Studies Of Antimicrobial Edible Composite Films Based On Cellulose Sulfate

Edible antimicrobial film is a kind of functional thin layer by tape casting andcoating, which uses natural edible substance (such as proteins, polysaccharides, lipids, etc.)as raw material and is supplemented with antibacterial agent, and plays an importantrole on food packing. Cellulose sulfate (NaCS) is a kind of cellulose derivative,which is made form one or more hydroxyl groups of glucose unit being substituted bysulfate radicals. It has high research value in the field of edible film because of itsstrong hydrophilicity, good biocompatibility and excellent film-forming performance.In this paper, we improved the non-homogeneous process for preparing NaCS, andobtained two new edible antimicrobial films by using NaCS as film material, glycerolas the plasticizer, mustard essential oil (MO) and L. reuteri fermentation solution asantibacterial agent, respectively.Firstly, the non-homogeneous process for preparing NaCS was improved byusing sodium ethoxide for washing and neutralizing processes synchronously in newprocess. The infrared spectroscopy, X-ray diffraction and thermogravimetric analysisof products showed that improved process successfully obtained NaCS, and theproducts quality was almost the same before and after improvement. The yield andsubstitution degree of NaCS were81.83%and0.51in improved process respectively,which slightly increased than original process. Whereas NaCS solution viscosity (2%,v/v) of the improved process was1.6times as large as the original process, whichindicated that the improved process effectively solved the problem of hydrolysisproducts. Furthermore, We evaluated the storage stability, enzyme degradationperformance and salt tolerance of the NaCS in detail.Secondly, the NaCS-β-CD-MO composite films, which used NaCS, MO andβ-CD as films material, antibacterial agent and slow released agent respectively, wereprepared, and then the properties of composite films, such as antibacterial properties,slow release effect of MO, mechanical properties, barrier property, etc, were alsostudied. The results were as follow. The composite films had a certain inhibitoryeffect on Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Bacillussubtilis (B. subtilis) and Aspergillus Niger (A. Niger), especially on E. coli and S. aureus. β-CD on the MO had a significant role in the retention and sustained release,and the highest MO content of films containing β-CD was up to11mg/g, which was1.6times of films without β-CD. Composite films had excellent properties onmechanical properties, flexibility, oil-proofing, vapor-proofing, transparency andhydrophilic properties. With the increase of MO, the elongation at break (E%), watervapor permeability (WVP) and thickness of films increased, but the tensile strength(TS), young’s modulus (EM), water absorption rate (Wm) and transparency of filmsdecreased. In addition, the properties of films were analyzed by scanning electronmicroscope, Fourier infrared spectrum and X-Ray Diffraction. The results indicatedthat the composite films appeared phase separation between NaCS and β-CD, but MOin films could promote the compatibility among different components.Finally, the NaCS films incorporated with L. reuteri fermentation solution wereprepared. We analyzed the components of fermentation solution, and evaluatedproperties of films, such as antibacterial properties, mechanical properties, barrierproperty, etc. The results were as follow. The components of L. reuteri fermentationsolution were living bacterium of (3.85+0.05)×108cfu/mL, lactic acid of11.67±0.02g/L, glycerol of7.14±0.08g/L, acetic acid of15.05±0.03g/L. The compositefilms had significantly inhibitory effect on E. coli, S. aureus and A. Niger, especiallyon S. aureus. Composite films had excellent properties on mechanical properties,flexibility, oil-proofing, vapor-proofing, transparency and hydrophilic properties. Asthe content of L. reuteri fermentation solution increased, the E%, WVP, Wm andthickness of films increased, but the TS, EM, oil permeability, transparency andintegrity of films decreased. Besides, the properties of films were analyzed byscanning electron microscope, Fourier infrared spectrum and plate counting. Theresults showed that the components of films had good compatibility, but inactivationof L. reuteri appeared in the process of preparing films.