Preparation And Characterization Of Chitosan Nanofibers With Fruit And Vegetable Preservation Function

Marine polysaccharide (such like chitosan) is a kinds of the rich natural bioactive substances. Numerous studies shows that chitosan has excellent antibacterial properties, biocompatibility, biodegradability, permeability and processing performance, so the studies based on the chitosan has become to a hot research topic. In the previous study, our research group already completed the preparation of edible chitosan films and chitosan composite films, also provided the chitosan/alginate, chitosan/?-carrageenan composite film preparation technology. At the same time, proposed that the chitosan with excellent processing performance and safety.Nanofibers with great specific surface area, excellent breathability, moisture retention properties, flexibility and adsorption performance, makes it as a hot topic of materials science. Researches on nanofiber preparation method has been quite mature, traditional methods still in use, novel methods also endless. However, the preparation approach of nanofbers perfect for chitosan, and applied for food packaging are rarely reported, most cases are the prepared chitosan nanofibres not suitable for food packaging materials, or suitable for food packaging materials can't use chitosan nanofibres as raw materials, even or the prepared nanofibers has many limiting factors, such as cumbersome and complex steps, largely consuming energy, fibers with large diameter, difficult to control the orientation, can not get rid of the shackles of chemical solvents, etc., which largely limits the application of chitosan nanofibres in food packaging.This study based on the the chitosan aerogels which was successfully obtained by using ice templating technique in our research group, proposed a novel chitosan nanofibers fabrication technique which combined ultrasonic atomization and freeze casting. The full text from the view of method exploration; parameter optimization; analysis and enhancements of the physical and mechanical properties; functional coating of filter paper; antimicrobial testing; fresh fruits and vegetables preservation, etc., to explore the potentials of the ultrasonic atomization-freeze casting chitosan nanofibres in food packaging. 1 Proposal and parameter optimization of ultrasonic atomization combined freeze casting for chitosan nanofibersAligned chitosan nanofibers exhibiting diameters smaller than 100 nm were easily prepared by combining ultrasonic atomization with freeze casting. This simple method exhibited excellent fiber formability using water as the main solvent, minimizing volatile organic solvent use, made the obtained chitosan nanofibers safety, environmental friendly and compatibly. Scanning electron microscopy demonstrated that fiber diameter and morphology mainly depended on the atomizing tools, freezing temperature, and chitosan solution viscosity. Minimum diameter and uniform orientation were achieved using an electric flosser as an atomizing tool, liquid nitrogen as a coolant,0.4 wt% aqueous chitosan solution (molecular weight=22 kDa), and a small amount of lactic acid as solvent at 0?.2 Performance analysis and enhancements of ultrasonic atomization-freeze casting chitosan nanofibersUltrasonic atomization-freeze casting chitosan nanofibers were easily curly deformed after encountering water, soaking for 24 h, the nanofibers film texture tend to gel but without dissolve. Moisture absorption rate was 33.56%, moisture retention rate was 20.9% and the specific surface area was 19.318 m2/g. Chitosan nanofibers both obtained by PSAF and airbrush with poor mechanical properties, makes it difficult to direct application as a functional materials in its present form. Compress the chitosan nanofiber into film is an effective way to improve the performance of ultrasonic atomization-freeze casting chitosan nanofibers. Solubility in water (from rapidly curly deformed after encountering water to keep relatively stable after soaking in water for 24 h) and moisture absorption rate (19.57%) of chitosan nanofibers was significantly reduced after pressed into film, seems like the serious pressure, the smaller solubility and moisture absorption rate. However, although the sensory mechanical properties of chitosan nanofiber was improved significantly, but the fiber diameter forced to increase (from 390 nm to 475 nm) and the specific surface area forced to reduce (Manual press was 10.423 m2/g, hydraulic press was 3.7140 m2/g).3 Functional coating of cellulose filter paper with ultrasonic atomization-freeze casting chitosan nanofibersFunctional coating of cellulose filter paper is a simple and effective way to apply of ultrasonic atomization-freeze casting chitosan nanofibers. With the help of cellulose filter paper, the poor mechanical properties of chitosan nanofibers can be improved; due to the chitosan nanofibers coating, the specific surface area and antibacterial properties of cellulose filter paper also improved. PSAF single atomizing showed the best coating effect with the average chitosan nanofibers diameter of 234.96 ± 68.36 nm. In the case of the presence of water, chitosan nanofibers almost impossible to maintain the original morphology after complete crosslinking with the TPP. Also, atomizing of chitosan and TPP crosslinked gel basically can't get fibers. Chitosan and TPP atomizing together or tandem atomizing with poor reproducibility and controllability limit its use.4 Antibacterial properties of ultrasonic atomization-freeze casting chitosan nanofibersChitosan nanofibres with different form and morphology, the antibacterial properties shows obviously differentiation. Antibacterial properties from best to worst:chitosan nanofibers coated filter paper, chitosan nanofibers crosslinked with TPP and then coated filter paper, hydraulic compressed chitosan nanofibers film, untreated chitosan nanofibres. Chitosan nanofibers within the scope of this study, overall shows obvious inhibition of Bacillus subtilis, followed by Escherichia coli, and Staphylococcus aureus. From the point of view of antibacterial, chitosan nanofibres obtained by ultrasonic atomization combined with freeze casting is suitable for use as a functional food packaging materials.5 Fresh fruits and vegetables preservation properties of ultrasonic atomization-freeze casting chitosan nanofibersFrom the view of strawberry perspectives sensory evaluation, weight loss rate, rotten rating, Vc content after storage for 5 days, ultrasonic atomization-freeze casting chitosan nanofibers coated filter paper showed excellent fruit preservation performance. It can extend the shelf life and prevent moldy of the fruit and vegetables, also effectively preserve nutrients, so we can say it should be an ideal packaging material. However, the current performance of chitosan nanofibres compared with plastic wrap in the storage of fresh fruits and vegetables, in addition to effectively prevent spoilage bacteria to breed, no other obvious advantages. Especially from the view of maintaining moisture and the Vc content of the strawberry. For the moment, not as good as the traditional plastic wrap, it is necessary to look for other media through alternative cellulose filter paper, to explore better coating solutions.