Preparation Of Electrospun Nervilia Fordii’s Extraction Nanofibrous Mat And Its Properties

Currently,the biobased polymers and the natural compounds（antibacterial agents,antioxidants,etc.）are attracting increasing attention to prepare environmentally and friendly efficient active packaging materials.Electrospinning is regarded as one of the simple and versatile methods to continuously fabricate nanofibers under mild operating conditions.The electrospun nanofibrous film possesses some excellent characteristics,such as adjustable diameter,high porosity and large area-to-volume ratio,leading to a great potential in the field of antioxidant packaging.Nervilia fordii（family Orchidaceae）,a well-known medicinal herb that mainly distributed in Southwest of China,has high content of phenol and flavonoid compounds,which play a role in antioxidant bioactivity.To date,there has been no report regarding the electrospinning of bio-polymers with Nervilia fordii extract（NFE）.Hence,in this study,the extraction process of Nervilia fordii was first optimized to obtain the NFE with high antioxidant activity.Then,two types of electrospun fiber mats were prepared by adding the anxioxidant NFE into the substrates of biodegradable polyvinyl alcohol/polyvinylpyrrolidone（PVA/PVP）and soybean protein isolate/pullulan polysaccharides（SPI/PUL）,respectively.The morphology,structure and antioxidant activity of obtained fiber mats were explored.The release mechanism of NFE from fiber mats in different food simulants were also investigated.The main research contents and results are as follows:（1）Preparation of Nervilia fordii extract and its antioxidant activityFirstly,the single factor experiment and response surface methodology were applied to optimize the water-ethanol extraction process of Nervilia fordii.Results showed that the optimum conditions were ethanol concentration of 56%,extraction temperature of 75 ^oC and solid-liquid ratio of 1:14,under which,the DPPH clearance rate of 2 mg/L NFE was 40.9%（similar to the theoretical predicted value of 41.5%）,indicating that the experimental model obtained was accurate and reliable.After that,the ethonal extract was extracted by petroleum ether,ethyl acetate,and n-butanol phase,respectively.Results indicated that the total flavonoids and polyphenol contents in ethyl acetate phase were the highest,which were 334.56 mg/g and 86.67mg/g,respectively,accordingly,the ability of DPPH scvenging rate(IC₅₀ 0.66 mg/mL)and lipid oxidation resistance(IC₅₀ 312.3 mg/mL)and reducing power ability were higher than the other three phases.Therefore,the ethyl acetate phase of NFE was adopted in the following study.（2）Preparation and characterization of electrospun polyvinyl alcohol/polyvinylpyrrolidone/Nervilia fordii extract fiber matFirstly,PVA/PVP/NFE electrospun fiber mat was fabricated by optimizing the solution composition and electrospinning parameters.The optimal electrospinning conditions were:10%PVA and 15%PVP were mixed in a 1:1 volume ratio,the concentration of NFE was 4 mg/mL,voltage 15 kV,feed rate 0.3 mL/h and distance 14 cm.Under which,the obtained PVA/PVP/NFE film had good morphology with average diameter being 280 nm.Then,attenuated total reflectance-fouriertransform infrared（ATR-FTIR）,thermogravimetric analysis（TGA）and X-ray diffraction were used to characterize the structure of the resulting nanofilm,and the results indicated that the NFE was embedded in the fiber and hydrogen bond interaction was occurred among PVA,PVP and NFE.DPPH analysis demonstrated that the obtained fiber mat exerted good free radical scavenging ability.To be specific,distilled water,3%acetic acid,10%ethanol,50%ethanol and 95%ethanol were chosen as food simulants for fatty foods,high-alcohol food or milk dairy products,alcoholic foods,acidic food with pH<4.5 and high water content foods,respectively.The release behavior of NFE from PVA/PVP fiber mat in the above simulants was studied.Results showed that the highest release of NFE was observed in 95%ethanol followed by that of in 50%ethanol,while the release amount of NFE from 10%ethanol,water and acidic food simulants were limited,indicating that the obtained PVA/PVP/NFE film is suitable for packaging of lipophilic foods.Mathematical model revealed that the release profile of NFE was fitted well by Ritger-peppas model in water,3%acetic acid and 10%ethanol,while in 50%ethanol and 95%ethanol Weibull model had the highest fitting degree.The release kinetics analysis showed that the release of NFE was controlled by fickian diffusion mechanism.（3）Preparation and characterization of electrospun soybean protein isolate/pullulan polysaccharide/Nervilia fordii extract fiber matIn order to obtain antioxidant packaging film with good performance for hyrophilic foods,SPI/PUL/NFE electrospun fiber mat was fabricated by electrospinning.The optimal electrospinning conditions were determined as:total polymer 30%,the ratio of SPI to PUL was3:7,2%F127,voltage 18 kV,feed rate 0.5 mL/h and distance 14 cm.Under which,the obtained SPI/PUL/NFE film had good morphology with average diameter being 240 nm.The results of FTIR and TGA indicated that the NFE was embedded in the fiber and hydrogen bond interaction was occurred among SPI,PUL and NFE.DPPH analysis also revealed the good antioxidant activity of obtained fiber mat.In contrast to PVA/PVP/NFE,in vitro release study showed that higher release amount and rate of NEF were achieved in the water,10%ethanol and 3%of acetic acid,while the release amounts of NFE from 50%ethanol and 95%ethanol were restricted.For SPI:PUL=2:8 fiber mat,higher fitting degree was achieved by Ritger-peppas model in water,suggesting the potential application for packaging of higer-water contents foods.Mathematical model indicated that the NFE release was controlled by anomalous transport（non-Fickian）mechanim in 3%acetic acid and 10%ethanol,while in 50%ethanol and 95%ethanol,the release of NFE followed fickian diffusion mechanism.