| Packaging could effectively protect fresh food from a variety of environmental factors(oxygen,moisture,light,etc.),significantly prolong the shelf life,and is of great significance to the transportation,storage and sales of fresh food.However,there are two main problems in the use of traditional fresh food packaging:firstly,petroleum based plastics caused serious environmental pollution.Secondly,the function of traditional packaging for fresh food is single,which can not meet consumers'demand for freshness and safety products.Existing studies have shown that bioplastics and natural polymers could not only degrade naturally,but also design and manufacture functional composite films.Therefore,based on PLA,the basic membrane was prepared by nano strengthening,and then the active layer was compounded in situ by electrospinning technology to prepare three kinds of functional composite membranes;At the same time,the deep learning model was applied to the design of migrating antibacterial composite membrane;Finally,the functional composite film was used for the preservation and storage of fresh agricultural products(fish,cucumber),so as to prolong the shelf life and intelligently indicate the freshness.This paper mainly includes five parts:1.Study on the effect of nano particle on PLA film.In this paper,polylactic acid(PLA)membrane was strengthened with nano Zn O,nano Mg O,nano NCC,nano Zn O/Mg O.It was found that the nano materials were evenly distributed in the polylactic acid biofilm,and there was no new chemical bond with the polymer.The mechanical properties of PLA membrane were improved by four kinds of nano materials.The effect of adding 2%nano Mg O oxide was the most significant,which the TS,EM and EAB increased by 54%,48%and 13%respectively.The OP of PLA membrane added with 1%nano Zn O decreased by 21%compared with the control group.The hydrophilicity of PLA membrane can be significantly reduced at the level of 2%(P<0.05).In addition,PLA membrane was endowed with good UV absorption ability,and the effect was the best when the addition amount was 2%Zn O,which can absorb more than 90%UV.Nano NCC could enhance the thermal stability of PLA membrane.In conclusion,nano materials can effectively improve the performance of PLA membrane.According to different requirements,corresponding nano materials can be selected to prepare reinforced PLA membrane,which provides a basic membrane for the further development of subsequent double-layer functional composite membrane.2.Development and application of pH intelligent indicating composite membrane.Anthocyanins were mixed into zein solution and compounded in situ on the basic membrane by electrospinning.It was found that the surface morphology of composite membrane did not change with the addition of anthocyanins.Under ammonia simulated conditions,the composite membrane has obvious color response within 20 min,which change from purplish red to brown.The change rate of total color difference(?E)of the composite membrane with 40%anthocyanin addition was the largest,indicating that its color change was the most easily observed;The relative color change(S)rate of 20%anthocyanin composite membrane was the highest,indicating that its color change was the most sensitive;In the storage test of 30 days,the?E value of membrane(20%anthocyanin)was the lowest,indicating that the stability of it was the best.It was applied to the freshness monitoring of fresh fish stored at room temperature.It was found that the discoloration time of the composite membrane was the second day.At this time,the TVB-N content and the total number of colonies in the fish were close to or exceeded the national standard limit,and the composite membrane with 20%anthocyanin was sensitive and stable.It showed that the composite membrane as pH indicator can intelligently indicate the corruption process of fresh fish.3.Study on composite membrane with renewable antibacterial function.A layer of polyvinyl alcohol(PVA)was compounded in situ on PLA/Mg O basic film by electrospinning.Based on the principle of molecular branching,chlorogenic acid(CA)was fixed on the surface of PVA in the presence of photoinitiator benzophenone tetracarboxylic anhydride(BD)molecule.The results of SEM showed that the molecular branching treatment had no significant effect on the morphological structure of the membrane surface,and the structure of PVA nanofibers remained intact.NMR spectra showed that BD,CA and BDCA were bound to PVA by chemical bond rather than physical adsorption.Grafting treatment could improve the surface hydrophobicity of the membrane,and the increase rate of the contact angle of PVA-BDCA composite membrane was the largest,up to 44%;Whether under light or dark conditions,the composite membrane has antibacterial effect on Escherichia coli and Listeria monocytogenes,and antibacterial rate under light conditions was about twice that under dark conditions,and the logarithm of the total number of colonies can be reduced by about 3;Moreover,the production of free radicals was also the largest;After UV irradiation,the antibacterial properties and free radicals of PVA-BDCA composite membrane could be produced repeatedly until the composite membrane breaks after 5 cycles.This also showed that the regeneration of the antibacterial function of the composite membrane was realized by generating free radicals by UV circulation.4.Application of deep learning in the design of migrating functional composite membrane.This section collected the migration related data of 99 groups migration active membranes,established the relationship between migration influencing factors and initial addition through deep learning neural network model,and then predicted the minimum initial addition,and then prepared the migration functional membrane according to the prediction results and characterized whether it has application value.The prediction results showed that the minimum concentration of eugenol was 0.1245%,and the R~2of the model was 0.7097.According to the prediction results,the initial addition concentrations were 0.2%,0.3%and 0.4%,and the base membrane was polylactic acid.Then the gelatin solution containing eugenol was compounded in situ on the surface of the base membrane by electrospinning technology.The characterization results show that the morphology of the nanofibers in the surface active layer was uniform and smooth,and the average diameter was 157?293 nm.The addition of eugenol improved the surface hydrophobicity of gelatin nanofibers,and its contact angle increased by 62%,but had no effect on its thermal stability,barrier and mechanical properties.The composite membrane had good antioxidant capacity,and its antioxidant capacity and free radical scavenging rate have a good dose-response relationship.The linear correlation coefficients were 0.9900 and 0.9975,respectively.The three membranes had antibacterial activity against Escherichia coli and Staphylococcus aureus,and the antibacterial performance increased linearly with the increase of eugenol content.The composite membrane had inhibitory effect on Escherichia coli and Staphylococcus aureus,and the inhibitory ability was positively correlated with the amount of eugenol in a dose-dependent manner.Among them,the composite membrane with 0.4%eugenol had the best antibacterial effect,and the total number of colonies decreased by 3(Escherichia coli)and 2.5 logarithms(Staphylococcus aureus)respectively.This shows that the migration composite membrane prepared according to the model prediction has significant antibacterial and antioxidant capacity.5.Application of migration antibacterial composite film in Cucumber preservation.The migration antibacterial composite film was used for the preservation of Cucumber under the storage condition of 4°C.The results showed that compared with unpackaged cucumber(CK),the total loss and its change rate of cucumber packaged with P0(Cucumber packaged in composite film without eugenol)and P1,P2 and P3(Cucumber packaged in composite film with 0.2%,0.3%,and 0.4%eugenol)were significantly reduced(P<0.05),and the total loss was reduced by about 33%on the 15th day.Compared with CK and P0,the total color difference and its change rate of P1,P2 and P3 decreased significantly(P<0.05),and decreased by about 20%on the 15th day.In addition,the activities of POD,SOD,CAT and proline in P1,P2 and P3 were significantly higher than those in CK and P0,and their change rates were also significantly different(P<0.05),while the content of total sugar,MDA and their change rates were significantly lower than those in CK and P0,indicating that eugenol can stimulate the production of self oxidase and proline and delay the postharvest senescence of cucumber.The total number of colonies of P1,P2 and P3 was significantly lower than that of CK and P0,and their change rates were also significantly different(P<0.05),indicating that the composite membrane had good antibacterial effect.Further analysis showed that the effect of P2 was better than P1 and P3,and the shelf life of cucumber was extended from 15 d to 21 d.Therefore,the antibacterial composite membrane added with 0.3%eugenol can be used to prolong the storage life of fresh cucumber,and has good application potential. |
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