| As the second largest producer of mangoes in the world,the mango industry brings huge economic benefits to the people every year in our country,and mango peel is one of the main wastes in mango processing,containing a lot of polysaccharides,polyphenols and other active substances.However,in addition to a small part for compost,feed and other low value-added products,most of them are directly discarded,which pollute the environment and cause a waste of resources.In this study,three kinds of mango peel extracts(MPE)were prepared by different solvents and methods,and the main components of MPE were characterized and analyzed.Furthermore,three kinds of composite films were prepared with polymer materials,which provided a certain theoretical basis for the application of mango peel waste in film materials.Three MPEs were extracted by the following methods:(1)The extraction solvent was ethanol: ethyl acetate(m:m=6:2),and ultrasonic-assisted extraction was used,glycerol:PEG400(m:m=3:1)as a plasticizer.The extraction rate of MPE is 24.13%.The number of average molecular weight(Mn),the weight average molecular weight(Mw),and the polydispersity coefficient of MPE is 2096,2049,1.149,whose content about the total polysaccharide(TPS),the total polyphenol(TPP),and the total flavonoid(TF)is 13.38 g CE/100 g,3.05 g GAE/100 g,0.27 g CE/100 g separately.(2)The extraction solvent was ethanol: ethyl acetate(m:m=6: 2),and microwave assisted extraction was used.The extraction rate of MPE is as high as 38.26%,Mn is 2002,Mw is 2275,polydispersity coefficient is 1.136,TPS is 36.98 g GE/100 g,TPP is 13.74 g GAE/100 g,TF is 1.43 g CE/100 g;(3)Using dichloromethane as a single solvent and extracting with the aid of ultrasound.The extraction rate of MPE is only 1.52%,Mn is 1325,Mw is 1340,polydispersity coefficient is 1.011,TPS is 15.76 g GE/100 g,TPP is 8.13 g GAE/100 g,TF is 1.17 g CE/100 g.In the further prepared MPE/PVA composite film,the MPE and PVA are mainly connected by hydrogen bonds and newly formed ether bonds.Adding an appropriate amount of MPE can improve the accumulation of the PVA matrix and improve the water resistance and mechanical properties of the film.Compared with pure PVA film,the elongation at break of 3MPE/5PVA composite film was increased by 196.0%,reaching1329.5%.At the same time,the film had good UV barrier,oxidation resistance and certain antibacterial properties.The second prepared PVA/CS/MPE composite film had greatly improved antibacterial properties and exhibited good degradability.In the case of no plasticizers,the elongation at break of PVA/CS-CA/MPE composite film was more than doubled compared with that of pure PVA film.At the same time,the water resistance of PVA/CS-AAG film with the addition of MPE was greatly improved.The third composite film was first prepared by using MPE to synthesize MPE/AgNPs,which was proved to be successfully synthesized by XPS and XRD characterization.Furthermore,PLA/MPE/AgNPs composite film was successfully prepared by using polylactic acid(PLA)as a protective agent and film-forming material.TEM showed that PLA can effectively prevent the excessive agglomeration of AgNPs,and the particle size of AgNPs was reduced from 2.5-6.5 nm to 1.0-3.4 nm.Similarly,the composite film still exhibited good UV barrier properties and oxidation resistance.At the same time,the composite film had good physical properties,and the water vapor transmission rate(WVTR)and oxygen transmission rate(OTR)were lower than pure PLA film.In addition,the composite filmhad an inhibition rate of more than 95% against escherichia coli and staphylococcus aureus,and the amount of silver migration was also in accordance with the European Commission No.10/2011.The direct contact method was used to determine the toxicity of the composite membrane to L02 cells,and the cell survival rate exceeded 80%.Strawberry was used as the test subject for sensory evaluation,the composite film showed excellent fresh-keeping ability,and the strawberry did not rot within 7 days. |
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