| Meat is rich in protein and is an important type of food in human’s daily diet.It is highly susceptible to spoilage due to microbial contamination,fat and protein oxidation,and cannot be judged by the naked eye in the early stage.Intelligent indicator film directly reflects the freshness of meat food by the color change of the film,thus achieving non-destructive detection.Among them,anthocyanin,as a kind of natural,non-toxic and safe indicator,presents obvious color changes under different pH conditions,but anthocyanin itself is unstable and easily affected by external environment such as temperature and light,resulting in the poor stability of single-layer anthocyanin indicator film,while the double-layer composite film is helpful to enhance its stability and achieve more accurate non-destructive testing of meat foods.In this paper,emerald blueberry was selected as the experimental material,and the anthocyanin was obtained by solvent extraction method,and its characterization and light and temperature stability were studied,chitosan and soluble starch were used as the inner film substrate,different additions of blueberry anthocyanins were added to the inner film,sodium alginate and soluble starch were used as the outer film substrate,the bilayer composite film was prepared by two-step casting method,and the performance of single and double layer indicator films with different additions of blueberry anthocyanins were measured and characterized.Single and double layer indicator films with the best overall performance were selected for freshness indication of pork at different storage temperatures(25℃ and 4℃),and the correlation analysis between the color difference value(ΔE)of the film and total volatile basic nitrogen(TVB-N)in pork was performed to verify the accuracy of the test results.The study in this paper is as follows:(1)Extraction of blueberry anthocyanins and its propertiesBased on the final results of the single-factor test,the orthogonal test was conducted by selecting the volume fraction of ethanol,extraction temperature and extraction time as the main influencing factors,and the optimal extraction process was obtained by range analysis and variance analysis:the material-liquid ratio was 1:20 g:mL,the volume fraction of ethanol was 80%,the extraction time was 50 min,and the extraction temperature was 50℃,and the extraction amount of blueberry anthocyanin was 7.99 mg/g at this time.The color variation of blueberry anthocyanins in pH 1-13 solution:red→light red→ lavender→ grayish purple→ blue-green→ green,its UV spectrum showed the maximum absorption peak and absorbance changed,and the Fourier transform infrared(FT-IR)spectroscopy showed the absorption peak region of blueberry anthocyanin.Light and temperature stability studies of blueberry anthocyanin storage for 60 h showed that the preservation rate under dark conditions was 1.20%higher than under light conditions,the preservation rate at 4℃ is 2.90%higher than that at 25℃,and the preservation rate at 25℃ is 8.06%higher than that at 37℃,so light-proof and low-temperature conditions should be chosen for storage.(2)Preparation of blueberry anthocyanin indicator film and its performance studyThe optimal process parameters for the outer layer film were determined by singlefactor tests as follows:sodium alginate concentration of 2%,soluble starch concentration of 4%,and the volume ratio of sodium alginate to soluble starch of 5:5,at which the tensile strength of the outer layer film was 7.41 MPa and the elongation at break was 69.62%.When different amounts of blueberry anthocyanins were added to the single-layer films,the transparency,mechanical properties,and water content of the films gradually decreased and the water solubility gradually increased with the increase of blueberry anthocyanins content.Compared with the single-layer film,the mechanical properties of the double-layer film increased,the water content and water solubility decreased,and the overall performance of the bilayer-film was improved.The pH sensitivity and ammonia sensitivity of the double-layer film lagged slightly,but the color change was still obvious to the naked eye,and the stability of its own storage was better.At 6 d of storage at 25℃,the color difference value of the double-layer film with 8%blueberry anthocyanin addition was 29.48%lower than that of the single-layer film,which could extend the service life by 3-4 d.Thermogravimetric analysis showed that the addition of blueberry anthocyanin could improve the thermal stability of the film,and the stability of the double-layer film was better than that of the single-layer film in the range of 0℃-200℃.FTIR spectra showed that blueberry anthocyanin had been successfully embedded into the film matrix,and no new structures were generated in both single and double layer films,and the chemical composition was not affected.Scanning electron microscopy(SEM)showed that the addition of 8%blueberry anthocyanin indicated good membrane compatibility,and the cross-section of the double-layer showed a more complete bilayer characteristic,no breakage or aggregation between the films,and tight bonding between the films.(3)Study on nondestructive detection of pork freshness with blueberry anthocyanin indicator filmsSingle and double layer indicator films added with blueberry anthocyanins at 8%were applied to the freshness indication of pork at different storage temperatures(25℃and 4℃).The drip loss rate,pH,total viable count(TVC),TVB-N value and color difference between single and double layer indicator films were measured.The results showed that after 30 h of storage at 25℃,the pork had a drip loss rate of 8.43%,pH value of 6.40,TVC value of 7.27 1g CFU/g and TVB-N value of 24.92 mg/100 g,at which time the pork had deteriorated.After 8 d of storage at 4℃,the pork had a drip loss of 6.00%,pH value of 6.57,TVC value of 7.32 1g CFU/g,and TVB-N value of 25.81 mg/100 g,at which point the pork was spoiled.During the storage process,both single and double layer indicator films could change color from purple to gray to bluegreen,and the polynomial model fit of ΔE value of the indicator film and TVB-N value of pork was high,and they were significantly positively correlated,so both single and double layer indicator films could be used for freshness detection of pork.The single-layer film is easy to be destroyed during application due to high water solubility,while the double-layer film has better integrity and better stability,so it has more promising application. |
PDF Full Text Request