| Meat and meat products are considered the best protein and vitamin sources.Also,they have high relative humidity,making them optimal for microorganisms to degrade the amino acids in protein and produce metabolites.Consequently,the freshness of the meat rapidly declines,resulting in limited shelf life.Even though the physical and chemical traditional methods may reliably assess meat freshness,however,they are time-consuming frequently and unable to capture the meat freshness in real-time.Concurrently,pH colorimetric films containing natural dyes-based biogenic amines-sensitive have been applied to monitor meat freshness.The smart pH colorimetric films offer intuitive and simple benefits and could visually indicate the quality of food freshness by monitoring color change.However,it has limitations because of the pigment’s low stability in UV light,film swelling,and dye leaching in a high-humidity environment.Therefore,in this study,typical meat freshness indicators and antibacterial films were developed.The films were produced on the basis of natural materials such as natural waxes(sugarcane wax,soybean wax,and sunflower wax)to take advantage of their hydrophobic properties to improve the property of blocking ultraviolet light,preventing high humidity swelling and reducing dye leaching from the film matrix containing natural anthocyanin dyes(butterfly pea flower,purple cauliflower,and Chinese purple cabbage)in order to enhance their ability to change their color when interacting with ammonia gas,in addition to the use of Origanum compactum essential oil as an antibacterial bioactive material.The results proved that these films are effective in monitoring the freshness of meat and have high efficiency in terms of resistance to ultraviolet light,preventing high humidity swelling,reducing dye leaching and antibacterial.The main research content and results are as follows:1.Development of pH colorimetric film with anti-ultraviolet light protection and study of its response optically to biogenic amines for tracking shrimp freshness.The anthocyanin of butterfly pea flower(BF)easily deteriorates under UV light,leading to the colorimetric film’s fading and loss of color sensitivity.In this study,sugarcane wax(SW)was used to protect the anthocyanin of BF from oxidation and color fading(by blocking UV light)to enhance the photostability of the indicator film.The agar(Agr)matrix was incorporated with various concentrations(1%,1.5%,and 2%w/v)of SW and combined with BF anthocyanin.SEM micrographs,XRD,and FTIR spectra were used to verify the efficiency of the incorporation of SW into the Agr-BF matrix.Then,the films’ illumination stability and sensing properties were investigated,and the films were used for monitoring the shrimp’s freshness.The results showed that combining BF anthocyanins with SW as lipid(hydrophobic)in films displayed perfect protection against UV light(0%)and a valuable reduction in visible light(45%).As well revealed the ability to change colors under two different ammonia vapors concentrations(50 and 100 mmol/L).The Agr/BF/2%SW film was chosen as a biomarker for the shrimp’s freshness due to its overall performance and apparent color sensitivity in the critical acceptance point with ΔE 11.55 at 25℃(9 h).In conclusion,the established film had a good ability to block UV light and could be used to indicate the shrimp’s freshness.2.Development of pH colorimetric films with anti-swelling properties(hydrophobic)for monitoring the shrimp freshness.The hydrophilic indicator films easily swell in a highhumidity packaging environment,leading to a decrease in anthocyanin content and a decrease in the accuracy of the film indication.In this study,hydrophobic films were prepared using soybean wax(hydrophobic)to enhance an anti-swelling property.This study tested the potential of using soybean wax(SBW)to protect the purple cauliflower(CF)anthocyanins from swelling from the indicator films and enhance their color change ability.The films were designed from SBW in several percentages(5%,10%,15%,and 20%w/w)and agar and methylcellulose matrix(AM)combined with CF anthocyanins.The results showed the color of the AM/CF/SBW films completely converted when exposed to ammonia vapors(100 mmol/L)with the highest sensitivity(38.5%,30 min)in the film containing 20%SBW,equivalent to the obtained color in the alkaline pH.Remarkably,the SBW films had significantly low swelling index(27.98%in the AM/CF/20%SBW film)and water vapor permeability(2.21*10-7mm-2.d-1.pa-1 in AM/CF/15%SBW).The colorimetric films with various percentages of SBW were made and applied to monitor the shrimp freshness with high color sensitivity.The color change in AM/CF/10%SBW film was ΔE 7.8 in the critical accepted point of shrimp at 25℃(9 h).In conclusion,the developed film had a good hydrophobic anti-swelling capability and could be used to indicate the freshness/spoilage of shrimp visually.3.Development of pH-colorimetric indicator films with high leaching resistance and response to biogenic amines to monitor chicken breast freshness.The hydrophilicity of anthocyanin leads to leaching in a high-humidity packaging environment,decreasing anthocyanin content in the films and reducing film sensitivity and color change.This study proposed using hydrophobic sunflower wax(SFW)to construct a hydrophobic environment in the film to block the dissolution and leaching of the anthocyanin.The film was fabricated from various concentrations(6%,9%,12%,and 15%w/w)of SFW combined with AM and Chinese purple cabbage(CPC)anthocyanins.After that,the films’ leaching release analysis and water vapor permeability were investigated.The leaching release analysis results of the CPC anthocyanin color indicated that the increase in SFW concentration led to decreased absorbance significantly(0.005)in food simulant(50%and 95%ethanol)for 10 h.Therefore,in 9%SFW the water vapor permeability was reduced to 2.15*10-7mm2.d-1.pa-1.The colorimetric films with various percentages of SFW were made and applied to monitor the chicken breast freshness with high color change sensitivity in the AM/CPC/9%SFW film(ΔE 7.31)at the critical accepted point of chicken breast at 25℃(27 h).Hence,the developed film had good anthocyanin leaching-resistant ability and was successfully applied to monitor chicken breast freshness.4.Development of hybrid films(active/intelligent pH colorimetric)for reducing bacterial spoilage and monitoring the freshness of the chicken breast and shrimp in real-time.The production of hybrid films has dual functions,which firstly can monitor food spoilage with a color change and,secondly,as an antibacterial to increase the shelf life of meat products and reduce food waste.In this study,the AM/CPC/9%SFW colorimetric film was selected as a carrier of the bioactive Origanum compactum essential oil(OC)in various concentrations(1%,1.25%,and 1.5%v/v).Then,the fundamental characteristics of the hybrid film,such as antibacterial and antioxidant activities and its response to ammonia vapor from chicken breast and shrimp,were explored.The results indicated that it rapidly responded to various pH(2-12)solutions,and NH3 gas reflected different colors.The hybrid films also prevented the growth of gram-positive bacteria(Staphylococcus aureus)and gram-negative bacteria(Escherichia coli),where the AM/CPC/9%SFW/1.5%OC hybrid film exhibited a large inhibition zone and attained diameters of 37.33 and 15.67 mm,respectively,in the disc diffusion test.During the storage period application,the AM/CPC/9%SFW/1.5%OC films extended the shelf-life of chicken breast and shrimp to 33 and 21 h with(ΔE)17.55 and 19.98,respectively,at 25℃.Accordingly,the developed hybrid film had good antibacterial properties and was effectively applied to monitor chicken breast and shrimp freshness.This study developed freshness indicators and antibacterial films based on different natural waxes and anthocyanins.As a result,this study presents a promising opportunity for potential future applications in monitoring the freshness of meat products. |
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