| The overuse of plastic packaging has caused serious environmental problems.Chilled meat production and transportation are carried out under non-freezing conditions,which provide favorable conditions for microbial growth and oxidation,which cause serious losses to the meat industry.Active packaging and intelligent packaging can delay the deterioration of food quality and monitor food quality in real time.Watermelon rind is rich in many active ingredients,but the utilization rate is very low.In view of the low utilization rate of watermelon by-products,the quality of chilled beef and mutton deteriorated rapidly in the process of logistics and marketing,and the lack of freshness monitoring technology,this study took watermelon peel as raw materials,and adopted co-extraction technology to extract pectin(WMP)and polyphenol(WME).Active packaging film and intelligent indicator label were prepared by dielectric baffle discharge(DBD)plasma modified WMP.In order to provide scientific basis and practical reference for the development of green,environmentally friendly,efficient and intelligent new materials for chilled meat,and help to reduce the environmental damage caused by traditional plastics from the source,and promote the resource utilization of watermelon peel.The main findings are as follows:1.Study the optimal parameters of watermelon peel pectin and polyphenol co-extraction process,build an extraction model,and analyze the watermelon peel structure changes during the extraction process.Under the conditions of liquid-solid ratio 29,p H 2.7,ultrasonic power 573 W and ultrasonic time 52 min,the maximum yield of pectin and polyphenol was 16.37% and 3.91%,respectively.Compared with traditional extraction methods,co-extraction had the highest pectin extraction rate(PE)and dissolution rate,while the activation energy(Ea)of polyphenols extraction was lower.The whole watermelon skin was honeycomb,and the pectin extraction was more complete after the extraction,indicating that the co-extraction process was helpful to improve the yield of pectin and polyphenols from watermelon skin.2.The effects of WMP functional characteristics and extraction process on the functional characteristics of pectin and polyphenols were investigated.In the co-extraction process,WMP has lower ash content,higher protein content and solubility,showing light yellow color,uniform particle distribution,lower molecular weight,but more concentrated,lower degree of methyl esterification,higher degree of acetylation,lower content of galacturonic acid,longer side chain and shorter main chain in RG-Ⅰ region.WMP is a low methoxy pectin with low crystallinity.WMP has high emulsifying stability,and the solution is pseudoplastic non-newtonian fluid with shear thinning characteristics.The contents of monophenols and antioxidant properties of WME were significantly higher than those of traditional methods(P <0.05),which indicated that watermelon peel was the source of high-performance pectin and co-extraction improved the properties of pectin and polyphenols in watermelon peel.3.The effects of DBD plasma treatment on the physicochemistry,structure,function and properties of WMP films were investigated.Compared with the original pectin,the water content,molecular weight,methylation and acetylation degree of pectin were significantly decreased(P < 0.05),while the protein content,b* and solubility were significantly increased(P < 0.05)with the increase of DBD plasma treatment voltage or time.HG region of pectin was degraded and RG-Ⅰ region was retained after treatment.The surface of pectin was reticulated and cotton flake.The crystal type of pectin did not change,but due to oxidation and depolymerization,pectin O-H bond decreased and C=O bond increased.The thermal stability and emulsification stability of WMP increased,while G’ and G "increased.In addition,with the increase of treatment voltage or time,the thickness,solubility,OP,WVP,EAB and Sq of the films were significantly decreased(P < 0.05),while the TS was significantly increased(P < 0.05),indicating that DBD plasma treatment improved the properties of pectin and films.4.4.Explore the effects of different WME supplemental levels on the properties of modified WMP-based active packaging film and its preservation effect on chilled mutton.With the increase of WME supplemental level,the thickness,b* and △E of the films were significantly increased(P < 0.05),while the solubility and L* were significantly decreased(P < 0.05).There was no crack on the film surface,but Sq increased significantly(P < 0.05),and thermal stability increased.Due to the increase in the number of hydrogen bonds between WME and WMP molecules,when the amount of WME was ≤1.5%,WME significantly decreased the WVP,OP,EAB of the thin films(P < 0.05),and the light barrier properties and TS were significantly increased(P < 0.05),indicating that the appropriate amount of WMP could improve the performance of WMP thin films.In addition,the p H value,L*,b*,storage loss,cooking loss,TVB-N,TBARs and TCA of the film group were significantly lower than those of the other groups(P < 0.05),and the shear force,a * and sensory score of the film group were significantly higher than those of the other groups(P < 0.05),which could prolong the shelf life of chilled mutton to 35 d.The results showed that the film could delay the deterioration of quality of chilled mutton during storage.In addition,during storage,the surface of the film became rough,the thickness and EAB increased significantly,and the TS decreased significantly(P < 0.05),but no cracks appeared,indicating that the film has stable properties and is suitable for the preservation of cold mutton.5.The influence of different amount of PCE on the performance of modified WMP-based intelligent indicator label and its application in monitoring the quality change of chilled mutton were investigated.The color of PCE solution changes from pink to yellow as the p H value increases from 2 to 11.With the increase of PCE content,the Sq,thermal stability,free radical scavenging ability,antibacterial properties,a*,b* and △E of the films increased,while the phototransmittance and L*decreased.PCE was physically and chemically connected in WMP pectin group.When the addition level of PCE was not higher than 1.5%,the label OP,WVP and EAB were significantly decreased,while the LABEL TS was significantly increased(P < 0.05).WMP/PCE1.5 had the best color stability and p H response.With the prolongation of storage time,the L*,b*,p H,TVB-N and TCA of chilled mutton were significantly increased,while a* and sensory score were significantly decreased(P <0.05).The spoilage of chilled mutton was reached on day 8,and the color of WMP/PCE1.5 changed from pale purple to pale blue.It indicates that WMP/PCE intelligent indicator label has the potential of monitoring the deterioration of chilled mutton quality.6.The influence of different amount of BTE addition on the performance of modified WMP-based intelligent indicator label and the quality change of chilled beef were investigated.As the p H value increases from 3 to 10,the color of the BTE solution changes from pink to bright yellow.With the increase of BTE,the Sq,thermal stability,a*,b*,△E and color stability of the films increase,while the transmittance and L* decrease.BTE is physically and chemically connected in WMP films.When BTE supplemental level was lower than 2%,OP,WVP and EAB of labels were significantly decreased(P < 0.05),while TS was significantly increased(P < 0.05)with the increase of BTE supplemental level.In addition,with storage time prolonging,p H,TVB-N and TCA of chilled beef were significantly increased,while sensory score was significantly decreased(P < 0.05).According to the least partial square method(PLS-DA)analysis,TVB-N was the most important factor affecting the shelf life of chilled beef,and the chilled beef reached spoilage at 8d,and the color of WMP/BTE label changed from pink to brown accordingly.The results showed that WMP/BTE intelligent indicator label has the potential of real-time detection of chilled beef quality changes.In conclusion,watermelon peel is a high-quality source of pectin and polyphenols.Co-extraction process can improve the quality of pectin and polyphenols.DBD plasma can improve the performance of pectin and film. |
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