| Nanofibers have been widely used in the fields of biomedicine,tissue engineering,environmental protection and food field because of the advantages of high surface area and high porosity,and electrospinning is the only technology to prepare continuous nanofibers currently.In recent years,the preparation of nanofibrous membranes with natural green safety and natural antibacterial and antioxidant properties has become a hot topic in the research of food packaging.Research showed that propolis had strong bioactivity such as oxidation resistance and antibacterial activity.It is expected to prepare nanofiber membrane by electrospinning.However,pure propolis needs high polymer as an auxiliary carrier before spinning.The natural polymer polysaccharide konjac glucomannan has a large molecular weight,and has good film forming,gelatinous and water holding properties.It can be used as a polymer carrier to prepare the propolis-konjac glucomannan nanofiber membrane.Therefore,this study used the natural polymer polysaccharide konjac glucomannan as the carrier and added propolis to prepare the propolis-konjac glucomannan nanofiber membrane.By changing the properties of the spinning solution and the parameters of the electric field,the conditions of the preparation of the nanofiber membrane were optimized in order to prepare the good propolis-konjac glucomannan nanofiber membrane.The microstructure of nanofibers was observed by SEM.The interaction between components was analyzed by FTIR.DSC was used to evaluate the thermal stability of nanofibers.The spinning electric field was simulated by ANSYS finite element software,the distribution rule of field strength was explored,and the effect of spinning electric field on fiber morphology was verified.Finally,the fish meat preservation experiment on nanofiber membrane was carried out,which provided a theoretical basis for the application of propolis nanofiber membrane in food preservation.The main contents and results are as follows:(1)The mass fraction and electric field parameters of each component in spinning solution usually have a great influence on the morphology of nanofiber membrane.In a certain range,konjac glucomannan,as the carrier of the spinning solution,dissolved in water to form a sol and made the spinning solution spinnable.After experiment,we could see that when the concentration of konjac glucomannan was lower than 0.6%or higher than 0.8%,the spinnability and fiber morphology were poor.As a solute,high content of propolis could destroy the network structure of konjac glucomannan and water molecules,and the spinnability was reduced.The results showed that when the content of propolis was below 0.035%or more than 0.050%,the fiber would be broken and unevenly.It was suitable when the content of konjac glucomannan was 0.6%,and the content of propolis extract was 0.050%.The spinning process also has a certain degree of influence on the morphology of the fiber membrane.On the premise of determining the properties of the solution,the spinning voltage,distance and speed were set 16-28 kV,16-22 cm and 0.4-0.7 mL/h,respectively.Through SEM observation and diameter analysis,when the spinning voltage was 24 kV,the spinning distance was 18 cm,and the spinning flow velocity was 0.5 mL/h,the diameter of nanofibers was uniform and the morphology was better.The reaction of konjac glucomannan and propolis was found by Fourier transform infrared spectroscopy.The DSC diagram showed that the thermal stability of the nanofiber membrane was improved after the addition of propolis,indicating that the propolis nanofiber membrane with Konjac Glucomannan as the carrier was successfully constructed in this study.(2)The effect of spinning voltage and spinning distance on the spinnability and fiber morphology of the nanofiber film was investigated by the finite element simulation of the spinning field by ANSYS.In the case of other conditions unchanged,the spinning voltage was set 16 kV,20 kV,24 kV and 28 kV respectively,and the spinning distance was set 16 cm,18 cm,20 cm and 22 cm,respectively.The vector distribution of the electric field intensity and the potential of the electric field and the change of the electric field intensity were obtained.It could be seen that the vector distribution of the electric field intensity and the potential of the electric potential were distributed centrally along the spinning needle.The strength of the electric field at the nozzle of the spinneret was the greatest.The strength of the electric field would increase with the increase of the spinning voltage when keeping the receiving distance and the spinning flow velocity unchanged.When the voltage was lower or higher,the interaction between the positive and negative poles was large and the potential distribution was unstable.The spinning environment was not conducive to the formation of high quality nanofibers at this time.Keeping the spinning voltage and spinning speed unchanged,the potential distribution and electric field intensity distribution from different receiving distances could be seen that when the receiving distance was less than 18 cm,the interaction between positive and negative electrodes was obvious,so the electric field was unstable.With the increase of the receiving distance,the interaction between positive and negative electrodes decreased,and the distribution of electric field was stable.At this time,the electric field environment could spun the nanofiber film with better morphology.With the increase of the receiving distance,the distribution of the potential was more and more unbalanced.This was due to the distance between the positive and negative electrodes was increased and the interaction of electric field force was weakened.It was concluded that 18cm was a suitable receiving distance.The finite element software ANSYS was used to simulate the electric field.The simulation and electric field distribution calculation of the spinning device under different spinning voltage and distance parameters could provide a more intuitive understanding of the spinning electric field,and further verified the influence of electric field on the fiber morphology.(3)In the storage process,grass carp is prone to corruption and deterioration,mainly due to the destruction of cathepsin and microbes in the muscles of the body,so that the fish is corrupted and deteriorated.This research studied the fresh-keeping effect of grass carp of propolis nanofiber membrane carried by konjac glucomannan and explored the possible mechanism of its preservation.Through the observation of changes in appearance and sensory evaluation of fish under cold storage,it was found that the untreated fish began to deteriorate after placing 4 d,and the spoilage was obvious after 8 d stored.However,the deterioration process of fish packaged with nanofiber membrane was slower,indicating that this nanofiber membrane could delay the deterioration of fish and prolong the shelf life of fish.The change of pH in fish first decreased and then increased gradually.The content of MDA and peroxide value increased with time,but wrapped nanofiber membrane of the fish,the MDA content and the peroxide value increased more slowly,indicating the nanofiber membrane could slow the deterioration of fish meat and had a certain preservation of the fish meat.The results provide a theoretical basis for its application in food preservation. |
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