Study On Preparation Of Electrospun Polymers/Cinnamon Essential Oil Nanofibrous Films And Their Properties

Food antimicrobial packaging can efficiently inhibit the microbial growth on foodsurface, extend shelf-life and maintain the quality of the food. Among the various materialsused in food antimicrobial packaging, nano-scale antimicrobial packaging material hasattracted more and more attention due to its unique structure and property. Presently,electrospinning is the unique method to continuously fabricate nanofibers with mild operatingconditions. The electrospun nanofibrous film produced by electrospinning has some excellentcharacteristics such as adjustable diameter, high porosity and large area-to-volume ratio,leading to its great potential in the field of antimicrobial packaging. To date, there has been noreport regarding the electrospinning of polymers with essential oils, a kind of naturalantimicrobial agent, and their application in food antimicrobial packaging. Therefore, in thisstudy, electrospun nanofibrous films were firstly prepared by adding essential oil into thesolution of biodegradable polyvinyl alcohol (PVA) or polylactic acid (PLA), and then theirantimicrobial effects in packaging and storage of strawberry and pork were investigated.The main research contents and results of this paper are as follows:(1) Screening of plant essential oil.Cinnamon essential oil (CEO) was screened from four plant essential oils for its bestantimicrobial activity by filter paper diffusion method. It showed excellent antimicrobialactivities against four kinds of common foodborne microorganisms (Escherichia coli,Salmonella enteritidis, Staphylococcus aureus, Listeria monocytogenes).(2) Preparation of electrospun hydrophilic polyvinyl alcohol/cinnamon essentialoil/β-cyclodextrin (PVA/CEO/β-CD) antimicrobial nanofibrous film and its property.Firstly, the influence of the solution composition and electrospinning parameters wasinvestigated, and the optimal electrospinning conditions were: mass concentration of PVA,CEO and β-CD was6%,2%and2%, respectively, distance14cm, voltage15kV and flowrate0.4mL/h. Under the optimal conditions, the obtained hydrophilic PVA/CEO/β-CDnanofibrous film had good morphology with average diameter being240nm. Then,attenuated total reflectance-fouriertransform infrared (ATR-FTIR) and thermogravimetricanalysis (TGA) were applied to characterize the structure of the resulting nanofilm, and the results indicated that CEO was encapsulated into β-CD and the molecular interaction occurredamong PVA, CEO and β-CD. Finally, the antimicrobial results showed that the obtainednanofibrous film had excellent antimicrobial activity, as the inhibition rate against E.coli andS.aureus reached above90%when its concentration was4mg/mL (the corresponding CEOconcentration being80μg/mL). Compared with the antimicrobial film prepared by castingmethod, the electrospun PVA/CEO/β-CD nanofibrous film had better antimicrobial activity.(3) Preparation of electrospun hydrophobic polylactic acid/cinnamon essentialoil/β-cyclodextrin (PLA/CEO/β-CD) antimicrobial nanofibrous film and its property.Firstly, the CEO/β-CD inclusion complex was prepared by using CEO as core materialand β-CD as wall material. The influence of various factors was investigated, and theoptimum proportion of CEO to β-CD, encapsulating temperature and time were found to be1:9,55oC and3h, respectively. Under these conditions, the CEO loading content was117.2mg per gram β-CD. Then, the influence of the solution composition and electrospinningparameters was investigated, and the optimal electrospinning conditions were determined asthe mixed solution of dichloromethane (DCM): N, N-two dimethyl formamide (DMF)=3:1(v/v), PLA concentration10%(w/v), CEO/β-CD-IC concentration10%(w/v), voltage12kV,distance11cm and flow rate2.2mL/h. Under these conditions, the obtained hydrophobicPLA/CEO/β-CD nanofibrous film had good morphology with average diameter being320nmand CEO/β-CD aggregates were evenly distributed on the fibers. Subsequently, FTIR andDSC were taken for characterizing the structure of PLA/CEO/β-CD-IC nanofibrous film andthe results indicated that the molecular interaction existed among PLA, CEO andβ-CD.Finally, the antimicrobial results showed that the obtained nanofibrous film hadexcellent antimicrobial activity, as the inhibition rate against E.coli and S.aureus was around90%when its concentration was4mg/mL (the corresponding CEO concentration being46.88μg/mL), demonstrating its potential for the application in active food packaging. Similarly,compared with the antimicrobial film obtained by casting method, the electrospunPLA/CEO/β-CD nanofibrous film had better antimicrobial activity.(4)Application of PVA/CEO/β-CD and PLA/CEO/β-CD nanofibrous films.The antimicrobial effects of PVA/CEO/β-CD and PLA/CEO/β-CD nanofibrous films wereinvestigated by observing the appearance changes of strawberry and pork and detecting total bacterial number on the pork. The results showed that the strawberries without anypretreatment had decayed on the4thday, while there were no rotten phenomena on thestrawberries packaging with PVA/CEO/β-CD or PLA/CEO/β-CD nanofibrous films even atday6. For pork preservation, the bacterial numbers on the surface of control was above106CFU/g on the3rdday. However, the bacterial numbers on the surface of the samples packagedwith PVA/CEO/β-CD or PLA/CEO/β-CD nanofibrous films did not exceed106CFU/g untilthe7thday, suggesting that these two kinds of antimicrobial films can effectively prolong theshelf-life of strawberry and pork, thus potential for the application in the packaging ofdifferent kinds of foods.This study will form the basis for developing novel biodegradable nanofibrous packagingmaterial with antibacterial property, and promote its application in the field of foodantimicrobial packaging as well.