Development And Application Of Colorimetric Indicator Materials For Chilled Pork Freshness Based On Natural Pigments

Chilled pork is a popular food source that is rich nutrition and good sensory quality;however,like other meats,it is easily contaminated by a variety of factors during transport,storage and distribution.Therefore,it is necessary to monitor chilled pork freshness.Spoiled chilled pork releases volatile nitrogenous substances,and generally known as total volatile basic nitrogen(TVB-N),which could lead to p H change of the surrounding environment.These p H-sensitive pigments are used to trace the p H changes,and accurate monitoring the freshness and spoilage of food.In this study,diblock copolymers and microspheres were used to encapsulate natural pigments to prepare colorimetric tablets and colorimetric microspheres to visualize the freshness of chilled pork,which is expected to be used in the field of meat freshness indication.The main research elements and results are as follows.(1)To improve the stability of natural pigments.Diblock copolymers(MPEG-PCL)were synthesized by the conventional ring-opening polymerization ofε-caprolactone using monomethoxyl poly(ethylene glycol)(MPEG)as a initiator.Alizarin-loaded MPEG-PCL micelles were fabricated using a solvent evaporation method.After freeze-drying,colorimetric tablets were fabricated by compression to monitor the freshness of chilled pork.The composition,molecular weight,structure and thermal properties of the polymer were characterized by Proton nuclear magnetic resonance(~1H NMR),Fourier transform infrared spectroscopy(FTIR),Differential scanning calorimetry(DSC).The morphology and size of the micelles were observed by Transmission electron microscope(TEM).TEM results shows that diameter of 35.9 nm of alizarin-loaded nanospheres were successfully prepared.Ultraviolet visible spectroscopy(UV-vis)showed that the light absorption peak of alizarin solution shifted to a longer wavelength as the p H increased.A gradual color changes has been observed in alizarin solution from yellow to purple at p H ranges 2～12.The colorimetric tablets were sensitive to four different concentrations gaseous ammonia of brown to purplish red or dark purple.When applied in monitoring chilled pork freshness at 4°C,the colorimetric tablets indicated sensitively with vision recognizable color changes from yellow to purple,the chilled pork corruption on the 4th day as TVB-N of reached 23.1 mg/100g and total viable count(TVC)reached 6.23 lg CFU/g.Moreover,a strong and positive correlation was obtained between theΔE values of the colorimetric tablet and TVB-N,p H,TVC and thiobarbituric acid reactive substances(TBARS)in chilled pork.The colorimetric tablet could effectively monitor chilled pork in real time and the color changes were easily distinguished by nake eye.(2)On the basis of ensuring the stability of natural pigments,improve the contact area between the intelligent packaging and TVB-N.Anthocyanin as the freshness indicator,sodium alginate were used as wall material to prepare microcapsule by ionotropic gelation.After freeze-drying,colorimetric microspheres were formed to monitor the freshness of chilled pork.The rheology behavior of microspheres-forming solution were investigated.The morphology and structure of colorimetric microsphere were characterized using Scanning electron microscope(SEM),FTIR,X-rays diffraction(XRD)and DSC.The 2,2-Diphenyl-1-picrylhydrazyl(DPPH)to characterize the antioxidant activity of the colorimetric microspheres.SEM results show that porous colorimetric microspheres with a diameter of 2.5～2.7 mm were successfully prepared.The colorimetric microspheres showed high stability after with 4°C and 25°C for one month of storage,whichΔE change of less than 5.The UV-vis showed that the light absorption peak of anthocyanin solution shifted to a longer wavelength as the p H increased.A gradual color changes has been observed in anthocyanin solution from red to purple and yellow green at p H ranges 2～12.The colorimetric microspheres were sensitive to four different concentrations gaseous ammonia of light pink to gray or black.When applied in monitoring chilled pork freshness at 4°C,the SA/A1 colorimetric microspheres indicated sensitively with vision recognizable color changes from red to colorless,the chilled pork spoiled on the 8th day as TVB-N of reached21.3 mg/100g and TVC reached 6.17 lg CFU/g,which highly correlated with theΔE values of the colorimetric microspheres and TVB-N,p H,TVC and TBARS value of chilled pork.The colorimetric microspheres could effectively monitor chilled pork in real time and the color changes were easily distinguished by nake eye.