Preparation of a shikonin-based pH-sensitive color indicator for monitoring the freshness of fish and pork

Enhancing sensitivity and stability of natural pigments in pH-responsive freshness indicators: A review

Natural pigments are an indicator component in the freshness indicator, which is advantageous due to their safety, renewability, and low cost. However, freshness indicator with natural pigments as pH indicators has the problems of low stability and the color rendering domain could not effectively cover the shelf life of food. This paper describes the types and structures of natural pigments commonly used in freshness indicators and their color change mechanisms under different pH conditions. Also, the preparation methods of natural pigments freshness indicators are reviewed. Based on the current limitations and shortcomings faced by natural pigments freshness indicators, this paper highlights optimization strategies to enhance their sensitivity and stability, including modification, co-pigmentation, natural pigments mixing, encapsulation, and metal-ion complexation. The exploitation of these optimization strategies can help develop natural pigment-based intelligent packaging with superior performance to meet the food industry's needs for quality and safety monitoring.

Multifunctional honeysuckle extract/attapulgite/chitosan composite films containing natural carbon dots for intelligent food packaging

In order to fulfill people's requirements for food quality and safety, it is a promising strategy to develop intelligent biodegradable food packaging materials. Herein, honeysuckle extracts/attapulgite/chitosan composite films containing natural carbon dots were fabricated for intelligent food packaging. Different characterization techniques were employed to study the obtained composite films, while the physicochemical properties, optical properties, antibacterial and antioxidant activities of composite films were determined. The obtained composite films presented good mechanical, antibacterial and antioxidant properties, and the antibacterial ratios of composite films against Escherichia coli and Staphylococcus aureus were 99.27 ± 0.18 % and 98.85 ± 0.65 %, respectively. When the added amount of honeysuckle extracts/attapulgite nanocomposites was 4.76 %, the tensile strength and elongation at break of composite films reached 24.9 ± 2.35 MPa and 64.8 ± 2.11 %, respectively, which were obviously higher than that of pure chitosan film. Furthermore, the composite films exhibited excellent UV shielding and blue fluorescence properties, as well as pH-sensitivity due to the presence of caffeoquinic acid-based natural carbon dots derived from honeysuckle extract. Therefore, the composite films indicated a potential application for intelligent food packaging.

A sensing label or gel loaded with an NIR emission fluorescence probe for ultra-fast detection of volatile amine and fish freshness

A simple benzopyran-based fluorescence probe DCA-Apa detection of volatile amine has been synthesized. DCA-Apa can recognize volatile amines by dual channel mode (changing from blue to light yellow in sunlight, and from weak pink to orange under 365 nm) in pure water system. DCA-Apa has the advantages of ultra-fast response (∼6 s), NIR emission (655 nm), and a good fluorescence response for many amines. The sensing label or gel loaded with DCA-Apa was prepared by the dipping or mixing method using filter paper or gelatin as solid carriers, which can identify volatile amine vapor and monitor the freshness of salmon by colorimetric and fluorescent dual channels. When the color of the label changes to light yellow-green or the fluorescence of the label becomes orange fluorescence (365 nm UV lamp), it indicates that the fish has rotted. The two-channel method makes up for the deficiency of the single colorimetric method, and establishes a theoretical foundation for more precise assessment of fish freshness.

The Use of Novel Colorimetric Films to Monitor the Freshness of Pork, Utilizing Konjac Glucomannan With Curcumin/Alizarin

In this study, different proportions of curcumin (CUR) and alizarin (ALI) were added to konjac glucomannan (KG)/ polyvinyl alcohol (PVA) to prepare an active intelligent packaging film and evaluate its potential to indicate pork freshness. The mixed indicator had a richer color hierarchy in the buffer solution with pH = 2-12. The surface of the KG-2C2A and KG-1C3A films is smoother and has fewer cross-section faults. With the increase of CUR content in the film, the crystal structure becomes more prominent, leading to poor compatibility with KG. The WAC of KG-3C1A and KG-1C3A films was significantly higher than that of the other groups, and they had better hydrophobicity. With the increase of CUR content in the films, the thermal stability of the films was enhanced, and the KG-C films showed the highest thermal stability. Among them, the KG-2A2C and KG-1C3A films showed the most significant color change during pork spoiling and could be used to monitor the freshness of pork. As a pH colorimetric indicator, CUR and ALI-coated KG films might be of great potential in fresh meat monitoring.

Identification, quantification and nutraceutical evaluation of the extracts from Arnebia benthamii roots of Himalayan regions of J&K, India

Arnebia benthamii is one of the important sources of biologically active naphthoquinone pigments. The present study aimed at extraction of shikonin from Arnebia benthamii roots and its characterization. In order to identify and quantify shikonin, the extracts were evaluated using HPLC, LCMS, GCMS, NP-HPTLC and FTIR. Furthermore, nutraceutical evaluation was also done. It was found that the amount of shikonin was very low in the extracts obtained by using aqueous ethanol as it was not detected through chromatographic techniques. However, when hexane was used for extraction, a significant amount of shikonin (4.55 mg/g) was detected. The shikonin showed a linear range from 2-55 µg/mL with LOD and LOQ of 2.65 and 8.02 respectively, with a retention time of 3.64 min. The results of FTIR revealed that hexane extract had the intensity of functional groups similar to that of the standard. The values of DPPH radical inhibition were observed as 82.98 ± 0.01, 65.09 ± 0.23 %, 62.28 ± 0.86 % and 54.09 ± 0.23 % for Std, Ehex, Eus and Evs, respectively. The hexane extract showed the highest antioxidant activity as compared to other samples. Moreover, the hexane extracted shikonin displayed significantly (p > 0.05) high α-amylase and pancreatic lipase inhibition, indicating its high anti-diabetic and anti-lipidemic potential. It can be concluded that hexane is the best solvent for the extraction of shikonin and has better nutraceutical potential compared to ethanolic extracts.

A starch/gelatin-based Halochromic film with black currant anthocyanin and Nanocellulose-stabilized cinnamon essential oil Pickering emulsion: Towards real-time Salmon freshness assessment

Neoterically, food packaging systems designed solely for prolonging shelf life or monitoring freshness could not fulfil the dynamic demands of consumers. In this current investigation, using the solvent casting method, a versatile halochromic indicator was created by integrating black currant anthocyanin and cinnamon essential oil-loaded Pickering emulsion into a starch/gelatin matrix. The resulting indicator film underwent scrutiny for its structural, pH-sensitive, antioxidant, and antimicrobial attributes. Unexpectedly, the amalgamation of anthocyanin and essential oil led to decreased antioxidant activity, dropping from 73.23 ± 2.17 to 28.87 ± 2.50 mg Trolox equivalent/g sample. Additionally, no discernible antimicrobial properties were detected in the composite film sample against both Staphylococcus aureus and Escherichia coli. Fourier transform infrared analyses unveiled robust intermolecular interactions among the film-forming components, providing insights into the observed antagonistic effect. The indicator film displayed distinctive colour changes corresponding to the fresh (greyish-brown), onset of decomposition (khaki), and spoiled (dark green) stages of the stored fish sample. This highlights its promising potential for providing real-time indications of food spoilage. These findings are important for the efficient design of composite films incorporating anthocyanins and essential oils. They serve as a guide towards their potential use as multifunctional packaging materials in the food industry.

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.

Hybrid chiral nanocellulose-cyanidin composite with pH and humidity response for visual inspection and real-time tracking of shrimp quality and freshness

Biobased multi-stimulation materials have received considerable attention for intelligent packaging and anti-counterfeiting applications. Cellulose nanocrystals (CNCs) and cyanidins are good material candidates for monitoring food freshness as they are eco-friendly natural substances. This work incorporated cyanidin with a CNC-hosting substrate to develop a simple, environment-friendly colorimetric device to visualize food freshness. Across the pH range of 2-13, the indicator exhibited noticeable color changes ranging from red to gray and eventually to orange. The CNC-cyanidin (CC) film exhibited a dramatic color change from blue to dark red and high sensitivity at a relative humidity of 30 %-100 %. In corresponding to the total volatile elemental nitrogen (TVB-N) level of shrimp, the indicator showed distinguishable colors at different stages of shrimp. The findings imply that the samples have substantial potential for use as an intelligent indicator for tracking shrimp freshness.

Sodium alginate/ager colourimetric film on porous substrate layer: Potential in intelligent food packaging

Colourimetric indicators have potential applications in monitoring food freshness and offer a simple, rapid, effective, and economical approach. Blending sodium alginate (SA) with agar (AG), an ideal choice for solid substrates in colourimetric indicators, can modify mechanical compliance and optical properties. However, the limitations in the water-sustaining capacity and dye migration of hydrogel substrates significantly impede the scalability and commercial application of these indicators. In this study, we designed and prepared a bilayer-structured indicator featuring an SA/AG colourimetric film on a porous Polypropylene fluoride (PVDF)/SiO2 encapsulation film. This design aims to enhance the water-sustaining capacity and reduce dye migration from the SA/AG colourimetric film. The PVDF/SiO2 composite film was prepared using a peeling-assisted phase-conversion process, which enabled the indicator to selectively allow gas, but not water, to pass through its porous substrate. Furthermore, we tested the layered indicator film by monitoring changes in shrimp freshness. The results revealed significant and distinguishable colour changes in the indicators corresponding to the freshness and spoilage of the shrimp.

Modification and characterization of a novel and fluorine-free cellulose nanofiber with hydrophobic and oleophobic properties

In this study, a brand-new, easy, and environmentally friendly approach for chemically functionalizing 2,2,6,6-tetramethylpiperidinyloxyl radical (TEMPO)-oxidized cellulose nanofiber (TOCNF) to produce modified cellulose nanofiber (octadecylamine-citric acid-CNF) was proposed. Effects of octadecylamine (ODA)/TOCNF mass ratio on the chemical structure, morphology, surface hydrophobicity and oleophobicity were studied. According to Fourier transform infrared spectroscopy (FTIR) analysis, ODA was successfully grafted onto the TOCNF by simple citric acid (CA) esterification and amidation reactions. Scanning electron microscopy (SEM) showed that a new rough structure was formed on the ODA-CA-CNF surface. The water contact angle (WCA) and the castor oil contact angle (OCA) of the ODA-CA-CNF reached 139.6° and 130.6°, respectively. The high-grafting-amount ODA-CA-CNF was sprayed onto paper, and the OCA reached 118.4°, which indicated good oil-resistance performance. The low-grafting-amount ODA-CNF was applied in a pH-responsive indicator film, exhibiting a colour change in response to the pH level, which can be applied in smart food packaging. The ODA-CA-CNF with excellent water/oil-resistance properties and fluorine-free properties can replace petrochemical materials and can be used in the fields of fluorine-free oil-proof paper.

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.

Development of a Sensitive Colorimetric Indicator for Detecting Beef Spoilage in Smart Packaging

This study aimed to fabricate and characterize a novel colorimetric indicator designed to detect ammonia (NH3) and monitor meat freshness. The sensing platform was constructed using electrospun nanofibers made from polylactic acid (PLA), which were then impregnated with anthocyanins as a natural pH-sensitive dye, extracted from red cabbage. This research involved investigating the relationship between the various concentrations of anthocyanins and the colorimetric platform's efficiency when exposed to ammonia vapor. Scanning electron microscope (SEM) results were used to examine the morphology and structure of the nanofiber mats before and after the dip-coating process. The study also delved into the selectivity of the indicator when exposed to various volatile organic compounds (VOCs) and their stability under extreme humidity levels. Furthermore, the platform's sensitivity was evaluated as it encountered ammonia (NH3) in concentrations ranging from 1 to 100 ppm, with varying dye concentrations. The developed indicator demonstrated an exceptional detection limit of 1 ppm of MH3 within just 30 min, making it highly sensitive to subtle changes in gas concentration. The indicator proved effective in assessing meat freshness by detecting spoilage levels in beef over time. It reliably identified spoilage after 10 h and 7 days, corresponding to bacterial growth thresholds (107 CFU/mL), both at room temperature and in refrigerated environments, respectively. With its simple visual detection mechanism, the platform offered a straightforward and user-friendly solution for consumers and industry professionals alike to monitor packaged beef freshness, enhancing food safety and quality assurance.

Biopolymer-based intelligent packaging integrated with natural colourimetric sensors for food safety and sustainability

Increasing concerns about global food safety and security demands innovative solutions, particularly in food packaging technologies. This review paper investigates the advanced integration of natural colourimetric sensors with biopolymer-based packaging materials, with a focus on developments over the past 5 years. These sensors change colour in response to environmental stimuli such as oxygen, temperature, pH and relative humidity, intuitively indicating food freshness and safety. The paper emphasizes the recent advancements in using natural colourants, such as alizarin, anthocyanins, betacyanins, chlorophyll, curcumin and shikonin. When combined with either natural or synthetic biopolymers, these colourants contribute to a sustainable and eco-friendly approach to food packaging. Such technological advances could notably decrease the incidence of foodborne illnesses by signaling potential spoilage or contamination, while also addressing food wastage by providing clear indications of edibility. Although challenges remain in sensor longevity and widespread adoption, the prospects for biopolymer-based food packaging with embedded natural colourimetric sensors are promising.

Response surface methodology to optimize the sterilization process of slightly acidic electrolyzed water for Chinese shrimp (Fenneropenaeus chinensis) and to investigate its effect on shrimp quality

Chinese shrimps are popular among consumers for their delicious taste and high nutritional value, but they are highly susceptible to deterioration due to microbial contamination with degradation of texture, color and flavor. The aim of this study was to evaluate the effects of available chlorine concentration (ACC), processing time and material-liquid ratio on the bacterial inhibition rate of shrimp treated with slightly acidic electrolyzed water (SAEW). The effective parameters were optimized by response surface methodology to the optimal bactericidal conditions: ACC 88 mg/L, processing time 12 min, and material-liquid ratio 1:4. The actual bactericidal inhibition rate of shrimp under these conditions was 37.60 %. On this basis, the quality, color difference and textural changes of shrimp treated with SAEW, sodium hypochlorite and alkaline electrolytic water were compared and investigated during storage at 4 °C. The combined results showed that the SAEW treatment could extend the shelf-life by more than 2 d.

Amine vapor-responsive ratiometric sensing tag based on HPTS/TPB-PVA fluorescent film for visual determination of fish freshness

In this study, amine vapor-sensitive films with ratiometric fluorescence attributes were developed. The pH-sensitive fluorescein 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) and its tetraphenylethylene derivative (TPB) were selected as ratiometric indicators and incorporated into a polyvinyl alcohol (PVA) matrix to produce HPTS/TPB-PVA films. The films responded well to amine vapors, and the interference of aromatic vapors did not substantially affect the fluorescence signals of the films. Under UV light at a wavelength of 365 nm, the fluorescence of the films changed from dark pink to light pink and finally to yellow when the freshness of the fish was visually checked during storage. In addition, the color difference values of the films showed a positive correlation with the total volatile basic nitrogen (TVB-N), ranging from 12.7 to 24.8 mg/100 g at 25 °C and 8.4 to 25.6 mg/100 g at 4 °C, respectively. This indicates that fluorescent films have good potential for quantifying fish freshness in the near future when connected to an automatic data processing system based on color differences.

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.

Inhibition of Biofilm Formation in Cutibacterium acnes, Staphylococcus aureus, and Candida albicans by the Phytopigment Shikonin

Skin microbiota, such as acne-related Cutibacterium acnes, Staphylococcus aureus, and fungal Candida albicans, can form polymicrobial biofilms with greater antimicrobial tolerance to traditional antimicrobial agents and host immune systems. In this study, the phytopigment shikonin was investigated against single-species and multispecies biofilms under aerobic and anaerobic conditions. Minimum inhibitory concentrations of shikonin were 10 µg/mL against C. acnes, S. aureus, and C. albicans, and at 1-5 µg/mL, shikonin efficiently inhibited single biofilm formation and multispecies biofilm development by these three microbes. Shikonin increased porphyrin production in C. acnes, inhibited cell aggregation and hyphal formation by C. albicans, decreased lipase production, and increased hydrophilicity in S. aureus. In addition, shikonin at 5 or 10 µg/mL repressed the transcription of various biofilm-related genes and virulence-related genes in C. acnes and downregulated the gene expression levels of the quorum-sensing agrA and RNAIII, α-hemolysin hla, and nuclease nuc1 in S. aureus, supporting biofilm inhibition. In addition, shikonin prevented multispecies biofilm development on porcine skin, and the antimicrobial efficacy of shikonin was recapitulated in a mouse infection model, in which it promoted skin regeneration. The study shows that shikonin inhibits multispecies biofilm development by acne-related skin microbes and might be useful for controlling bacterial infections.

Development of seaweed-derived polysaccharide/cellulose nanocrystal-based antifogging labels loaded with alizarin for monitoring aquatic products' freshness

Intelligent freshness indicator labels have attracted great interest for their massive potential in monitoring the freshness of aquatic products over the years. However, there is still a challenge where fogging on the labels during dramatic temperature changes affects the reading of freshness. At the same time, the freshness indicator labels need high mechanical strength to resist collision damage during transportation and storage. Herein, an antifogging freshness indicator label was developed based on seaweed extracts and alizarin. Firstly, soluble polysaccharides and insoluble components were extracted from Gelidium amansii, and cellulose nanocrystal (CNC) was further prepared from the insoluble components by sulfuric acid hydrolysis. Subsequently, a polysaccharide-based film was fabricated using soluble polysaccharides as the matrix materials and CNC as the reinforcement agent. Antifogging experiments showed that the hydrophilic composite films presented good antifogging performance. After loading with alizarin, the composite indicator label exhibited both antifogging and freshness-indicating properties for the salmon sample. The work provided a new idea for developing freshness indicator labels suitable for low-temperature transportation and storage.

Novel ammonia-sensitive sodium alginate-based films containing Co-Imd microcrystals for smart packaging application

Currently, there is an urgent requirement for the fabrication of smart packaging materials that can be applied for the real-time visual monitoring of food freshness. In this research, cubic Co-MOF (Co-Imd) microcrystal with ammonia-sensitivity and antibacterial activity was manufactured and then anchored within sodium alginate (NaAlg) matrix to construct smart packaging materials. The structure, physical and functional performances of NaAlg-based films with different content of Co-Imd (0.5, 1.0 and 2.0 wt% on NaAlg basis) were then evaluated in detail. Results reveal that the incorporated Co-Imd fillers are equally anchored within the NaAlg matrix due to the generation of new hydrogen-bonding interaction, which make an obvious improvement in mechanical strength, toughness, oxygen/water barrier, and UV-blocking ability of the NaAlg film. Moreover, the constructed NaAlg/Co-Imd blend films show superior antibacterial capability, ammonia-sensitivity function as well as color stability. Ultimately, the NaAlg/Co-Imd blend films were successfully utilized for indicating the deterioration of shrimp based on noticeable color alteration, suggesting their tremendous prospects for utilization in smart active packaging. This work offers a facile and efficient method for fabricating novel ammonia-sensitive and long-term color-stable NaAlg-based film materials with improved mechanical strength, toughness, oxygen/water barrier, UV-blocking, and antibacterial performances for smart active packaging application.

A Novel Indicator Based on Polyacrylamide Hydrogel and Bromocresol Green for Monitoring the Total Volatile Basic Nitrogen of Fish

An intelligent indicator was developed by immobilizing bromocresol green (BCG) within the polyacrylamide (PAAm) hydrogel matrix to monitor the total volatile basic nitrogen (TVB-N) content of fish. The FTIR analysis indicated that BCG was effectively incorporated into the PAAm through the formation of intermolecular hydrogen bonds. A thermogravimetric analysis (TGA) showed that the PAAm/BCG indicator had a mere 0.0074% acrylamide monomer residue, meanwhile, the addition of BCG improved the thermal stability of the indicator. In vapor tests with various concentrations of trimethylamine, the indicator performed similarly at both 4 °C and 25 °C. The total color difference values (ΔE) exhibited a significant linear response to TVB-N levels ranging from 4.29 to 30.80 mg/100 g at 4 °C (R2 = 0.98). Therefore, the PAAm/BCG indicator demonstrated stable and sensitive color changes based on pH variations and could be employed in smart packaging for real-time assessment of fish freshness.

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.

Recent advances on natural colorants-based intelligent colorimetric food freshness indicators: fabrication, multifunctional applications and optimization strategies

With the increasing concerns of food safety and public health, tremendous efforts have been concentrated on the development of effective, reliable, nondestructive methods to evaluate the freshness level of different kinds of food. Natural colorants-based intelligent colorimetric indicators which are typically constructed with natural colorants and polymer matrices has been regarded as an innovative approach to notify the customers and retailers of the food quality during the storage and transportation procedure in real-time. This review briefly elucidates the mechanism of natural colorants used for intelligent colorimetric indicators and fabrication methodologies of natural colorants-based food freshness indicators. Subsequently, their multifunctional applications in intelligent food packaging systems like antioxidant packaging, antimicrobial packaging, biodegradable packaging, UV-blocking packaging and inkless packaging are well introduced. This paper also summarizes several optimizing strategies for the practical application of this advanced technology from different perspectives. Strategies like adopting a hydrophobic matrix, constructing double-layer film and encapsulation have been developed to improve the stability of the indicators. Co-pigmentation, metal ion complexation, pigment-mixing and using substrates with high surface area are proved to be effective to enhance the sensitivity of the indicators. Approaches include multi-index evaluation, machine learning and smartphone-assisted evaluation have been proven to improve the accuracy of the intelligent food freshness indicators. Finally, future research opportunities and challenges are proposed. Based on the fundamental understanding of natural colorants-based intelligent colorimetric food freshness indicators, and the latest research and findings from literature, this review article will help to develop better, lower cost and more reliable food freshness evaluation technique for modern food industry.

Investigating the microbial properties of sodium alginate/chitosan edible film containing red beetroot anthocyanin extract for smart packaging in chicken fillet as a pH indicator

The current trend in the production of smart films involves the use of pH-responsive color indicators derived from natural sources. In line with this trend, the aim of this research is to produce edible films from sodium alginate (A) and chitosan (Ch) incorporating red beet anthocyanin (Ac) extract, and to assess the properties of these films and their use as coatings for chicken fillets. The study employed a factorial design to evaluate the effects of treatments C (control), A25%-ch75% (films consisting of 25% sodium alginate and 75% chitosan), and A25%-ch75%-Ac (films consisting of 25% sodium alginate, 75% chitosan, and red beet anthocyanin). The findings indicate that the inclusion of red beet anthocyanin extract did not result in any discernible differences in the FTIR spectra of the film samples. Analysis of the XRD results revealed that the addition of the extract led to a reduction in the crystal structure of the film. Moreover, SEM results demonstrated that the extract caused alterations in the polymer chains and an increase in the porosity of the film matrix. With regard to the chicken fillet samples coated with the film, over time, there was an increase in microbial analysis (total microorganism count and Staphylococcus aureus coagulase-positive) and chemical properties (pH, peroxide, thiobarbituric acid, and nitrogen compounds) for all samples. However, this trend was significantly lower in the samples coated with the Ac extract (P < 0.05). Texture analysis results revealed that the hardness parameter of all samples decreased over the storage period, while the samples containing the Ac extract demonstrated a significant increase in this parameter (P < 0.05). Additionally, the color changes of the pH sensor corresponded to the anthocyanin structure. Based on the results, the smart film composed of sodium alginate/chitosan incorporating red beet anthocyanin extract has the potential to enhance the quality, prolong the shelf life, and decrease the microbial load of chicken fillet when used as a coating. Furthermore, red beet anthocyanin can serve as a suitable indicator for spoilage changes in packaged food products.

pH-sensitive smart indicators based on cellulose and different natural pigments for tracing kimchi ripening stages

Five natural pigments including water-soluble [butterfly pea (BP), red cabbage (RC), and aronia (AR)] and alcohol-soluble [shikonin (SK) and alizarin (ALZ)] were extracted, characterized, and loaded onto cellulose for preparing pH-sensitive indicators. The indicators were tested their color response efficiency, gas sensitivity, response to lactic acid, color release, and antioxidant activity. Cellulose-water soluble indicators showed more obvious color changes than alcohol-soluble indicators in lactic acid solution and pH solutions (1-13). All cellulose-pigment indicators exhibited prominent sensitivity to ammonia compared to acidic vapor. Antioxidant activity and release behavior of the indicators were influenced by pigment type and simulants. Kimchi packaging test was carried out using original and alkalized indicators. The alkalized indicators were more effective in showing visible color changes during kimchi storage than the original indicators, and cellulose-ALZ displayed the most distinct color change from violet (fresh kimchi, pH 5.6, acidity 0.45 %) to gray (optimum fermented kimchi, pH 4.7, acidity 0.72 %), and to yellow (over fermented kimchi, pH 3.8, acidity 1.38 %) which followed by BP, AR, RC, SK respectively. The findings of the study suggest that the alkalization method could be used to show noticeable color changes in a narrow pH range for application with acidic foods.

Sumac (Rhus coriaria L.) anthocyanin loaded-pectin and chitosan nanofiber matrices for real-time monitoring of shrimp freshness

In this study, pectin (PC)/chitosan nanofiber (ChNF) films containing a novel anthocyanin from sumac extract were successfully developed for freshness monitoring and shelf-life extension of shrimp. The physical, barrier, morphological, color, and antibacterial properties of biodegradable films were evaluated. The addition of sumac anthocyanins to the films caused intramolecular interactions (such as hydrogen bonds) in the film structure, as confirmed by using attenuated total reflectance Fourier transform infrared (ATR-FTIR) analysis, suggesting good compatibility of film ingredients. Also, intelligent films showed significant sensitivity to ammonia vapors and changed color from reddish to olive color at the first 5 min. Moreover, the results showed that PC/ChNF and PC/ChNF/sumac films have significant antibacterial activity against Gram-positive bacteria and Gram-negative bacteria. In addition to the good functional characteristics of the smart film, the resulting films showed acceptable physicomechanical properties. So, PC/ChNF/sumac smart film exhibited the strength = 60 MPa with the flexibility = 23.3 %. Likewise, water vapor barrier reduced from 2.5 (×10^-11 g. m/m². s. Pa) to 2.3 (×10^-11 g. m/m². s. Pa) after adding anthocyanin. The results of the application of intelligent film containing anthocyanins of sumac extract for shrimp freshness monitoring showed that the color of the intelligent film changed from reddish to greenish color after 48 h of storage, which shows the high potential of the produced film for monitoring the spoilage of seafood products.

Cellulose nanofiber-based multifunctional films integrated with carbon dots and anthocyanins from Brassica oleracea for active and intelligent food packaging applications

A new generation of carbon dot-based active and intelligent packaging films with UV blocking, antibacterial, and real-time sensing potentials was fabricated using Brassica oleracea (BO) extract. The cellulose nanofiber (CNF) was used to prepare the multifunctional intelligent nanocomposite film integrated with BO anthocyanins (BOA) and BO-biowaste-derived carbon dots (BO-CDs). The incorporation of 1.5 % BO-CD and 6 % BOA in the CNF matrix improved the physicochemical and UV blocking (>189 % increase) properties of the fabricated films. The synthesized BO-CD exhibits high fluorescence, UV absorption, antibacterial and antioxidant functions. It showed strong radical scavenging activity against ABTS (~90 %) and DPPH (~80 %) compared to the neat CNF film. Scanning electron microscopy and X-ray photoelectron spectroscopy (XPS) have shown enhanced compatibility and elemental composition of the BO-CDs/BOA additives in the CNF-polymer matrix. Packaging tests showed that the prepared film worked efficiently and non-destructively and was able to monitor the freshness of minced pork, fish, and shrimp in real-time through a distinct visual change from red to colorless/yellow during storage at 25 °C for 48 h. Active and intelligent films developed based on CNF/BO-CDs/BOA are expected to be applied as multifunctional packaging materials that can indicate quality changes and extend the shelf life of packaged perishable foods.

Application of smart packaging for seafood: A comprehensive review

Nowadays, due to the changes in lifestyle and great interest of consumers in a healthy life, people have started increasing their seafood consumption. But due to their short shelf life, experts are looking for a new packaging called smart packaging (SMP) for seafood. There are different indicators/sensors in SMP; one of the effective indices is time-temperature, which can show consumers the best time of using seafood based on their shelf life and experienced temperature. Another one is radio-frequency identification (RFID) that is a transmission device that represents a separate form of the electronic information-based SMP systems. RFID does not belong to any of the categories of markers or sensors; it is an auto recognition system that applies cordless sensors to indicate segments and collect real-time information without manual interposition. This review covers the use of SMP in all marine foods, including fish, due to its high consumption and high content of polyunsaturated fatty acids, eicosapentaenoic acid (C20:5n-3) and docosahexaenoic acid (C22:6n-3), which are the considerable factors of n-3 polyunsaturated fatty acids for human.

Innovative processes in smart packaging. A systematic review

Smart packaging provides one possible solution that could reduce greenhouse gas emissions. In comparison with traditional packaging, which aims to extend the product's useful life and to facilitate transport and marketing, smart packaging allows increased efficiency, for example by ensuring authenticity and traceability from the product's origin, preventing fraud and theft, and improving security. Consequently, it may help to reduce pollution, food losses, and waste associated with the food supply chain. However, some questions must be answered to fully understand the advantages and limitations of its use. What are the most suitable smart packaging technologies for use in agro-industrial subsectors such as meat, dairy, fruits, and vegetables, bakery, and pastry? What are the opportunities from a perspective of life extension, process optimization, traceability, product quality, and safety? What are the future challenges? An up-to-date, systematic review was conducted of literature relevant to the application of indicator technologies, sensors, and data carriers in smart packaging, to answer these questions. © 2022 Society of Chemical Industry.

Improving shikonin solubility and stability by encapsulation in natural surfactant-coated shikonin nanoparticles

It is significant to develop a colloidal delivery system to improve the water solubility, stability, and bioavailability of shikonin, which is a hydrophobic plant polyphenol with a variety of physiological activities. In this study, three kinds of natural surfactants (saponin, sophorolipid, and rhamnolipid) were used to prepare shikonin nanoparticles by the pH-driven method. The physicochemical and structural properties of the shikonin nanoparticles were characterized, including particle size, zeta potential, and morphology. The encapsulation efficiencies of shikonin nanoparticles coated with saponin and sophorolipid were 97.6% and 97.3%, respectively, which were much higher than that of rhamnolipid-coated shikonin nanoparticles (19.0%). Shikonin nanoparticles coated with saponin and sophorolipid showed good resistance to heat and light and maintained long-term stability during storage. Moreover, shikonin nanoparticles coated with saponin and sophorolipid improved their in vitro-bioavailability. PRACTICAL APPLICATION: These article results are of great importance for improving the stability and bioavailability of shikonin in functional foods, dietary supplements, or pharmaceutical preparations. Moreover, this study provided theoretical and practical guides for further research of shikonin nanoparticles and may promote the development of natural colloidal delivery systems.

Edible pH sensitive polysaccharide-anthocyanin complex films for meat freshness monitoring

One of the innovative methods for real-time determination of food freshness is the application of pH-indicator sensors, where the color change can be used for the visual detection of acidic/basic volatile compounds formed during product storage due to microbial growth. The aim of the present study is to develop a pH-responsive freshness indicator based on anthocyanins from chokeberry (Aronia melanocarpa Elliot) and black carrot (Daucus carota ssp. sativus var. atrorubens Alef.), incorporated into an alginate/pectin/arabic gum composite film. The resulting films show distinct color changes as the pH varies. The color changes from red (pH 2.0 - 3.0) through pink and pale pink (pH 4.0, 5.0 and 6.0) to purple and blue (pH 7.0 - 8.0). The most distinct is the color transition between pH 6.0 and 7.0 for the black carrot extract and the chokeberry: black carrot mixture (1:3). The applicability of the developed pH-indicator films was demonstrated in chicken meat by tracking the changes during its storage at 4°C for 7 d. The observed results show a distinct color change from pink (day 1-3) to violet and blue on day 7. The developed pH- sensitive films have potential for use in a smart packaging system as a sensor for meat freshness monitoring.

Nanosized Shikonin-Fe(III) Coordination Material for Synergistic Wound Treatment: An Initial Explorative Study

Shikonin (Shik), a natural pigment, has received growing interest in various biomedical fields due to its anti-inflammatory, antitumor, antimicrobial, and antioxidant ability. However, some inherent characteristics of Shik, such as its virulence, low bioavailability, and poor solubility, have limited its biomedical applicability. Here, we reported a facile synthetic method to produce the Shik-iron (III) nanoparticles (Shik-Fe NPs), which could overcome these limitations of Shik. The synthesized Shik-Fe NPs possessed a uniform size range of 110 ± 10 nm, negative surface charges, good water dispersity, and high safety. Iron distributed uniformly inside Shik-Fe NPs, and iron constituted 20% of total mass in PEGylated Shik-Fe NPs. When interacting with activated macrophages, Shik-Fe NPs significantly reduced the level of cellular inflammatory factors, for example, iNOS, IL-1β, and TNF-α. Furthermore, the Shik-Fe NPs demonstrated synergistic anti-inflammation and anti-bacterial properties in vivo, since they could release Fe³⁺ and Shik to eradicate bacteria (Staphylococcus aureus and P. aeruginosa were used as model microbes here) during wound infections and provide full recovery for scald wounds. Collectively, the study established a dual-functional Shik-derived nanoplatform, which could be useful for the treatment of various inflammation-involved diseases.

Carboxymethyl Cellulose/Gelatin Hydrogel Films Loaded with Zinc Oxide Nanoparticles for Sustainable Food Packaging Applications

The current research work presented the synthesis of carboxymethyl cellulose-gelatin (CMC/GEL) blend and CMC/GEL/ZnO-Nps hydrogel films which were characterized by FT-IR and XRD, and applied to antibacterial and antioxidant activities for food preservation as well as for biomedical applications. ZnO-Nps were incorporated into the carboxymethyl cellulose (CMC) and gelatin (GEL) film-forming solution by solution casting followed by sonication. Homogenous mixing of ZnO-Nps with CMC/GEL blend improved thermal stability, mechanical properties, and moisture content of the neat CMC/GEL films. Further, a significant improvement was observed in the antibacterial activity and antioxidant properties of CMC/GEL/ZnO films against two food pathogens, Staphylococcus aureus and Escherichia coli. Overall, CMC/GEL/ZnO films are eco-friendly and can be applied in sustainable food packaging materials.

Preparation and application of a colorimetric film based on sodium alginate/sodium carboxymethyl cellulose incorporated with rose anthocyanins

To monitor the freshness of Penaeus vannamei during storage, a colorimetric film based on sodium alginate/sodium carboxymethyl cellulose incorporated with rose anthocyanins extract (RAE) was prepared. The results showed that the incorporation of RAE increased moisture content, water vapor permeability, and water contact angle of the colorimetric film. FTIR, XRD spectra, and SEM demonstrated that RAE had good compatibility with the film-forming substrate. The colorimetric film presented obvious color variation in the pH range of 2.0-12.0 and was sensitive to volatile ammonia. The colorimetric film exhibited a visual color change from pink to pale yellow to yellowish green during the storage of Penaeus vannamei at 4 °C. Significant correlations were observed between the color change of colorimetric film (ΔE) and the pH value or TVB-N content of Penaeus vannamei (p < 0.05). Therefore, the colorimetric film shows great application potential to monitor the freshness of shrimp as intelligent packaging.

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.

Shikonin Functionalized Packaging Film for Monitoring the Freshness of Shrimp

A shikonin embedded smart and active food packaging film was produced using a binary mixture of gelatin and cellulose nanofiber (CNF). Shikonin is an alcohol-soluble natural pigment extracted from Lithospermum erythrorhizon root. The fabricated film showed good pH-responsive color changes and volatile gas sensing properties. Moreover, the film exhibited excellent antioxidant and antibacterial activity against foodborne pathogens. The shikonin incorporated gelatin/CNF-based film showed excellent UV-light barrier properties (>95%) and high tensile strength (>80 MPa), which is useful for food packaging. The hydrodynamic properties of the film were also slightly changed in the presence of shikonin, but the thermal stability and water vapor permeability remained unaffected. Thus, the inclusion of shikonin in the gelatin/CNF-based film improves not only the physical properties but also the functional properties. The film’s color indicator properties also clearly show shrimp’s freshness and spoilage during storage for 48 h. The shikonin-based functional film is expected to be a promising tool for multi-purpose smart and active food packaging applications.

Design and Preparation of a Biobased Colorimetric pH Indicator from Cellulose and Pigments of Bacterial Origin, for Potential Application as Smart Food Packaging

Nowadays, worldwide challenges such as global warming, pollution, unsustainable consumption patterns, and scarcity of natural resources are key drivers toward future-oriented bioeconomy strategies, which rely on renewable biobased resources, such as bacterial pigments and bacterial cellulose (BC), for materials production. Therefore, the purpose of this study was to functionalize bacterial cellulose with violacein, flexirubin-type pigment, and prodigiosin and test their suitability as pH indicators, due to the pigments’ sensitivity to pH alterations. The screening of the most suitable conditions to obtain the BC-pigment indicators was achieved using a full factorial design, for a more sustainable functionalization process. Then, the pH response of functionalized BC to buffer solutions was assessed, with color changes at acidic pH (BC-violacein indicator) and at alkaline pH (BC-violacein, BC-prodigiosin, and BC-flexirubin-type pigment indicators). Moreover, the indicators also revealed sensitivity to acid and base vapors. Furthermore, leaching evaluation of the produced indicators showed higher suitability for aqueous foods. Additionally, color stability of the functionalized BC indicators was carried out, after light exposure and storage at 4 °C, to evaluate the indicators’ capacity to maintain color/sensitivity. Thus, BC membranes functionalized with bacterial pigments have the potential to be further developed and used as pH indicators.

Development of gelatin/PVA based colorimetric films with a wide pH sensing range winery solid by-product (Vinasse) for monitor shrimp freshness

Anthocyanins were extracted from a winery solid by-product (Vinasse) and added to fish gelatin (FG) and polyvinyl alcohol (PVA) matrices to create freshness monitoring labels. Three different colorimetric indicator smart films [PWE = polyvinyl alcohol with wine extract (WE), FWE = fish gelatin with WE, and PFWE = polyvinyl alcohol and FG blended film with WE] were generated and examined for their suitability to monitor the freshness of shrimp. The mechanical and optical properties, ammonia sensitivity, and colorimetric analysis of smart films were determined. Fourier transform-infrared spectroscopy (FTIR) was used to evaluate the interaction of anthocyanins with FG and PVA and changes in the film's chemical composition with storage. The film surfaces were characterized with atomic force microscopy (AFM). The incorporation of WE enhanced the films' flexibility by providing plasticizer and surfactant properties. The PWE film showed the best color stability. The FWE film showed the least amount of total color change with exposure to ammonia gas and was deemed suitable for refrigerated food packaging. The color of all indicator films showed significant changes suggesting that PWE, FWE, and PFWE films can be utilized in the intelligent packaging application for protein-rich foods to detect spoilage.

RhB@MOF-5 Composite Film as a Fluorescence Sensor for Detection of Chilled Pork Freshness

This study presents a novel composite thin film based on rhodamine B encapsulated into MOF-5 (Metal Organic Frameworks) as a fluorescence sensor for the real-time detection of the freshness of chilled pork. The composite film can adsorb and respond to the volatile amines produced by the quality deterioration of pork during storage at 4 °C, with the fluorescence intensity of RhB decreasing over time. The quantitative model used for predicting the freshness indicator (total volatile base nitrogen) of pork was built using the fluorescence spectra (excited at 340 nm) of the RhB@MOF-5 composite film combined with the partial least squares (PLS) algorithm, providing R_c² and R_p² values of 0.908 and 0.821 and RMSEC (root mean square error of calibration) and RMSEP (root mean square error of prediction) values of 3.435 mg/100 g and 3.647 mg/100 g, respectively. The qualitative model established by the partial least squares discriminant analysis (PLS-DA) algorithm was able to accurately classify pork samples as fresh, acceptable or spoiled, and the accuracy was 86.67%.

Cost-Effective and Portable Instrumentation to Enable Accurate pH Measurements for Global Industry 4.0 and Vertical Farming Applications

Global Vertical Farming (VF) applications with characteristic Industry 4.0 connectivity will become more and more relevant as the challenges of food supply continue to increase worldwide. In this work, a cost-effective and portable instrument that enables accurate pH measurements for VF applications is presented. We demonstrate that by performing a well-designed calibration of the sensor, a near Nernstian response, 57.56 [mV/pH], ensues. The system is compared to a ten-fold more expensive laboratory gold standard, and is shown to be accurate in determining the pH of substances in the 2–14 range. The instrument yields precise pH results with an average absolute deviation of 0.06 pH units and a standard deviation of 0.03 pH units. The performance of the instrument is ADC-limited, with a minimum detectable value of 0.028 pH units, and a typical absolute accuracy of ±0.062 pH units. By meticulously designing bias and amplification circuitry of the signal conditioning stage, and by optimizing the signal acquisition section of the instrument, a (minimum) four-fold improvement in performance is expected.

Smart films fabricated from natural pigments for measurement of total volatile basic nitrogen (TVB-N) content of meat for freshness evaluation: A systematic review

Major databases were searched from January 2012 to August 2021 and 54 eligible studies were included in the meta-analysis to estimate the overall mean of total volatile basic nitrogen (TVB-N) in meat. The mean of TVB-N was 24.96 mg/100 g (95 % CI:23.10-26.82). The pooled estimate of naphthoquinone, curcumin, anthocyanins, alizarin and betalains were 25.98 mg/100 g (95 %CI:19.63-32.33), 30.03 mg/100 g (95 %CI: 24.15-35.91), 24.92 mg/100 g (95 %CI: 22.55-27.30), 23.37 mg/100 g (95 %CI:19.42-27.33) and 19.50 mg/100 g (95 %CI:17.87-21.12), respectively. Meanwhile, subgroups based on meat types showed that smart film was most used in aquatic products at 27.19 mg/100 g (95 %CI:24.97-29.42), followed by red meat at 19.69 mg/100 g (95 %CI:17.44-21.94). Furthermore, 4 °C was the most storage temperature used for testing the performance of smart films at 25.48 mg/100 g (95 %CI:23.05-27.90), followed by storage at 25 °C of 25.65 mg/100 g (95 %CI:22.17-29.13). Substantial heterogeneity was found across the eligible studies (I² = 99 %, p = 0.00). The results of the trim-and-fill method demonstrated publication bias was well controlled.