This research introduces a biodegradable smart packaging film designed for real-time freshness monitoring of shrimp,incorporating zinc oxide nanoparticles(ZnO NPs)and anthocyanin extracted from Hibiscus rosa-sinensis ...This research introduces a biodegradable smart packaging film designed for real-time freshness monitoring of shrimp,incorporating zinc oxide nanoparticles(ZnO NPs)and anthocyanin extracted from Hibiscus rosa-sinensis L.as a pH-responsive indicator.The film matrix,composed of cassava starch,chitosan,and glycerin,was reinforced with varying concentrations of ZnO(0%,6%,and 10%).Structural characterization via X-ray diffraction(XRD)and Fourier-transform infrared spectroscopy(FTIR)confirmed the successful incorporation of ZnO into the biopolymer matrix.Notably,the film containing 6%ZnO exhibited the highest crystallinity index(12.23%)compared to the control(10.29%)and the 10%ZnO variant(10.81%).Mechanical property assessments indicated that the 6%ZnO film demonstrated superior tensile strength(0.78 MPa)and Young’s modulus(2.84 MPa).However,increasing the ZnO content resulted in a decrease in elongation at break,from 41.52%in the control to 27.65%in the 10%ZnO film.Water interaction analyses revealed improved water resistance with ZnO incorporation,as evidenced by a reduction in water solubility from 38.12%(control)to 28.45%(10%ZnO).Biodegradation assays showed a slower degradation rate in ZnO-reinforced films(56.42%for 6%ZnO and 49.87%for 10%ZnO)compared to the control(68.15%)over 15 days,likely attributable to the hydrophobic nature of ZnO nanoparticles.Functionally,the film demonstrated effective spoilage detection through visible colorimetric transitions,shifting from reddish-purple to bluish-green within 24 h of shrimp storage,corresponding to pH changes associated with degradation.Overall,the findings underscore the potential of ZnO-reinforced,starch-based films as eco-friendly and smart packaging materials for enhancing food safety and quality monitoring.展开更多
RFID in healthcare is growing rapidly to become a $2.1 billion global business in 2016. Smart packaging for healthcare has additional value, for example in patient compliance recording blister packs that electronicall...RFID in healthcare is growing rapidly to become a $2.1 billion global business in 2016. Smart packaging for healthcare has additional value, for example in patient compliance recording blister packs that electronically record when each pill is taken - or more strictly when it is removed from the pack. Aardex has a different version where the plastic bottle of pills is continuously weighed by a load cell in the base. Thus recording when a pill is removed. These pack-展开更多
Biobased smart packaging is been the most interesting research field.In this study,pH-sensitive films based on anthocyanin molecules from red cabbage and sepiolite mineral nano-clay as functional additives were studie...Biobased smart packaging is been the most interesting research field.In this study,pH-sensitive films based on anthocyanin molecules from red cabbage and sepiolite mineral nano-clay as functional additives were studied.The films were fabricated by casting method of blend polymer Chitosan/Poly(Vinyl Alcohol)at two fillers loading(5wt.%and 10wt.%).The structural,morphological,thermal,optical,hygroscopic,and mechanical properties as well as the pH sensitivity of films were investigated.The thermal properties confirm that the amount of the anthocyanin in sepiolite was around 6.4%.The tensile strength and the young’s modulus of produced composites at 10wt.%sepiolite–anthocyanin content was increased to 8.90 MPa and 163 MPa,respectively.The maximum water absorption that the films may absorb was 12.3%.pH sensitivity analysis showed that the Smart films change the color by changing the pH level,from pink at pH lower than 6 to yellow at pH higher than 6.Thus,the developed pH-sensitive films show band gaps in visible light that make them useful for monitoring milk spoilage.展开更多
In this study,chitin microcapsules were synthesized via the sol-gel method and subsequently functionalized through the encapsulation of curcumin and alizarin.These microcapsules were then incorporated into a polybutyl...In this study,chitin microcapsules were synthesized via the sol-gel method and subsequently functionalized through the encapsulation of curcumin and alizarin.These microcapsules were then incorporated into a polybutylene terephthalate adipate(PBAT)matrix at varying ratios to fabricate active smart packaging membranes.Microscopic morphology(SEM)analysis revealed that the microcapsules exhibited an ovoid morphology.X-ray diffraction spectroscopy(XRD)and Fourier Transform Infrared Spectrometer(FTIR)analyses showed that curcumin/alizarin does not alter the crystal structure of the microcapsules and that there are hydrogen bonding interactions with the microcapsules.To enhance antimicrobial performance,zinc oxide nanoparticles(5 wt%)were introduced into the composite film.Notably,the composite film with a microencapsulation content of 3 wt%exhibited an inhibition rate of 95.7%and 98.3%against E.coli and S.aureus,respectively.Finally,the composite films were assessed for their ability to monitor shrimp freshness.The results indicated that the films not only extended the shelf life of shrimp but also functioned as an effective freshness indicator by signaling spoilage.展开更多
Using biodegradable films as smart packaging to monitor the freshness of meat in real time is a promising and challenging work.Herein,the phosphorus-doped carbon dots(P-CDs)with pH sensitivity were coated on starch/po...Using biodegradable films as smart packaging to monitor the freshness of meat in real time is a promising and challenging work.Herein,the phosphorus-doped carbon dots(P-CDs)with pH sensitivity were coated on starch/polyvinyl alcohol film(SP film)by a simple scrape-coating method and applied to monitor the freshness of pork.The P-CDs@SP film exhibits a uniform surface,excellent mechanical properties,higher light blocking.When the total volatile base nitrogen(TVB-N)of pork exceeded 15 mg/100 g,the color of the film changed from brownish-yellow to purple-red,and the total color difference(ΔE)of the film obviously increased from 10.24 to 9.37 to 20.75 and 22.93 under the storage conditions of 25 and 4℃,respectively.This can be attributed to the abundant hydroxyl groups on the surface of P-CDs and SP film to promote their stable binding through hydrogen bonds,which greatly improves the hydrophilicity of the films,providing conditions for the rapid conversion of the TVB-N to ammonia and the formation of an alkaline environment.This work can simply and effectively monitor the freshness of pork through the changes of film color,will provide a new idea for the preparation of biodegradable smart packaging materials.展开更多
Ideally,packaging materials should ensure the safety and quality of foods,without contributing to environmental degradation.Consequently,there is interest in the development of biodegradable films assembled from natur...Ideally,packaging materials should ensure the safety and quality of foods,without contributing to environmental degradation.Consequently,there is interest in the development of biodegradable films assembled from natural materials,such as polysaccharides,proteins,lipids,and their mixtures.In this review,the physicochemical attributes and functional characteristics of biodegradable films prepared from these food-grade natural substances are summarized.Recent advances in the production of active and intelligent packaging materials are also discussed.Active packaging is designed to improve the shelf life of packaged foods by including antimicrobials or antioxidants,such as essential oils.Intelligent packaging is designed to provide real-time information about the quality,freshness,or safety of packaged foods by including indicators in the film that are responsive to changes in storage conditions,gas levels,pH,etc.Potential applications of intelligent and active packaging materials to fruit,vegetable,meat,seafood,and dairy products are discussed.展开更多
The utilization of natural preservatives and active packaging in extending the shelf life of food products during storage is vital to meet consumer demand for minimally processed food under sustainable systems.Fiber a...The utilization of natural preservatives and active packaging in extending the shelf life of food products during storage is vital to meet consumer demand for minimally processed food under sustainable systems.Fiber and nanofiber,isolated from cells of different biologically active plants,possess antimicrobial activity and can be used as packaging material with an active ingredient.Soluble or insoluble fibers incorporated into edible films or coatings are particularly popular as functional food additives because of their characteristics.Moreover,fiber serves as an excellent packaging material with mechanical strength,antimicrobial properties,water vapor and oxygen permeability,high phenolic content,and thermal stability and therefore can be enhanced by the incorporation of different ingredients,which is also discussed in this work.It has been found that fiber and nanofiber based edible packaging materials can inhibit the growth of pathogenic bacteria and lipid oxidation.Furthermore,substantial changes have been reported in the surface morphology and mechanical properties of films/coatings with the addition of fiber based active materials like beta-glucan,pectin,guar gum,inulin,psyllium,cellulose,hemicellulose,chitosan and lignin.Hence,the existing literature articulates recent developments and their applications.Therefore,fiber/nanofiber can be a promising substitute for synthetic preservatives.展开更多
Phycoerythrin(PE)extract from red algae Laver(Pyropia dentata)was used in the fabrication of a smart pack-aging film.The PE showed pH sensitivity,implying unique color shifts at different pH.The film colors altered fr...Phycoerythrin(PE)extract from red algae Laver(Pyropia dentata)was used in the fabrication of a smart pack-aging film.The PE showed pH sensitivity,implying unique color shifts at different pH.The film colors altered from red through purple-brown to colorless with increasing pH.The smart packaging films were prepared by casting method composed of gelatin(GE),sodium alginate(SA),and cellulose nanofibrils(CNF).The films were coded as GE/SA(control),GE/SA/PE,and GE/SA/CNF/PE.The thickness of the films ranged from 0.24±0.02 mm to 0.33±0.01 mm.The mechanical properties tensile strength(TS)(12.24±0.30 MPa to 17.65±0.33 MPa)and elongation at break(EAB)(79.34%±1.02%-93.36%±0.69%)significantly increased after addition of CNF.The synthesized films showed water contact angle ranged from 84.55±2.12 to 69.41±1.21,suggesting that films were hydrophobic.The Fourier transform infrared spectroscopy(FTIR)and X-ray diffraction(XRD)analysis demonstrated strong interaction among PE,CNF,and biopolymers.The film with GE/SA/CNF/PE exhibited higher thermal stability compared with control film.Then,the films were applied for checking real time application for the freshness of salmon fish.The significant color change of the film occurred and the number of bacterial colony and TVB-N were increased from 3.81 Log CFU/g to 6.94 Log CFU/g and from 4.78 mg/100 g to 32.27 mg/100 g after incubation for 48 h.Therefore,the film with PE and CNF was intended as an excellent candidate for smart packaging film.展开更多
Freshness indicating labels embedded with pH-sensitive anthocyanins are one type of smart packaging tech-nology.However,the application of freshness indicating labels is mainly restricted by the high cost and hy-droph...Freshness indicating labels embedded with pH-sensitive anthocyanins are one type of smart packaging tech-nology.However,the application of freshness indicating labels is mainly restricted by the high cost and hy-drophilicity of the labels.In order to reduce the manufacturing cost,passion fruit(Passiflora edulis)peel powder rich in dietary fibers and anthocyanins was used to prepare freshness indicating labels in this study.Moreover,the prepared labels were further soaked in 0.01,0.05 and 0.1 mol/L of stearic acid ethanol solution to increase the hydrophobicity of the labels.Structural characterization results showed the surface of the labels was covered by self-assembled stearic acid crystals.Stearic acid treatment significantly decreased the moisture content(16.90%→10.92%),hydrophilicity(water contact angle of 40.36°→103.01°),water vapor permeability(18.68×10^(-11) g m^(-1) s^(-1) Pa^(-1)→8.10×10^(-11) g m^(-1) s^(-1) Pa^(-1))and water uptake ability of the labels,which effectively prevented the leak of anthocyanins from the labels.In addition,stearic acid treatment greatly elevated the inner compactness of the films,resulting in improved tensile strength(3.12 MPa→6.18 MPa)and thermal stability.Moreover,stearic acid treatment well maintained the pH-dependent color changeable ability of the labels.The labels changed from reddish brown to olive and brown in the application of shrimp freshness indicating.When the labels were buried in natural soil at 20℃ for 10 days,82.74%-98.83%of the labels could be degraded.Therefore,this study provides a new and facile way to prepare freshness indicating labels.展开更多
Smart packaging with colorimetric pH indicators is vital for food quality monitoring.However,synthetic pH-sensitive dyes pose safety hazards,and conventional methods to fabricate pH-sensitive films lack real-time dete...Smart packaging with colorimetric pH indicators is vital for food quality monitoring.However,synthetic pH-sensitive dyes pose safety hazards,and conventional methods to fabricate pH-sensitive films lack real-time detection.In this study,blueberry anthocyanin(Ant)and petunia dye(PD)were chosen among six natural dyes due to their enhanced pH responsiveness.They were utilized as chromogenic agents,while petunia dye composite film(PDCF)and anthocyanin composite film(AntCF)were synthesized using electrostatic spinning that incorporated natural dye,chitosan(CS),trehalose(TRE),and polyvinyl alcohol(PVA).Finally,a“sandwich”structure pH indicator was created by overlaying two layers of PET on the top and bottom of the composite film and perforating one side.The pH indicator based on PD composite film(PDCF-s)demonstrated superior effectiveness and stability compared to the Ant composite film(AntCF-s)in monitoring pork freshness.The indicators exhibited excellent sensitivity to low concentrations of ammonia vapor,completing the reaction within 2 min.As the pork spoiled,the color of PDCF-s changed visibly from pink to purple,with anΔE value of 40.Moreover,theΔE variation remained stable across different conditions.This study innovatively designed“sandwich”pH indicators,providing a promising natural safe dye for smart packaging,and promoting the use of pH-responsive indicators.展开更多
文摘This research introduces a biodegradable smart packaging film designed for real-time freshness monitoring of shrimp,incorporating zinc oxide nanoparticles(ZnO NPs)and anthocyanin extracted from Hibiscus rosa-sinensis L.as a pH-responsive indicator.The film matrix,composed of cassava starch,chitosan,and glycerin,was reinforced with varying concentrations of ZnO(0%,6%,and 10%).Structural characterization via X-ray diffraction(XRD)and Fourier-transform infrared spectroscopy(FTIR)confirmed the successful incorporation of ZnO into the biopolymer matrix.Notably,the film containing 6%ZnO exhibited the highest crystallinity index(12.23%)compared to the control(10.29%)and the 10%ZnO variant(10.81%).Mechanical property assessments indicated that the 6%ZnO film demonstrated superior tensile strength(0.78 MPa)and Young’s modulus(2.84 MPa).However,increasing the ZnO content resulted in a decrease in elongation at break,from 41.52%in the control to 27.65%in the 10%ZnO film.Water interaction analyses revealed improved water resistance with ZnO incorporation,as evidenced by a reduction in water solubility from 38.12%(control)to 28.45%(10%ZnO).Biodegradation assays showed a slower degradation rate in ZnO-reinforced films(56.42%for 6%ZnO and 49.87%for 10%ZnO)compared to the control(68.15%)over 15 days,likely attributable to the hydrophobic nature of ZnO nanoparticles.Functionally,the film demonstrated effective spoilage detection through visible colorimetric transitions,shifting from reddish-purple to bluish-green within 24 h of shrimp storage,corresponding to pH changes associated with degradation.Overall,the findings underscore the potential of ZnO-reinforced,starch-based films as eco-friendly and smart packaging materials for enhancing food safety and quality monitoring.
文摘RFID in healthcare is growing rapidly to become a $2.1 billion global business in 2016. Smart packaging for healthcare has additional value, for example in patient compliance recording blister packs that electronically record when each pill is taken - or more strictly when it is removed from the pack. Aardex has a different version where the plastic bottle of pills is continuously weighed by a load cell in the base. Thus recording when a pill is removed. These pack-
文摘Biobased smart packaging is been the most interesting research field.In this study,pH-sensitive films based on anthocyanin molecules from red cabbage and sepiolite mineral nano-clay as functional additives were studied.The films were fabricated by casting method of blend polymer Chitosan/Poly(Vinyl Alcohol)at two fillers loading(5wt.%and 10wt.%).The structural,morphological,thermal,optical,hygroscopic,and mechanical properties as well as the pH sensitivity of films were investigated.The thermal properties confirm that the amount of the anthocyanin in sepiolite was around 6.4%.The tensile strength and the young’s modulus of produced composites at 10wt.%sepiolite–anthocyanin content was increased to 8.90 MPa and 163 MPa,respectively.The maximum water absorption that the films may absorb was 12.3%.pH sensitivity analysis showed that the Smart films change the color by changing the pH level,from pink at pH lower than 6 to yellow at pH higher than 6.Thus,the developed pH-sensitive films show band gaps in visible light that make them useful for monitoring milk spoilage.
基金financially supported by National Natural Science Foundation of China(22178242)Natural Science Foundation of Shanxi Province(202103021224101).
文摘In this study,chitin microcapsules were synthesized via the sol-gel method and subsequently functionalized through the encapsulation of curcumin and alizarin.These microcapsules were then incorporated into a polybutylene terephthalate adipate(PBAT)matrix at varying ratios to fabricate active smart packaging membranes.Microscopic morphology(SEM)analysis revealed that the microcapsules exhibited an ovoid morphology.X-ray diffraction spectroscopy(XRD)and Fourier Transform Infrared Spectrometer(FTIR)analyses showed that curcumin/alizarin does not alter the crystal structure of the microcapsules and that there are hydrogen bonding interactions with the microcapsules.To enhance antimicrobial performance,zinc oxide nanoparticles(5 wt%)were introduced into the composite film.Notably,the composite film with a microencapsulation content of 3 wt%exhibited an inhibition rate of 95.7%and 98.3%against E.coli and S.aureus,respectively.Finally,the composite films were assessed for their ability to monitor shrimp freshness.The results indicated that the films not only extended the shelf life of shrimp but also functioned as an effective freshness indicator by signaling spoilage.
基金supported by the National Natural Science Foun-dation of China(Nos.22268005 and 22178074)Natural Science Foundation of Guangxi Province,China(Nos.2019GXNSFDA245020 and 2020GXNSFGA297001)China Postdoctoral Science Foundation(Nos.2023MD734150).
文摘Using biodegradable films as smart packaging to monitor the freshness of meat in real time is a promising and challenging work.Herein,the phosphorus-doped carbon dots(P-CDs)with pH sensitivity were coated on starch/polyvinyl alcohol film(SP film)by a simple scrape-coating method and applied to monitor the freshness of pork.The P-CDs@SP film exhibits a uniform surface,excellent mechanical properties,higher light blocking.When the total volatile base nitrogen(TVB-N)of pork exceeded 15 mg/100 g,the color of the film changed from brownish-yellow to purple-red,and the total color difference(ΔE)of the film obviously increased from 10.24 to 9.37 to 20.75 and 22.93 under the storage conditions of 25 and 4℃,respectively.This can be attributed to the abundant hydroxyl groups on the surface of P-CDs and SP film to promote their stable binding through hydrogen bonds,which greatly improves the hydrophilicity of the films,providing conditions for the rapid conversion of the TVB-N to ammonia and the formation of an alkaline environment.This work can simply and effectively monitor the freshness of pork through the changes of film color,will provide a new idea for the preparation of biodegradable smart packaging materials.
基金This work was supported by Natural Science Foundation of Jiangsu Province(BK20210458,BK20201342)Young Elite Scientists Sponsorship Program by CAST(2021QNRC001).
文摘Ideally,packaging materials should ensure the safety and quality of foods,without contributing to environmental degradation.Consequently,there is interest in the development of biodegradable films assembled from natural materials,such as polysaccharides,proteins,lipids,and their mixtures.In this review,the physicochemical attributes and functional characteristics of biodegradable films prepared from these food-grade natural substances are summarized.Recent advances in the production of active and intelligent packaging materials are also discussed.Active packaging is designed to improve the shelf life of packaged foods by including antimicrobials or antioxidants,such as essential oils.Intelligent packaging is designed to provide real-time information about the quality,freshness,or safety of packaged foods by including indicators in the film that are responsive to changes in storage conditions,gas levels,pH,etc.Potential applications of intelligent and active packaging materials to fruit,vegetable,meat,seafood,and dairy products are discussed.
文摘The utilization of natural preservatives and active packaging in extending the shelf life of food products during storage is vital to meet consumer demand for minimally processed food under sustainable systems.Fiber and nanofiber,isolated from cells of different biologically active plants,possess antimicrobial activity and can be used as packaging material with an active ingredient.Soluble or insoluble fibers incorporated into edible films or coatings are particularly popular as functional food additives because of their characteristics.Moreover,fiber serves as an excellent packaging material with mechanical strength,antimicrobial properties,water vapor and oxygen permeability,high phenolic content,and thermal stability and therefore can be enhanced by the incorporation of different ingredients,which is also discussed in this work.It has been found that fiber and nanofiber based edible packaging materials can inhibit the growth of pathogenic bacteria and lipid oxidation.Furthermore,substantial changes have been reported in the surface morphology and mechanical properties of films/coatings with the addition of fiber based active materials like beta-glucan,pectin,guar gum,inulin,psyllium,cellulose,hemicellulose,chitosan and lignin.Hence,the existing literature articulates recent developments and their applications.Therefore,fiber/nanofiber can be a promising substitute for synthetic preservatives.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(2023R1A2C1005569).
文摘Phycoerythrin(PE)extract from red algae Laver(Pyropia dentata)was used in the fabrication of a smart pack-aging film.The PE showed pH sensitivity,implying unique color shifts at different pH.The film colors altered from red through purple-brown to colorless with increasing pH.The smart packaging films were prepared by casting method composed of gelatin(GE),sodium alginate(SA),and cellulose nanofibrils(CNF).The films were coded as GE/SA(control),GE/SA/PE,and GE/SA/CNF/PE.The thickness of the films ranged from 0.24±0.02 mm to 0.33±0.01 mm.The mechanical properties tensile strength(TS)(12.24±0.30 MPa to 17.65±0.33 MPa)and elongation at break(EAB)(79.34%±1.02%-93.36%±0.69%)significantly increased after addition of CNF.The synthesized films showed water contact angle ranged from 84.55±2.12 to 69.41±1.21,suggesting that films were hydrophobic.The Fourier transform infrared spectroscopy(FTIR)and X-ray diffraction(XRD)analysis demonstrated strong interaction among PE,CNF,and biopolymers.The film with GE/SA/CNF/PE exhibited higher thermal stability compared with control film.Then,the films were applied for checking real time application for the freshness of salmon fish.The significant color change of the film occurred and the number of bacterial colony and TVB-N were increased from 3.81 Log CFU/g to 6.94 Log CFU/g and from 4.78 mg/100 g to 32.27 mg/100 g after incubation for 48 h.Therefore,the film with PE and CNF was intended as an excellent candidate for smart packaging film.
基金funded by National Natural Science Foundation of China(31571788)Self-developing Instrument and Equipment Project of Yangzhou University(zzyq2022zy20).
文摘Freshness indicating labels embedded with pH-sensitive anthocyanins are one type of smart packaging tech-nology.However,the application of freshness indicating labels is mainly restricted by the high cost and hy-drophilicity of the labels.In order to reduce the manufacturing cost,passion fruit(Passiflora edulis)peel powder rich in dietary fibers and anthocyanins was used to prepare freshness indicating labels in this study.Moreover,the prepared labels were further soaked in 0.01,0.05 and 0.1 mol/L of stearic acid ethanol solution to increase the hydrophobicity of the labels.Structural characterization results showed the surface of the labels was covered by self-assembled stearic acid crystals.Stearic acid treatment significantly decreased the moisture content(16.90%→10.92%),hydrophilicity(water contact angle of 40.36°→103.01°),water vapor permeability(18.68×10^(-11) g m^(-1) s^(-1) Pa^(-1)→8.10×10^(-11) g m^(-1) s^(-1) Pa^(-1))and water uptake ability of the labels,which effectively prevented the leak of anthocyanins from the labels.In addition,stearic acid treatment greatly elevated the inner compactness of the films,resulting in improved tensile strength(3.12 MPa→6.18 MPa)and thermal stability.Moreover,stearic acid treatment well maintained the pH-dependent color changeable ability of the labels.The labels changed from reddish brown to olive and brown in the application of shrimp freshness indicating.When the labels were buried in natural soil at 20℃ for 10 days,82.74%-98.83%of the labels could be degraded.Therefore,this study provides a new and facile way to prepare freshness indicating labels.
基金financially supported by the National Key R&D Program of China[2022YFD2100500]the National Natural Science Youth Fund Project[32202043]the Student Innovation Training Program[202310057017].
文摘Smart packaging with colorimetric pH indicators is vital for food quality monitoring.However,synthetic pH-sensitive dyes pose safety hazards,and conventional methods to fabricate pH-sensitive films lack real-time detection.In this study,blueberry anthocyanin(Ant)and petunia dye(PD)were chosen among six natural dyes due to their enhanced pH responsiveness.They were utilized as chromogenic agents,while petunia dye composite film(PDCF)and anthocyanin composite film(AntCF)were synthesized using electrostatic spinning that incorporated natural dye,chitosan(CS),trehalose(TRE),and polyvinyl alcohol(PVA).Finally,a“sandwich”structure pH indicator was created by overlaying two layers of PET on the top and bottom of the composite film and perforating one side.The pH indicator based on PD composite film(PDCF-s)demonstrated superior effectiveness and stability compared to the Ant composite film(AntCF-s)in monitoring pork freshness.The indicators exhibited excellent sensitivity to low concentrations of ammonia vapor,completing the reaction within 2 min.As the pork spoiled,the color of PDCF-s changed visibly from pink to purple,with anΔE value of 40.Moreover,theΔE variation remained stable across different conditions.This study innovatively designed“sandwich”pH indicators,providing a promising natural safe dye for smart packaging,and promoting the use of pH-responsive indicators.
