| In the past decades,traditional petrochemical food packaging has caused pollution and non-biodegradable negative effects on the environment,which has aroused wide attention to these environmental problems.Starch as a cheap,natural and renewable resources,has good biodegradability,has become one of the most potential development of packaging materials.At present,due to the advantages of simple operation,mild conditions and direct continuous preparation of nanofibers,the preparation of starch film based on electrostatic spinning technology has become a research hotspot in the industry.However,the existing preparation of starch-based nanofiber membranes are based on toxic solvents such as formic acid or DMSO,and the electrospun membranes prepared by these methods are used as food packaging membranes,which has certain safety risks.Therefore,it is urgent to develop new green preparation methods of starch based nanofiber membranes.In this context,a new type of green starch based nanofiber membrane was successfully prepared based on electrospinning technology with sodium octenyl starch succinate（OS starch）as the main film forming material,Pullulan polysaccharide（PUL）as the auxiliary film forming material and water as the only solvent.The preparation and physicochemical properties of active nanofiber membrane with catechin/β-cyclodextrin inclusion complex were explored.Furthermore,in order to improve the water stability of active nanofiber membranes,the crosslinked nanofiber membranes were prepared by vapor crosslinking with glutaraldehyde,which showed good mechanical properties,strong barrier and excellent hydrophobic properties.Finally,the crosslinked nanofiber film was applied to the preservation of green tea and fresh pork,which verified the feasibility of the application of crosslinked nanofiber film in food packaging.The main contents and research conclusions include:（1）The feasibility of OS starch and PUL blending silk was explored,and a new green starch based nanofiber membrane based on organic solvent free system（water system）was successfully prepared.On this basis,the factors affecting spinnability of OS starch and PUL blend solution and the physicochemical properties of the corresponding electrospun film were further studied.Based on the experimental analysis of scanning electron microscopy（SEM）,it is found that the necessary conditions for the formation of continuous,smooth and beaded nanofiber membranes are as follows:The total content of OS starch and PUL is 20%-30%,the ratio of OS starch to PUL is less than 2:1（i.e.the content of OS starch is less than 20%）,the spinning voltage is 26～30 KV,and the feed rate is less than 1.4 m L/h.The diameter of OS starch/PUL nanofiber membrane fiber is in the range of 98.23 nm-156.86nm,the porosity is more than 87%,the water stability is poor（more soluble in water）,the mechanical properties（tensile strength and elongation at break）is poor,there is a large room for improvement.（2）The effects of catechin and catechin/β-cyclodextrin inclusion complexes on the physical and chemical properties of OS starch/PUL films were studied.It was found that with the addition of catechin and itsβ-cyclodextrin inclusion complex,the viscosity of spinning solution increased,the conductivity decreased and the diameter of nanofibers increased.The tensile strength was improved slightly.The highest tensile strength was obtained when catechin content was 1000 mg/L and clathrate content was4400 mg/L.Weak peaks were observed in the X-ray diffraction pattern,and peak movement was also observed in the infrared spectrum,indicating that catechin and catechin/β-cyclodextrin inclusion complex have been successfully encapsulated in the fiber membrane.The addition of catechin and catechin/β-cyclodextrin inclusion complex can improve the thermal stability of nanofiber membrane.The thermal decomposition temperature was increased from 297℃to 306℃and 323℃respectively.The effect of catechin on the thermal stability of nanofiber membrane was not significant,and the addition of inclusion compound was more obvious,becauseβ-cyclodextrin and catechin jointly improved the thermal stability of the fiber membrane.In addition,its antibacterial and antioxidant capacity was improved.After40 days of storage,the antioxidant capacity of the fiber membrane with catechin directly added was lower than 75%,and the free radical scavenging efficiency began to be lower than 80%.The nano fiber membrane with catechin/β-cyclodextrin inclusion complex maintained antioxidant level and free radical scavenging rate above 80%after40 days of storage.Therefore,its antioxidant performance is better.Then,antibacterial experiment on nano-fiber membrane with catechin/β-cyclodextrin inclusion complex was conducted,and it was found that the antibacterial zone was obvious,and the higher the concentration of inclusion complex,the higher the antibacterial rate,the more obvious antibacterial effect.（3）The fiber membrane was modified hydrophobic by using the steam crosslinking method of glutaraldehyde,and the influence of different crosslinking time on the nanofiber membrane was studied.It was found that during the crosslinking process of glutaraldehyde,aldehyde group and starch hydroxyl group underwent acetylation reaction,resulting in a significant reduction of the hydrophilic hydroxyl group in starch molecules,so no peak movement was detected through infrared.Only the peak enhancement occurred at 3320 cm-1.The thermal stability of the fiber membrane is improved slightly by crosslinking.The hydrophobicity and mechanical properties of the fiber film have the most obvious changes,and the contact Angle directly increases from 0°to 91.5°.It can also be seen from the water vapor transmittance and water solubility that the fiber film is very soluble in water,and the hydrophobic effect is relatively obvious through the crosslinked fiber film.The tensile strength of the crosslinked membrane increased significantly from 1.86 MPa to 19.16MPa,and the tensile strength increased nearly 10 times,which greatly improved the mechanical strength of the fiber membrane.In addition,the cytotoxicity test of Escherichia coli and the biocompatibility test of rat microfiber cells confirmed that the crosslinked membrane had no cytotoxic effect.（4）The effects of crosslinking on the antioxidant and antibacterial properties of nanofiber membranes were studied.The experimental results showed that the antioxidant and antibacterial activity of the nanofiber membrane did not decrease significantly after the glutaraldehyde vapor crosslinking,and its properties remained basically unchanged.By cross-linking fiber membranes containing catechin/β-cyclodextrin inclusion complexes with different contents,the effects of cross-linking membranes as food packaging membranes on Laoshan green tea and fresh pork were investigated.The changes of tea polyphenol content,vitamin C content,free amino acid content and antioxidant capacity of Laoshan green tea during storage and the changes of sensory characteristics,p H value,color and ferrimyoglobin content of pork during storage were analyzed respectively.It was found that due to the effect of catechin on oxygen isolation ability,compared with pure OS starch/PUL crosslinked membrane,The effect of crosslinked film packaging with catechin/β-cyclodextrin inclusion complex is significantly better,so that food quality can be better maintained during storage. |
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