On-package dual sensors label based on pH indicators for real-time monitoring of beef freshness

High loading of anthocyanin on chitosan films by acrolein for sensitive monitoring of meat freshness

As a natural pigment, anthocyanins show different colours in a wide pH range and can be used to prepare pH-responsive smart packaging films. However, free anthocyanins have obvious disadvantages, including easy degradation under light and easy migration into foods. This study used acrolein (ACR), a highly reactive β-unsaturated aldehyde, to cross-link anthocyanin and chitosan (CS). This technique enabled loading of up to 26.18 mg/g of anthocyanin on CS, increasing the stability and preventing migration. Furthermore, acrolein substantially enhanced the mechanical strength of the film while reducing its swelling ability, water-vapour transmission and water contact angle. The film exhibited a broad range of colour shifts across pH levels ranging from 2 to 13. In ammonia simulation experiments, the film demonstrated exceptional sensitivity and quick response to volatile ammonia, exhibiting a 48.5 % colour change within 1 min. Pork freshness test also showed that when the total volatile basic nitrogen content is below 15 mg/100 g (indicating meat deterioration), the film undergoes a substantial colour change (SRGB > 40 %). Concurrently, the cross-linked anthocyanins improved the antioxidant and antibacterial activities of the membrane. Therefore, it can be concluded that the CSAP-2 film can detect pork freshness and has great application prospects in the field of smart meat packaging films.

Background-Free Imaging of Food Freshness Using Curcumin-Functionalized Upconversion Reversible Hydrogel Patch

Functionalized upconversion nanomaterials can overcome the drawbacks faced of strong background interference, photodamage, and spectral overlap by conventional optical labeling. Here, curcumin-functionalized upconversion hydrogel patch is designed with background-free and reversible for food freshness monitoring by ultra-sensitive response to biogenic amines. By loading the probes onto hydrogel patch, utilizing the good ductility to solve the problem of non-smooth surface coverage, thus accurately capturing biogenic amines. The presence of biogenic amines leads to the conversion of the diketone group on the probe to enolate ions, which triggers fluorescence resonance energy transfer (FRET) and ultimately causes the upconverted fluorescence to gradually change from green to red. The probe exhibits good detection capability for biogenic amines with a low limit of detection (LOD) of 2.73 µm. Interestingly, the patch can be restored to its initial state after water rinsing, realizing reversible detection of biogenic amines. Additionally, combining the color recognition system of smartphone can convert the imaging signal into a data signal to achieve quantitative analysis and show a reliable assessment comparable to the results of high performance liquid chromatography (HPLC). This study demonstrates the practical applicability in real-time monitoring of freshness, suggests great potential in developing optical nano-sensing strategy to ensure food safety.

A natural pigment-based nanosized colorimetric sensor for freshness evaluation of aquatic products

This work proposes an innovative method for monitoring the freshness of aquatic products using a nanosized colorimetric sensor (NCS). Six porous organic frameworks (POFs) were utilised to modify and sensitize four food-friendly natural pigments. Four optimal nano-pigments were selected based on their RGB-responsive interaction with NH3. Meanwhile, pigments exhibited significant changes in Vis-NIR spectra after nanosizing. Results indicated that the optimal NCS performs well in predicting aquatic products' total volatile alkaline nitrogen (TVB-N) content. While the prediction model based on image data did not benefit from nanosizing, the model constructed from spectral data demonstrated high accuracy and stability. The best PLS model achieved a prediction set correlation coefficient (Rp) of 0.9891 and a residual prediction deviation value of 6.66 by combining with variable combination population analysis-iteratively retaining informative variables (VCPA-IRIV) algorithm. Thus, the nanofabrication of POFs on pigments shows promise for developing high-precision and stable freshness prediction models.

Revolutionizing seafood packaging: Advancements in biopolymer smart nano-packaging for extended shelf-life and quality assurance

Food packaging is one of the most important strategies to prevent food damage or spoilage during storage and the supply chain. Among various food types, seafood, a high-value product, is particularly vulnerable to post-harvest quality loss and microbial contamination during storage. Although current plastic-based packaging materials are durable, they pose a serious threat to the environment. Therefore, research on natural biopolymers for packaging is a top priority for scientists, industries, and government bodies. Additionally, nanoengineering concepts enhance the physicochemical and functional properties of biopolymers, thereby revolutionizing the packaging industry. This review provides a comprehensive discussion on smart nano-packaging for seafood products. It focuses on advancements in biopolymer smart nano-packaging as a transformative solution for extending the shelf life and ensuring the quality of seafood products. Existing knowledge highlights the functionality of biopolymers and nanotechnology, but gaps remain in addressing practical applications, such as scalability, cost-efficiency, and consumer safety. This review bridges these gaps by providing a detailed analysis of biopolymer-based active and intelligent packaging systems, which integrate antioxidant, antimicrobial, and freshness-indicating properties. It emphasizes the unique contributions of nanoengineering to enhance biopolymer properties, offering innovative solutions to the seafood packaging industry while promoting environmental sustainability.

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.

P-type accumulation mode organic electrochemical transistor biosensor for xanthine detection in fish

Food waste is a global challenge that needs to be mitigated in the development of more sustainable societies. From manufacturers to customers, food biosensors could effectively reduce the amount of discarded food and provide more precise predictions of freshness with respect to pre-decided expiration dates. In this study, we developed a novel organic electrochemical transistor (OECT)-based xanthine biosensor. The OECT-based biosensor is based on the p-type conjugated polymer, p(g42T-TT) as the channel, and incorporated xanthine oxidase (XOD) as the biorecognition element. The OECT thus acts as a transducer and amplifier of the enzymatic oxidation of xanthine. Real-time monitoring of xanthine using the OECT-based biosensor led to a linear range between 5 and 98 μM (R2=0.989), 3.28 μM limit of detection, and high sensitivity up to 21.8 mA/mM. Real sample tests showed that the biosensor can detect the accumulation of xanthine in fish meat from 0 to 6 days of degradation. Interference tests with ascorbic acid and uric acid and spike-and-recovery tests with fish samples indicated that as-designed biosensors have good selectivity and accuracy. The developed biosensors show great potential for point-of-care testing applied to food monitoring.

Stimuli-responsive carrageenan-based biomaterials for biomedical applications

Carrageenan-based biomaterials have attracted considerable attention in recent years due to their unique biological properties, including their biodegradability, compatibility, and lack of adverse effects. These biomaterials exhibit a variety of beneficial properties, such as antiviral, antitumor, and immunomodulatory effects, which set them apart from other polysaccharides. Stimuli-responsive carrageenan-based biomaterials have attracted particular attention due to their unique properties, such as reducing systemic toxicity and controlling drug release. In this review, a comprehensive investigation of stimuli-responsive carrageenan-based biomaterials was conducted under the influence of various stimuli such as pH, electric field, magnetic field, temperature, light, and ions. These structures exhibited good stimulus-responsive properties and involved corresponding physical and chemical changes, such as changes in swelling ratio and gelling power among others. The biomedical application of carrageenan-based stimuli-responsive biomaterials in the field of tissue engineering, anticancer, antibacterial, and food monitoring has been investigated, showing the great potential of these structures. Although there are promising developments in the design and use of stimuli-responsive carrageenan-based biomaterials, further research is advisable to further investigate their potential applications, particularly in animal models. Extensive studies are needed to investigate the benefits and limitations of these materials to ensure their safety and effective use in biomedical applications.

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.

Enhancing seafood freshness monitoring: Integrating color change of a food-safe on-package colorimetric sensor with mathematical models, microbiological, and chemical analyses

The study assessed a developed food-safe on-package label as a real-time spoilage indicator for fish fillets. This colorimetric sensor is sensitive to Total Volatile Base Nitrogen (TVB-N) levels, providing a correct indication of fish freshness and spoilage. This study evaluates and predicts the shelf-life and effectiveness of an on-package colorimetric indicator. The sensor, using black rice (BC) dye with polyvinyl alcohol (PVOH), polyethylene glycol (PEG), and citric acid (CA) as binders and crosslinking agents, is applied to PET films. The food-safe pH indicator, prepared via lab-scale flexography printing, is durable in humid environments, making it suitable for practical packaging scenarios. The sensor visibly monitored fish spoilage at 4 °C for 9 days. Quality assessment included tracking ΔRGB (total color difference), chemical (TVB-N, pH), and microbiological analyses. Results indicate that the fish samples are fresh up to 4 days of storage at 4 °C; the total viable count (TVC), Pseudomonas growth, TVB-N contents and pH reached: 5.2 (log CFU/ml), 4.31(log CFU/ml), 26.22 (mg N/100 gr sample) and 7.48, respectively. Integrating colorimetric sensor data with mathematical modeling can predict spoilage trends over time. Integrated system offers a smart approach to accurately predicting shelf-life, aiding in optimizing storage conditions, minimizing food waste, and delivering fresh, high-quality fish products to consumers.

Development of konjac glucomannan-based active-intelligent emulsion films loaded with different curcumin-metal chelates: Stability, antioxidant, fresh-keeping and freshness detection properties

The aim of this study was to develop konjac glucomannan (KGM)-based active-intelligent emulsion films loaded with different curcumin-metal chelates, where six types of films were prepared and their corresponding properties were investigated. The FTIR and XRD results showed that curcumin chelated with metal ions successfully. Moreover, curcumin-Ca chelate had the best thermal stability and antioxidant activity with the DPPH and ABTS radical-scavenging activity values of 38.28 % and 22.79 %, respectively. Furthermore, the results of microstructure and contact angle showed that chelation with metal ions improved the interfacial interactions between curcumin-metal chelates and film matrix. Interestingly, KGM-based active-intelligent emulsion films loaded with curcumin-Ca chelate (Type IV film) displayed the best thermal stability with the highest temperature of maximum weight loss at 380 °C, the best mechanical property, the highest total phenol content (17.31 mg gallic acid/g film), as well as the best antioxidant activity with DPPH and ABTS radical-scavenging activity values of 69.24 % and 58.66 %, respectively, and the best antibacterial activity. Consequently, Type IV film was used for the fresh-keeping and freshness detection of pork. The results showed that the pork packaged with Type IV film displayed excellent fresh-keeping properties, including reducing the increase rate of volatile basic nitrogen (TVB-N) and pH values and the decrease rate of hardness and elasticity of pork during storage time. Meanwhile, the color of Type IV film gradually changed from yellow to red. Therefore, this study suggested that KGM-based active-intelligent emulsion films have great potential application in the fresh-keeping and freshness detection of fresh meat.

Monitoring Meat Freshness with Intelligent Colorimetric Labels Containing Red Cabbage Anthocyanins Copigmented with Gelatin and Gallic Acid

Polyvinyl alcohol (PVA)-based pH-responsive color indicators were developed using red cabbage anthocyanin (Anth) copigmented with gelatin and gallic acid (GA). The indicator prepared with gelatin and GA (GA/gelatin/Anth/PVA) was highly resistant to light exposure. GA/gelatin/Anth/PVA exhibited distinct color changes in pH 2-11 buffer solutions and stable color indication in acidic and neutral solid systems (pH 2 and 7) at 97% relative humidity. GA/gelatin/Anth/PVA exhibited the highest sensitivity to dimethylamine, followed by ammonia and trimethylamine. The addition of gelatin and GA facilitated hydrogen bonding, which enhanced thermal stability and water solubility without compromising tensile properties. A color change from purple to blue signaled spoilage when total volatile basic nitrogen values for beef and squid reached 21.0 and 37.8 mg/100 g, respectively. The GA/gelatin/Anth/PVA indicator shows potential for indicating the freshness of raw beef.

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.

Towards Reducing Food Wastage: Analysis of Degradation Products Formed during Meat Spoilage under Different Conditions

Foodstuffs, particularly perishable ones such as meat, are frequently discarded once the best-before date has been reached, despite the possibility of their continued suitability for human consumption. The implementation of intelligent packaging has the potential to contribute to a reduction in food wastage by enabling the monitoring of meat freshness during storage time independently of the best-before date. The process of meat spoilage is associated with the formation of specific degradation products, some of which can be potentially utilized as spoilage indicators in intelligent packaging. The aim of the review is to identify degradation products whose concentration correlates with meat shelf life and to evaluate their potential use as spoilage indicators in intelligent packaging. To this end, a comprehensive literature research was conducted to identify the factors influencing meat spoilage and the eight key degradation products (carboxylic acids, biogenic amines, total volatile basic nitrogen, aldehydes, alcohols, ketones, sulfur compounds, and esters) associated with this process. These degradation products were analyzed for their correlation with meat shelf life at different temperatures, atmospheres, and meat types and for their applicability in intelligent packaging. The review provides an overview of these degradation products, comparing their potential to indicate spoilage across different meat types and storage conditions. The findings suggest that while no single degradation product universally indicates spoilage across all meat types and conditions, compounds like carboxylic acids, biogenic amines, and volatile basic nitrogen warrant further investigation. The review elucidates the intricacies inherent in identifying a singular spoilage indicator but underscores the potential of combining specific degradation products to expand the scope of applications in intelligent packaging. Further research (e.g., storage tests in which the concentrations of these substances are specifically examined or research on which indicator substance responds to these degradation products) is recommended to explore these combinations with a view to broadening their applicability.

Real-time monitoring of pork freshness using polyvinyl alcohol/modified agar multilayer gas-sensitive labels

Accurate consumer perception of food packages should provide real-time feedback on any changes inside food packaging. Hence, a new multilayer gas-sensitive label (POA-12) was prepared using a layer-by-layer pouring method for simple, visual, and real-time detection of pork's freshness, while the front side was developed by immobilizing red carbon dots and fluorescein isothiocyanate in POA as indicator for volatile nitrogen, and the back side was created using bromothymol blue in POA as pH indicator. The swelling index of the multilayer gas-sensitive labels reduced from 159.19% to 148.36%, and the tensile strength increased from 25.52 MPa to 42.61 MPa. In addition, the POA-12 multilayer label showed a red-to-yellow fluorescence change as TVB-N increased from 6.84 to 31.4 and a yellow-brown-to-blue-green color change as pH increased from 5.74 to 7.24 when detecting pork samples. Thus, it provides dual-indicator monitoring that improves the accuracy and reliability of assessing the freshness of high-protein products.

Recent advancements in chitosan-based intelligent food freshness indicators: Categorization, advantages, and applications

With an increasing emphasis on food safety and public health, there is an ongoing effort to develop reliable, non-invasive methods to assess the freshness of diverse food products. Chitosan-based food freshness indicators, leveraging properties such as biocompatibility, biodegradability, non-toxicity, and high stability, offer an innovative approach for real-time monitoring of food quality during storage and transportation. This review introduces intelligent food freshness indicators, specifically those utilizing pH-sensitive dyes like anthocyanins, curcumin, alizarin, shikonin, and betacyanin. It highlights the benefits of chitosan-based intelligent food freshness indicators, emphasizing improvements in barrier and mechanical properties, antibacterial activity, and composite film solubility. The application of these indicators in the food industry is then explored, alongside a concise overview of chitosan's limitations. The paper concludes by discussing the challenges and potential areas for future research in the development of intelligent food freshness indicators using chitosan. Thus, chitosan-based smart food preservation indicators represent an innovative approach to providing real-time data for monitoring food quality, offering valuable insights to both customers and retailers, and playing a pivotal role in advancing the food industry.

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.

Development of a Freshness Indicator for Assessing the Quality of Packaged Pork Products during Refrigerated Storage

A pH-sensitive dye-based freshness indicator has been developed to monitor the quality status of pork neck through distinct color transitions, addressing a crucial need for improved food safety and real-time monitoring within the food industry. This system aims to boost consumer confidence and improve shelf-life estimates by offering transparent and immediate quality indicators. Aerobically packaged pork neck samples underwent accelerated testing at 25 °C for 36 h, followed by refrigeration experiments at typical distribution temperatures of 4 and 8 °C over 10 days. Measured pork neck quality parameters included total bacterial count (TBC), total volatile basic nitrogen (TVB-N), and pH levels. Visual observation and colorimetric analysis were used to assess the chromatic variations of the freshness indicator, which showed a significant shift from orange to green in response to the presence of TVB-N in the headspace of the pork packaging. The chromatic parameters of the freshness indicator exhibited a significant correlation with the pork quality values throughout the storage periods. The results highlight the ability of the freshness indicator to effectively convey quality information about pork through noticeable colorimetric changes.

Potato oxidized hydroxypropyl starch/pectin-based indicator film with Clitoria ternatea anthocyanin and silver nanoparticles for monitoring chilled beef freshness

Potato oxidized hydroxypropyl starch (POHS)/pectin (P) functional and smart beef freshness indicator films were prepared using butterfly pea (Clitoria ternatea) anthocyanin (BA) and silver nanoparticles (AgNPs). BA exhibited significant pH-responsive color changes. BA and AgNPs were evenly distributed within a polymer matrix to create a compatible film with POHS/P. The films containing BA and AgNPs had good UV resistance and maintained strong mechanical strength, barrier properties, and color stability. The color of the indicator film changed from purple to green when exposed to ammonia, with the 1 % POHS/P/BA/AgNPs film showing the most sensitive response. The films also demonstrated strong antibacterial and antioxidant properties. The freshness of beef was monitored using 1 % POHS/P/BA/AgNPs films and was identified as sub-fresh and spoiled on days 4 and 7, respectively. The relationship between the color change of the indicator label and the freshness of chilled beef was established: purple for fresh meat, blue for less fresh meat, and green for spoiled meat. Thus, the new POHS/P/BA/AgNPs film can serve as a smart packaging material to indicate food freshness and extend shelf life. These results suggest that POHS/P/BA/AgNPs films have significant potential as an active and smart food packaging material.

Reusable, Green, Portable Ionogels Based on Terpyridine-Imidazole Salt for Visual Monitoring of Pork Spoilage

Ionogels have emerged as a promising approach because they combine the advantageous properties of ionic liquids and gels. Herein, a novel gelator bearing terpyridine and imidazolium salt units was designed and synthesized, which assembled into ionogels in three ionic liquids by a heating-cooling procedure. The properties of ionogels were characterized by FT-IR, UV-vis spectroscopy, POM, XRD, and rheology, and resonance light scattering and opacity measurements were conducted to investigate the gelation kinetics. Furthermore, the ionogels incorporating pH-sensitive dyes (BTB and MR) were exploited as colorimetric sensor to monitor total volatile basic nitrogen (TVB-N) of meat at -4 °C, which can easily and reliably estimate the quality of meat by naked eye recognition, and the results demonstrated a positive correlation between the color variation and TVB-N levels. Notably, the hydrophobic ionogel indicators are more suitable for potential application at high humidity thanks to their antiswelling advantage, which could prevent the inaccurate information produced by hydrogel indicators. In addition, the ionogels could be reused up to three times as colorimetric indicators, suggesting potential applications and competitiveness. Our research sheds new light on the novel application of ionogels in the food industry.

Ammonia-responsive chitosan/polymethacrylamide double network hydrogels with high-stretchability, fatigue resistance and anti-freezing for real-time chicken breast spoilage monitoring

Hydrogels are a promising option for detecting food spoilage in humid conditions, but current indicators are prone to mechanical flaws, posing a concern for packaging systems that require strong mechanical properties. Herein, a double network hydrogel was prepared by polymerizing methacrylamide in a chitosan system with aluminum chloride and glycerol. The resulting hydrogel demonstrated high stretchability (strain >1500 %), notch insensitivity, excellent fatigue resistance, and exceptional anti-freezing capabilities even at -21 °C. When incorporating bromothymol blue (BB) or methyl red (MR), or mixtures of these dyes into the hydrogels as indicators, they exhibited sensitive colorimetric responses to pH and NH3 levels at different temperatures. Hydrogels immobilizing BB to MR ratios of 1:1 and 1:2 displayed clearer and more sensitive color responses when packed into chicken breast, with a sensitivity level of 1.5 ppm of total volatile basic nitrogen (TVB-N). This color response correlated positively with the accumulation of TVB-N on the packaging during storage at both 25 °C and 4 °C, providing sensitive indications of chicken breast deterioration. Overall, the developed hydrogels and indicators demonstrate enhanced performance characteristics, including excellent mechanical strength and highly NH3-sensitive color responses, making significant contributions to the food spoilage detection and intelligent packaging systems field.

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.

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.

Rapid and visual evaluation the internal corruption of meat tissue by a designed near-infrared fluorescence probe with a broad pH response range

Rapid and visual evaluation the internal corruption of meat tissue is closely related to public health. The pH change caused by glycolysis and amino acid decomposition is an important indicator of meat freshness. Herein, we designed a pH-responsive NIR fluorescent probe (Probe-OH) based on protonation/deprotonation for monitoring the internal corruption of meat tissue. Probe-OH was synthesized by a stable hemicyanine skeleton with phenolic hydroxyl group, which exhibited excellent performances such as high selectivity, high sensitivity, fast response time (60 s), a broad pH-responsive range of 4.0-10.0, and superior spatio-temporal sampling ability. In addition, we conducted a paper chip platform to measure pH value in different meat samples (pork and chicken), which is convenient to evaluate pH value of meat by observing the color changes of paper strips. Furthermore, in combination with the NIR advantages of fluorescence imaging, Probe-OH was successfully applied to assess the freshness of pork and chicken breasts, and the structural changes of muscle tissue can be clearly observed under confocal microscope. The results of Z-axis scanning showed that Probe-OH could penetrate into the interior to monitor the internal corruption of meat tissue, the fluorescence intensity changes with scanning height in the meat tissue section, and reaches its maximum at 50 μm. To the best of our knowledge, there have been no reports of fluorescence probe being used to image the inside of meat tissue section so far. It is expected that we can provide a new rapid, sensitive, near-infrared fluorescence method for assessment of the freshness in the internal organization of meat.

The colorful world of sulfonephthaleins: Current applications in analytical chemistry for "old but gold" molecules

Sulfonephthaleins represent one of the most common and widely employed reactive dyes in analytical chemistry, thanks to their stability, low-cost, well-visible colors, reactivity and possibilities of chemical modification. Despite being first proposed in 1916, nowadays, these molecules play a fundamental role in biological and medical applications, environmental analyses, food quality monitoring and other fields, with a particular focus on low-cost and disposable devices or methods for practical applications. Since up to our knowledge, no reviews or book chapters focused explicitly on sulfonephthaleins have ever been published, in this review, we will briefly describe sulfonephthaleins history, their acid-base properties will be discussed, and the most recent applications in different fields will be presented, focusing on the last ten years literature (2014-2023). Finally, safety and environmental issues will be briefly discussed, despite being quite controversial.

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.

The Development of Highly pH-Sensitive Bacterial Cellulose Nanofibers/Gelatin-Based Intelligent Films Loaded with Anthocyanin/Curcumin for the Fresh-Keeping and Freshness Detection of Fresh Pork

The aim of this study was to develop highly pH-sensitive bacterial cellulose nanofibers/gelatin-based intelligent films, where the intelligent films were loaded with different ratios (10:0, 0:10 2:8, 5:5 and 8:2, w/w) of curcumin:anthocyanin (Cur/ATH), and the characterization of intelligent films was investigated. The results showed that the microstructures of intelligent films were much rougher as the proportion of curcumin increased. FTIR results showed that anthocyanin and curcumin were fixed in gelatin matrix by hydrogen bonds. Moreover, XRD results showed that curcumin had a significant effect on the crystal structure of the films. Interestingly, films loaded with a Cur/ATH ratio of 5:5 had the best mechanical and antioxidant properties and a high pH-sensitivity property. Consequently, the bacterial cellulose nanofibers/gelatin-based intelligent films loaded with a Cur/ATH ratio of 5:5 were used for the packaging of fresh pork, displaying good fresh-keeping and freshness detection effects. Therefore, this study suggested that bacterial cellulose nanofibers/gelatin-based intelligent films have great potential in the fresh-keeping and freshness detection of meat.

Applicability and Freshness Control of pH-Sensitive Intelligent Label in Cool Chain Transportation of Vegetables

Freshness is one of the main factors affecting consumers' purchase of food. The freshness indicator labels of packaged fresh green bell pepper (Capsicum annuum L.) and greengrocery (Brassica chinensis L.) were constructed, and pH-sensitive indicator labels based on the dye of anthocyanin and the mixing dye of methyl red and bromothymol blue were prepared in this study. At the same time, the color, chlorophyll content and vitamin C content of vegetables were measured in order to explore the applicability of indicator labels in the cool chain transportation of vegetables. Compared with the nature dye, the chemical dye-type indicator labels are more sensitive to pH changes. The results showed that the mixed indicator intelligent label had the best indication effect, and the MB 2 (mixing 1 g/L methyl red and bromothymol blue solutions at a ratio of 3:2 with a concentration of 70 mL/L in indicator film solution) indicator label could effectively indicate the freshness changes in vegetables during storage. Meanwhile, the color changes of the MB 2-type indicator label were correlated with the colors change of the sample, changes in nutrients, and changes in CO2 content inside the packaging. In addition, freshness detection models for green bell pepper and greengrocery by using color information of MB 2 intelligent labels were established. Hence, this pH-sensitive label can be applied as a promising intelligent packaging for non-destructively monitoring the freshness of respiratory and non-respiratory climacteric vegetables.

Applications, challenges and prospects of bionic nose in rapid perception of volatile organic compounds of food

Bionic nose, a technology that mimics the human olfactory system, has been widely used to assess food quality due to their high sensitivity, low cost, portability and simplicity. This review briefly describes that bionic noses with multiple transduction mechanisms are developed based on gas molecules' physical properties: electrical conductivity, visible optical absorption, and mass sensing. To enhance their superior sensing performance and meet the growing demand for applications, a range of strategies have been developed, such as peripheral substitutions, molecular backbones, and ligand metals that can finely tune the properties of sensitive materials. In addition, challenges and prospects coexist are covered. Cross-selective receptors of bionic nose will help and guide the selection of the best array for a particular application scenario. It provides an odour-based monitoring tool for rapid, reliable and online assessment of food safety and quality.

An antibacterial and intelligent cellulose-based label self-assembled via electrovalent bonds for a multi-range sensing of food freshness

Intelligent labels provide customers with food freshness information. However, the existing label response is limited and can only detect a single kind of food. Here, an intelligent cellulose-based label with highly antibacterial activity for a multi-range sensing freshness was developed to overcome the limitation. Cellulose fibers were modified using oxalic acid to graft -COO^- followed by binding chitosan quaternary ammonium salt (CQAS), the remaining charges of which attached methylene red and bromothymol blue to form response fibers and to further self-assemble into the intelligent label. CQAS electrostatically gathered the dispersed fibers, resulting in an increase in TS and EB of 282 % and 16.2 %, respectively. After that, the rest positive charges fixed the anionic dyes to broaden pH response range of 3-9 effectively. More significantly, the intelligent label exhibited highly antimicrobial activity, killing 100 % of staphylococcus aureus. The rapid acid-base response revealed the potential for practical application in which the label color from green to orange represented the milk or spinach from fresh to close to spoiled, and from green to yellow, and to light green indicated the pork fresh, acceptable, and close to spoiled. This study paves a way for the preparation of intelligent labels in large-scale and promote the commercial application to improve food safety.

Highly sensitively detection of amine vapors released during shrimp spoilage by fluorescent molecules locked in covalent organic frameworks

The fluorescent sensors allow sensitive detection of amine vapors for assessing the safety and quality of seafood products. However, high diffusion resistance and insufficient recognition sites usually limit the sensitivity of the sensors. Here, we employed an emulsion-confined assembly strategy to uniform encapsulate fluorescent molecules perylene diimide (PDI) molecules into covalent organic frameworks (COFs) to achieve ultrasensitive detection of amine vapors. The detection mechanism is based on the photoinduced electron transfer from amine to the excited PDI. This method exhibits a broad linear detection range from 8 ppb to 800 ppm and the limit of detection reaches as low as 1.2 ppb. The real-time detection of the amine vapors produced during shrimp spoilage is successfully achieved with excellent performance. This provides a versatile method for the on-demand synthesis of functional materials with high fluorescence properties for the development of chemical sensors via encapsulating different fluorescent molecules into COFs.

Halochromic Textiles for Real-Time Sensing of Hazardous Chemicals and Personal Protection

Chemical protective clothing (CPC) has become mandatory when performing various tasks to ensure user protection and prevent chemicals from contacting the skin and causing severe injuries. In addition to protection, there is a need to develop a simple mechanism that can be attached to CPC and be capable of detecting and alerting the user to the presence of harmful chemical agents. In this study, a double-sensor strategy was investigated, using six different pH indicators stamped on cotton and polyester knits to detect acidic and alkaline substances, both liquid and gaseous. Functionalized knits underwent microscopic characterization, air permeability and contact angle evaluation. All samples exhibited hydrophobic behavior (contact angle > 90°) and air permeability values above 2400 L/min/cm²/bar, with the best condition demonstrating a contact angle of 123° and an air permeability of 2412.5 L/min/cm²/bar when the sensor methyl orange and bromocresol purple (MO:BP) was stamped on polyester. The performed tests proved the functionality of the sensors and showed a visible response of all knits when contacting with different chemicals (acids and bases). Polyester functionalized with MO:BP showed the greatest potential, due to its preeminent color change. Herein, the fiber coating process was optimized, enabling the industrial application of the sensors via a stamping method, an alternative to other time- and resource-consuming techniques.

Sensing materials for fresh food quality deterioration measurement: a review of research progress and application in supply chain

Fresh food are consumed in large quantities worldwide. During the supply chain, microbial growth in fresh food can lead to the production of a number of metabolites, which make food highly susceptible to spoilage and contamination. The quality of fresh food changes in terms of smell, tenderness, color and texture, which causes a decrease in freshness and consumers acceptance. Therefore, the quality monitoring of fresh food has become an essential part in the supply chain. As traditional analysis methods are highly specialized, expensive and have a small scope of application, which cannot be applied to the supply chain to realize real-time monitoring. Recently, sensing materials have received a lot of attention from researchers due to the low price, high sensitivity and high speed. However, the progress of research on sensing materials has not been critically evaluated. The study examines the progress of research in the application of sensing materials for fresh food quality monitoring. Meanwhile, indicator compounds for spoilage of fresh food are analyzed. Moreover, some suggestions for future research directions are given.

Utilization of Food Waste and By-Products in the Fabrication of Active and Intelligent Packaging for Seafood and Meat Products

Research on the utilization of food waste and by-products, such as peels, pomace, and seeds has increased in recent years. The high number of valuable compounds, such as starch, protein, and bioactive materials in waste and by-products from food manufacturing industries creates opportunities for the food packaging industry. These opportunities include the development of biodegradable plastics, functional compounds, active and intelligent packaging materials. However, the practicality, adaptability and relevance of up-scaling this lab-based research into an industrial scale are yet to be thoroughly examined. Therefore, in this review, recent research on the development of active and intelligent packaging materials, their applications on seafood and meat products, consumer acceptance, and recommendations to improve commercialization of these products were critically overviewed. This work addresses the challenges and potential in commercializing food waste and by-products for the food packaging industry. This information could be used as a guide for research on reducing food loss and waste while satisfying industrial demands.

Quality and Shelf-Life Evaluation of Fresh Beef Stored in Smart Packaging

Beef is a perishable food product susceptible to deterioration due to microbial growth. Therefore, this study aimed to ascertain how active and intelligent packaging performs by tracking the change in the quality of fresh beef stored at low temperatures. The intelligent packaging method employed indicators with solutions of Bromo Phenol Blue (BPB) and Phenol Red (PR) to monitor the change in beef quality. Additionally, active packaging used garlic extract with various concentrations at 0%, 15%, and 20% to maintain the quality of beef packaged at 10 °C temperatures. The findings illustrated that a packaging indicator label can be implemented to monitor the change in the quality of fresh beef stored at 10 °C temperatures. This was signified by a change in the indicator color from dark yellow to orange and red, fading to purple. Meanwhile, observations on active packaging demonstrated that 15% and 20% of garlic extract were the most effective approaches for preserving beef quality. The correlation level of indicator label color analysis and the effectiveness of active packaging with all beef spoilage metrics demonstrated a positive correlation in preserving quality and identifying the degree of beef damage. Therefore, these active and intelligent packaging indicators can be applied to monitor and retain the quality of packaged beef.

Application of intelligent packaging for meat products: A systematic review

BACKGROUND

Today, in response to consumer demand and market trends, the development of new packaging with better performance such as intelligent packaging has become more important. This packaging system is able to perform intelligent functions to increase shelf life, increase safety and improve product quality.

OBJECTIVES

Recently, various types of packaging systems are available for meat products, especially cooked, fresh and processed meats. But because meat products are very perishable, monitoring their quality and safety in the supply chain is very important. This systematic article briefly reviews some of the recent data about the application of intelligent packaging in meat products.

METHODS

The search was conducted in Google Scholar, Science Direct, Elsevier, Springer, Scopus, and PubMed, from April 1996 to April 2021 using a different combination of the following keyword: intelligent packaging, and meat.

RESULTS

The results showed that the intelligent packaging presents several benefits compared to traditional packaging (e.g., antimicrobial, antioxidant, and shelf life extension) at the industrial processing level. Thus, these systems have been applied to improve the shelf life and textural properties of meat and meat products.

CONCLUSIONS

It is necessary to control the number of intelligent compounds that are included in the packaging as they clearly influence the quality and nutritional properties as well as the final cost of the food products.

Intelligent pH indicator composite film based on pectin/chitosan incorporated with black rice anthocyanins for meat freshness monitoring

With the improvement of consumer awareness of food safety and the increasing concern about plastic pollution, the development of novel intelligent packaging film is imminent. This project aims to develop an environmentally friendly pH-sensitive intelligent food packaging film for meat freshness monitoring. In this study, anthocyanin-rich extract from black rice (AEBR) was added to composite film formed by the co-polymerisation of pectin and chitosan. AEBR showed strong antioxidant activity, and different colour responses to different conditions. The mechanical properties of the composite film remarkably improved when AEBR was incorporated into. Besides, the introduction of anthocyanins enables the colour of composite film to change from red to blue with the degree of meat spoilage increased which shows the indicative effect of composite films on meat putrification. Therefore, the AEBR-loaded pectin/chitosan film could be used as an indicator to monitor meat freshness in real-time.

Polyvinyl alcohol/starch-based film incorporated with grape skin anthocyanins and metal-organic framework crystals for colorimetric monitoring of pork freshness

An intelligent film for the visual monitoring of pork freshness was developed using degradable polyvinyl alcohol (PVA)/starch (PS) to immobilize the chromogenic agent of anthocyanins and the volatile amine collector of metal-organic frameworks (MOFs). The indicative property of grape skin anthocyanins (GSAs) was verified using the UV-vis spectra, corresponding to multi-color changing in a pH range of 2-12. Interestingly, the introduction of MIL-101 crystals in the PS/GSAs film significantly increased the specific surface area (approximately 10 times) of the film, the superior volatile amine enrichment capability of MIL-101 enabling the film to detect freshness with a high degree of sensitivity. Moreover, the as-prepared film exhibited good antibacterial properties attributed to MIL-101, which help maintain the freshness of the pork. Owing to these advantages, the PS-GSAs/MIL-101 film was tested to real-timely monitor pork freshness in package, the results were further confirmed basis the total volatile basic nitrogen values.

Development of Smart Bilayer Alginate/Agar Film Containing Anthocyanin and Catechin-Lysozyme

Smart packaging can provide real-time information about changes in food quality and impart a protective effect to the food product by using active agents. This study aimed to develop a smart bilayer film (alginate/agar) with a cellulose nanosphere (CNs) from corncob. The bilayer films were prepared using 1.5% (w/w) sodium alginate with 0.25% (w/v) butterfly pea extract incorporated (indicator layer) and 2% (w/w) agar containing 0.5% (w/v) catechin−lysozyme (ratio 1:1) (active layer). The CNs were incorporated into the alginate layer at different concentrations (0, 5, 10, 20, and 30% w/w-based film) in order to improve the film’s properties. The thickness of smart bilayer film dramatically increased with the increase of CNs concentration. The inclusion of CNs reduced the transparency and elongation at break of the smart bilayer film while increasing its tensile strength (p < 0.05). The integration of CNs did not significantly affect the solubility and water vapor permeability of the smart bilayer film (p > 0.05). The smart bilayer film displayed a blue film with a glossy (without CNs) or matte surface (with CNs). The developed bilayer film shows excellent pH sensitivity, changing color at a wide range of pHs, and has a good response to ammonia and acetic acid gases. The film possesses exceptional antimicrobial and antioxidant activities. The integration of CNs did not influence the antibacterial activity of the film, despite the presence of a higher level of DPPH in film containing CNs. The smart bilayer film was effectively used to monitor shrimp freshness. These findings imply that smart bilayer films with and without CNs facilitate food safety and increase food shelf life by monitoring food quality.

Development and Application of Dual-Sensors Label in Combination with Active Chitosan-Based Coating Incorporating Yarrow Essential Oil for Freshness Monitoring and Shelf-Life Extension of Chicken Fillet

This study aimed for the application of active chitosan coating incorporating yarrow essential oil (YEO) together with the development of an on-package sensor label based on bromocresol purple (BCP) and methyl red (MR) for shelf-life extension and freshness monitoring of chicken breast fillet. Physiochemical and microbiological attributes of chicken meat coated with sole chitosan, YEO, and chitosan + YEO were compared with those of uncoated (control) samples. Chitosan + YEO coated chicken meat stayed fresh with no significant changes (p > 0.05) in pH (5.42−5.56), TVB-N (12.55−15.36 mg N/100 g), TBARs (0.35−0.40 mg MDA/kg) and total aerobic psycrotrophic bacteria (3.97−4.65 log CFU/g) in days 1−15. There was no response of the dual-sensors label toward the variation in chemical and microbiological indicators of chicken meat coated with chitosan + YEO. However, either uncoated, sole chitosan, or sole YEO treatments indicated a three-stage freshness status with the fresh stage belonged to a period earlier than day 7 (with no distinct color change in both sensor labels); the semi-fresh stage corresponded to storage days between 7−9, wherein a gradual color change appeared (MR from pink to orange, BCP from yellow to light purple); and the spoiled stage occurred in day 9 onward with a drastic color change (MR from orange to light yellow, BCP from light purple to deep purple). In general, the dual-sensors successfully responded to the variation of chemical and microbiological indicators and visual color of uncoated samples during storage time. Based on the obtained results, the application of chitosan + YEO coating efficiently prolonged the freshness of chicken breast meat, where on-package dual-sensors systems were able to detect the freshness stages of meat samples during storage time.

On-package ratiometric fluorescent sensing label based on AIE polymers for real-time and visual detection of fish freshness

Freshness is an important parameter of fish quality. This study aims to develop a ratiometric fluorescent sensing label that is responsive to volatile amines, affording real-time and visual detection of fish freshness. For developing of the sensing label, an aggregation-induced emissive (AIE) polymer was prepared from the stimuli-responsive polymer polymethacrylic acid and the AIE molecule tetraphenylethylene and coated on to filter paper with rhodamine B as an internal reference. By exploiting the ratiometric response, the freshness of fish could be identified clearly and easily according to the color of on-package label, which changes from pink (fresh) to dark blue. The difference was linearly correlated with the total volatile basic nitrogen (TVB-N, R² = 0.995 and 0.994 at 25 °C and 4 °C, respectively) in the range of 15-25 mg/100 g for the salmon samples, which indicated that the sensing label feasibly and non-destructively quantified TVB-N.

Halochromic Inks Applied on Cardboard for Food Spoilage Monitorization

Control of food spoilage is a critical concern in the current world scenario, not only to ensure the quality and safety of food but also to avoid the generation of food waste. This paper evaluates a dual-sensor strategy using six different pH indicators stamped on cardboard for the detection of spoilage in three different foods: beef, salmon, and strawberries. After function validation and formulation optimizations in the laboratory, the halochromic sensors methyl orange and bromocresol purple 2% (w/v) were stamped on cardboard and, in contact with the previously mentioned foods, were able to produce an easily perceptible signal for spoilage by changing color. Additionally, when it comes to mechanical characterization the inks showed high abrasion (>100 cycles) and adhesion resistance (>91%).

Recent Progress in Amine Gas Sensors for Food Quality Monitoring: Novel Architectures for Sensing Materials and Systems

The increasing demand for food production has necessitated the development of sensitive and reliable methods of analysis, which allow for the optimization of storage and distribution while ensuring food safety. Methods to quantify and monitor volatile and biogenic amines are key to minimizing the waste of high-protein foods and to enable the safe consumption of fresh products. Novel materials and device designs have allowed the development of portable and reliable sensors that make use of different transduction methods for amine detection and food quality monitoring. Herein, we review the past decade's advances in volatile amine sensors for food quality monitoring. First, the role of volatile and biogenic amines as a food-quality index is presented. Moreover, a comprehensive overview of the distinct amine gas sensors is provided according to the transduction method, operation strategies, and distinct materials (e.g., metal oxide semiconductors, conjugated polymers, carbon nanotubes, graphene and its derivatives, transition metal dichalcogenides, metal organic frameworks, MXenes, quantum dots, and dyes, among others) employed in each case. These include chemoresistive, fluorometric, colorimetric, and microgravimetric sensors. Emphasis is also given to sensor arrays that record the food quality fingerprints and wireless devices that operate as radiofrequency identification (RFID) tags. Finally, challenges and future opportunities on the development of new amine sensors are presented aiming to encourage further research and technological development of reliable, integrated, and remotely accessible devices for food-quality monitoring.

Facile monitoring of meat freshness with a self-constructed photosensitization colorimetric instrument

Total volatile basic nitrogen (TVB-N) produced from the decomposition of amino acids is an important indicator for meat freshness. Various pH-sensitive colorimetric films have been incorporated as intelligent packaging for meat freshness during food transportation. However, methods and instruments capable of on-site end-point detection of meat freshness are still needed for places that provide raw meat without packaging. Herein, based on amine-induced pH change that led to decreased color output of the 3,3',5,5'-tetramethylbenzidine (TMB)-based photosensitization colorimetric assay, a simple yet convenient instrument employing colorimetric indicator paper (CIP) was constructed for facile monitoring of meat freshness. Owing to the background color provided by the photosensitizer erythrosine (2',4',5',7'-tetraiodofluorescein, TIF), the color changed from blue to pink upon amine adsorption. A bespoke cellphone App was employed for image capture and color analysis of the CIP for freshness monitoring. The analytical results of amine (released from meat during storage) by the proposed method agreed well with those by a standard Conway dish method. In addition, the whole analytical process could be completed in about 5 min. The developed instrument may be potentially useful for on-site monitoring of meat freshness.