Synthesis And Antimicrobial Activities Of Sulfonated Chitosan

Chitosan,as one kind of recyclable alkaline polysaccharide,has many advantages such as safe,nontoxic,biodegradable,biocompatible and film-forming properties.Chitosan has three types of reactive functional groups,an amino group as well as hydroxyl groups at the C-2,C-3 and C-6 positions,which makes it more suitable for chemical modifications.Chemical modifications of these groups have improved its bioactivities and provided numerous useful materials in different fields of application.In this study,to improve water solubility and antimicrobial activity,sulfonated chitosan was obtained by introducing 1,3-propane sultone onto the backbone of chitosan.The study is aimed at providing theoretical basis for the application of chitosan as food preservative,fruit and vegetable fresh-keeping agents.(1)In this study,renewable chitosan was chosen as starting material,sulfonated chitosan(SCS)was prepared via a facile chemical procedure by using 1,3-propane sultone attached to the backbone of chitosan.The resulting chitosan derivative was characterized by Fourier transform-infrared(FT-IR)spectroscopy,nuclear magnetic resonance(NMR)spectroscopy,gel permeation chromatography(GPC),elemental analysis(EA),and thermo gravimetric analysis(TGA),of which GPC was used to measure the molecular weight,EA for component analysis and TGA to determine the stability of SCS.(2)The in vitro antimicrobial activities of water soluble chitosan(WCS)and sulfonated chitosan(SCS)against Escherichia coli(E.coli)and Staphylococcus aureus(S.aureus)were investigated.Results showed that the minimum inhibitory concentration(MIC)of SCS against E.coli,S.aureus were 0.13 mg/mL and 2.00 mg/mL,while that of water-soluble chitosan(WCS)were 0.50 mg/mL and 4.00 mg/mL.It can be indicated that SCS exhibited better antibacterial activities than WCS and also E.coli is more sensitive to WCS and SCS in comparison with S.aureus.(3)Two strains were isolated and purified from decayed blueberry.To further confirm identity of the causal fungi,pathogenicity test,morphological characteristics and rDNA-ITS(internal transcribed spacer)sequence analysis were conducted.On the basis of above tests,one pathogenic fungus was indetified as Penicillium sp,another fungus indetified as Arthrinium sacchari(A.sacchari)was found out with no pathogenic ability to blueberry.Similarly,antifungal activities of WCS and SCS was performed on the major pathogen of blueberry(Botrytis cinerea,B.cinerea)and the two isolates,and the effect of WCS and SCS on blue mold infection of blueberry was tested.Results demonstrated that WCS exhibited higher antifungal activities against B.cinerea,Penicillium sp.,A.sacchari with MIC of 0.13 mg/mL,0.25 mg/mL,16.00 mg/mL than those of SCS with MIC of 0.25 mg/mL,0.50 mg/mL,64.00 mg/mL.In the mycelial growth inhibition experiment,the results showed that both WCS and SCS exhibited 100%radial growth inhibition against B.cinerea at a concentration of 4 mg/mL,while the antifungal indexes of WCS and SCS against Penicillium sp.were 100%and 90.4%,against A.sacchariwere 74.5%and 81.8%,respectively,even the concentration up to 16 mg/mL.The results indicated that B.cinerea and Penicillium sp.are highly susceptible to both WCS and SCS than that of A.sacchari.In order to explore the mechanisms of the antifungal activity of WCS and SCS,scanning electron microscopy was used to investigate the morphological changes of mycelia,the results revealed that WCS and SCS could damage and deform the structure of fungal hyphae with different action modes.Besides,it showed that WCS and SCS significantly reduced decay of postharvest blueberry.