.

Ammonia/pH super-sensitive colorimetric labels based on gellan gum, sodium carboxymethyl cellulose, and dyes for monitoring freshness of lamb meat

This study aimed to develop an ammonia and pH super-sensitive label by incorporating methyl red and bromothymol blue (MR-BTB, MB) into gellan gum/sodium carboxymethyl cellulose (GG/CMC-Na, GC). Furthermore, E-nose as an auxiliary tool combined with the labels to monitor meat freshness. Results showed that MB had more color change than pure MR or BTB, and the detection limit of ammonia about the MR-BTB (1:2) group was only 2.82 ppm. The addition of MB significantly increased tensile strength, moisture content, and water solubility, but decreased elongation at break and transmittance of the GC label (p < 0.05). The result of FTIR and SEM indicated the formation of hydrogen bonds and well compatibility between MB and GC. Furthermore, the color of the GC-10.0MB label was constantly obviously changing during meat storage, indicating that the GC-10.0MB label had great potential for monitoring the freshness of the lamb meat. A high correlation was found between ΔE of GC-10.0MB label and TVB-N (R2 = 0.9092) and pH (R2 = 0.9114) of meat. Interestingly, the high correlation between ΔE of GC-10.0 MB label and the response value of S2 (R2 = 0.7531), S6 (R2 = 0.9921), and S7 sensor (R2 = 0.8325) of E-nose was also found.

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.

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.

Development of real time-pH sensitive intelligent indicators for monitoring chicken breast freshness/spoilage using real packaging practices

Real-real time CO2-sensitive freshness indicators, phenol red (PR) and bromothymol blue (BTB) dyes, in three-layer system using cellulose based binder was developed to determine the freshness/spoilage of chicken breast. The developed indicators were used to monitor chicken meat spoilage packaged in polyamide/polyethylene (PA/PE) pouches under air and 100% nitrogen (N2) at 4 °C for 10 days. Changes in the ΔE and ΔRGB values of the indicators, CO2/O2 gas composition of packs, and chemical (TVBN, pH, trimethylamine), microbial, and sensory quality parameters of chicken breast meat were analyzed. The visual color change in the PR-based indicator was insufficient for the consumer to detect the spoilage with the naked eye in both simulation and food trial. However, three stage color (dark blue-turquoise-green) change was occurred in BTB-based indicators, and the color transition in the spoilage level of CO2 (10-15% (v/v)) is supported by the physicochemical, microbiological and sensorial properties of the chicken breast. The shelf life of chicken breast under air was limited to 4 days, while the shelf life under 100% N2 was 6 days which are supported by the visual color change of BTB indicator. The BTB-based indicators were found promising on a real packaging conditions and could be adapted to industrial scale for monitoring real-time freshness/spoilage of poultry, ensuring food safety.

Development of Smart Films of a Chitosan Base and Robusta Coffee Peel Extract for Monitoring the Fermentation Process of Pickles

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.

Reflections on food security and smart packaging

Estimating the number of COVID-19 cases in 2020 exacerbated the food contamination and food supply issues. These problems make consumers more concerned about food and the need to access accurate information on food quality. One of the main methods for preserving the quality of food commodities for export, storage, and finished products is food packaging itself. In the food industry, food packaging has a significant role in the food supply which acts as a barrier against unwanted substances and preserves the quality of the food. Meanwhile, packaging waste can also harm the environment; namely, it can become waste in waterways or become garbage that accumulates because it is nonrenewable and nonbiodegradable. The problem of contaminated food caused by product packaging is also severe. Therefore, to overcome these challenges of safety, environmental impact, and sustainability, the role of food packaging becomes very important and urgent. In this review, the authors will discuss in more detail about new technologies applied in the food industry related to packaging issues to advance the utilization of Smart Packaging and Active Packaging.

Preparation of Methylcellulose Film-Based CO2 Indicator for Monitoring the Ripeness Quality of Mango Fruit cv. Nam Dok Mai Si Thong

Day-to-day advancements in food science and technology have increased. Indicators, especially biopolymer-incorporated organic dye indicators, are useful for monitoring the ripeness quality of agricultural fruit products. In this investigation, methylcellulose films—containing pH dye-based indicators that change color depending on the carbon dioxide (CO₂) levels—were prepared. The level of CO₂ on the inside of the packaging container indicated the ripeness of the fruit. Changes in the CO₂ level, caused by the ripeness metabolite during storage, altered the pH. The methylcellulose-based film contained pH-sensitive dyes (bromothymol blue and methyl red), which responded (through visible color change) to CO₂ levels produced by ripeness metabolites formed during respiration. The indicator solution and indicator label were monitored for their response to CO₂. In addition, a kinetic approach was used to correlate the response of the indicator label to the changes in mango ripeness. Color changes (the total color difference of a mixed pH dye-based indicator), correlated well with the CO₂ levels in mango fruit. In the ‘Nam Dok Mai Si Thong’ mango fruit model, the indicator response correlated with respiration patterns in real-time monitoring of ripeness at various constant temperatures. Based on the storage test, the indicator labels exhibited color changes from blue, through light bright green, to yellow, when exposed to CO₂ during storage time, confirming the minimal, half-ripe, and fully-ripe levels of mango fruit, respectively. The firmness and titratable acidity (TA) of the fruit decreased from 44.54 to 2.01 N, and 2.84 to 0.21%, respectively, whereas the soluble solid contents (SSC) increased from 10.70 to 18.26% when the fruit ripened. Overall, we believe that the application of prepared methylcellulose-based CO₂ indicator film can be helpful in monitoring the ripeness stage, or quality of, mango and other fruits, with the naked eye, in the food packaging system.

Properties and Applications of Intelligent Packaging Indicators for Food Spoilage

Food packaging plays a vital role in the food supply chain by acting as an additional layer to protect against food contamination, but the main function of traditional conventional packaging is only to isolate food from the outside environment, and cannot provide related information about food spoilage. Intelligent packaging can feel, inspect, and record external or internal changes in food products to provide further information about food quality. Importantly, intelligent packaging indicators will account for a significant proportion of the food industry’s production, with promising application potential. In this review, we mainly summarize and review the upcoming progress in the classification, preparation, and application of food packaging indicators. Equally, the feasibility of 3D printing in the preparation of intelligent food packaging indicators is also discussed in detail, as well as the limitations and future directions of smart food packaging. Taken together, the information supported in this paper provides new insights into monitoring food spoilage and food quality.

Recent advances in intelligent food packaging materials: Principles, preparation and applications

Traditionally, food packaging is used for improving food quality and providing consumers with descriptions of products. A new generation of intelligent ("smart") packaging materials is being developed to continuously monitor the properties of packaged foods and provide real-time information about their maturity, quality, and safety. In this paper, recent research in the development, properties, and applications of intelligent food packaging materials is summarized. Initially, we review the different sensing methods that can be used to detect alterations in food properties, such as those based on changes in time, temperature, humidity, oxygen levels, pH, chemical composition, or microbial contamination. The different approaches that can be used to design intelligent packaging materials are then highlighted, including films, bar codes, and labels. A number of applications of these packaging materials are then discussed to demonstrate their potential in the food industry. Finally, the challenges and future directions of food packaging are discussed.

Preparation of pH-indicator films based on soy protein isolate/bromothymol blue and methyl red for monitoring fresh-cut apple freshness

Intelligent pH-indicator films based on soy protein isolate (SPI) were prepared using pH-sensitive dyes (bromothymol blue and methyl red). The addition of mixed indicators imparts pH-indicator films with an appreciable microstructure, acceptable water resistance, and favorable optical properties. The incorporation of the mixed indicators did not lead to significant improvement in the mechanical properties of films due to weak ionic cross-linking by hydrogen bonding between the SPI macromolecules and low-molecular-weight indicators. Fourier-transform infrared spectroscopy indicated hydrogen bond-mediated intermolecular interactions, and scanning electron microscopy showed that BB/MR were well dispersed in the SPI film. The indicator addition hindered the sorption and passage of water molecules. The water vapor permeability, moisture sorption, moisture content, and total soluble matter were 4.32 to 6.12 ×10^-12  g·cm/cm² ·s·Pa, 36.70% to 73.33%, 25.28% to 44.11%, and 8.21% to 25.56%, respectively. Also, the addition of indicators reduced UV light transmittance with minimal effect on the transparency of the film. The presence of indicators enhanced the pH sensitivity, seen as a visible color reaction at different pHs (total color difference, ΔE > 5). When the pH-indicator film containing 8 ml/100 ml final film emulsions was used to monitor the fresh-cut apple freshness, a green color for fresh status was observed, which turned blue after 60 h. Collectively, our findings suggested that indicator-containing SPI films have the potential for monitoring the freshness of fruits. PRACTICAL APPLICATION: pH-indicator films can help consumers to identify the freshness of packaged food by a change in the color of the packaging material, which is easily visible to the unaided eye without the need for opening the packaging. This protects consumers' interests.

Segmented-Block Poly(ether amide)s Containing Flexible Polydisperse Polyethyleneoxide Sequences and Rigid Aromatic Amide Moieties

We describe the synthesis and characterization of three novel aromatic diamines containing oxyethylene sequences of different lengths. These diamines were polymerized using the low-temperature solution polycondensation method with isophthaloyl chloride (IPC), terepthaloyl chloride (TPC), [1,1'-biphenyl]-4,4'-dicarbonyl dichloride (BDC), and 4,4'-oxybis(benzoyl chloride) (OBE), obtaining twelve poly(ether amide)s with short segments of polydisperse polyethyleneoxide (PEO) sequences in the polymer backbone. These polymers show reasonably high molecular mass materials (Mw > 12,000), and the relationship between their structure and properties has been carefully studied. Compared with conventional polyamides containing monodisperse PEO sequences, the polydispersity of the PEO segments within the structural units exerts a significant influence on the crystallinity, flexibility, solubility, and the thermal properties of the polymers. For instance, the all-para oriented polyamides (TPCP-A), with an average number of 8.2 ethylenoxide units per structural unit can be transformed conventionally (T_m = 259 °C) in comparison with thermally untransformable polymer with 2 ethylenoxide units (T_m = 425 °C).

A critical review on intelligent and active packaging in the food industry: Research and development

The emergence of many new food products on the market with need of consumers to constantly monitor their quality until consuming, in addition to the necessity for reducing food corruption during preservation time, have led to the development of some modern packaging technologies such as intelligent packaging (IP) and active packaging (AP). The benefits of IP are detecting defects, quality monitoring and tracking the packaged food products to control the storage conditions from the production stage to the consumption stage by using various sensors and indicators such as time-temperature indicators (TTIs), gas indicators, humidity sensors, optical, calorimetric and electrochemical biosensors. While, AP helps to increase the shelf-life of products by using absorbing and diffusion systems for various materials like carbon dioxide, oxygen, and ethanol. However, there are some important issues over these emerging technologies including cost, marketability, consumer acceptance, safety and organoleptic quality of the food and emphatically environmental safety concerns. Therefore, future researches should be conducted to solve these problems and to prompt applications of IP and AP in the food industry. This paper reviews the latest innovations in these advanced packaging technologies and their applications in food industry. The IP systems namely indicators, barcoding techniques, radio frequency identification systems, sensors and biosensor are reviewed and then the latest innovations in AP methods including scavengers, diffusion systems and antimicrobial packaging are reviewed in detail.

Application of colorimetric indicators to predict the fermentation stage of kimchi

Cabbage kimchi, a popular side dish in Korean cuisine, produces several fermentation by-products (FBPs). Kimchi is praised for its flavor, taste, and texture when suitably fermented at 0.7% to 0.9% total acidity, or a pH of approximately 4.1. Beyond this acidity level, the quality of the product decreases, negatively impacting consumers' purchase preferences. Therefore, the current study seeks to develop an optimally fermented (OptF) kimchi indicator that can be inserted into product packaging to evaluate its utility at 4 and 10 °C. A gradual change in the total color difference (ΔE) was observed during the kimchi fermentation stage, and the highest ΔE values were observed at 4 (34.87) and 10 °C (37.99), after 9 weeks. Moreover, the color-change response function value F(Xc) was more linear at 4 and 10 °C (0.981 and 0.984, respectively) compared to the ΔE over time, during kimchi fermentation. Coefficients of determination for F(Xc)-carbon dioxide (0.983), F(Xc)-pH (0.979), and F(Xc)-titratable acidity (0.974) were sufficient to meet the optimal polynomial regression model, while that for F(Xc)-lactic acid bacteria (0.881) was not. Standardized residuals of predicted data indicated that 95% of the residuals were in the range of -2.0 to 2.0. The regression analysis further suggested that the OptF kimchi indicator could be used as a kimchi fermentation indicator. PRACTICAL APPLICATION: Cabbage kimchi, a traditional Korean fermented food, produces several fermentation by-products. After the optimal fermenting stage, the sensory evaluation of cabbage kimchi and consumers' purchase preference decreases. This study describes an optimally fermented kimchi indicator and its utility at 4 and 10 °C. Our results demonstrate the ability of this indicator to predict the freshness and fermentation stage of kimchi without the need for sensory evaluation. This method could help increase the purchase preference for commercial kimchi.

Functional Polymers and Polymer-Dye Composites for Food Sensing

The sensitive, safe, and portable detection of food spoilage is becoming unprecedentedly important because it is closely related to the public health and economic development, particularly given the globalization of food supply chain. However, the existing approaches for food monitoring are still limited to meet these requirements. To address this challenge, much research has been done to develop an ideal food sensor that can indicate food quality in real-time in a sensitive and reliable way. So far, many sensors such as time-temperature indicators, smart trademarks, colorimetric tags, electronic noses, and electronic tongues, have been developed and even commercialized. In this feature article, the recent progress of food sensors based on functional polymers, including the molecular design of polymer structures, sensing mechanisms, and relevant processing techniques to fabricate a variety of food sensor devices is reviewed.