Preparation And Properties Of Chitosan Oligosaccharide Derivatives Based On Modification On Hydroxyl Group

Nowadays,people are demanding higher and higher quality of food.Food additives from natural substances become more and more popular such as chitosan oligosaccharides(COS).COS,a kind of natural polysaccharide,is considered as a safe,non-toxic food additive that can extend the shelf life of food and improve food quality.However,COS has poor antimicrobial activity,while numerous studies have focused on the modification of COS to improve its antimicrobial activity.The antimicrobial activity of COS can be improved by introducing the active group on the site of hydroxyl group and remaining the amino group to effectively enhance its antimicrobial activity,because the amino group has antimicrobial activity.In our study,three different compounds with antimicrobial activity were used to modify COS.The structures of COS derivatives were analyzed by Elemental analysis,UV-vis absorption spectroscopy(UV-vis),Fourier transform infrared(FT-IR),~1H nuclear magnetic resonance(~1H NMR),X-ray diffraction(XRD)and Thermogravimetric analysis(TGA).We also investigated its solubility and antimicrobial activity.The main conclusions were as follows:(1)The O-2,4-dichlorophenoxyacetic-oligochitosan(COS-O-2,4-D)was synthesized by COS and 2,4-dichlorophenoxyacetic acid.The steps were as follows:the amino group of COS was protected firstly and the hydroxyl group of COS was reacted with 2,4-dichlorophenoxyacetic acyl chloride,the final products were obtained through deamination.COS reacted with 2,4-dichlorophenoxyacetic acid in different molar ratios(1:1,1:2 and 1:3),the yields were 77.39%,83.55%and 85.27%,respectively,the degrees of substitution were0.168,0.249 and 0.319,respectively.The results showed that crystallinity,thermal stability of COS-O-2,4-D were higher than that of COS.Compared with COS,the solubility of COS-O-2,4-D in ethanol,ether and DMF was increased,while the solubility in water was decreased.The antibacterial activity of COS-O-2,4-D against Escherichia coli and Staphylococcus aureus was 1.86~2.20 times and 1.38~1.58 times as much as that of COS.(2)The O-monomethyl fumaric-oligochitosan(COS-O-MFA),grafted monomethyl fumaric acid into COS,was synthesized by protection,substitution and deprotection reaction.COS-O-MFA were obtained by reacting COS with monomethyl fumaric acid in different molar ratios(1:1,1:2 and 1:3),the yields were 68.05%,73.59%and 79.76%,respectively,the degrees of substitution were 0.093,0.168 and 0.260,respectively.The results showed that crystallinity,thermal stability and solubility in DMF of COS-O-MFA were higher than that of COS,while the solubility in water was decreased.The antibacterial activity of COS-O-MFA against Escherichia coli and Staphylococcus aureus were 3.93~4.22 times and 1.90~3.20 times as much as that of COS,the antifungal activity against to Saccharomyces cerevisiae and Aspergillus niger of COS-O-MFA were 5.13~5.68 times and 6.74~7.22 times as much as that of COS.(3)Cinnamic alcohol was replaced the hydroxyl groups of COS to obtain COS derivatives(COS-O-Cin),a four-step reaction was taken as follows:the amino groups on COS were firstly protected using benzaldehyde by way of Schiff based reaction,fellowed by the preparation of cinnamyl bromide.And then,the N-benzylidene COS was reacted with cinnamyl bromide,finally,the COS derivatives were obtained by removing the benzylidene group.The final products were obtained by COS reacted with cinnamic alcohol in different molar ratios(1:1,1:2 and 1:3),the yield were 51.48%,55.97%and 58.11%,respectively,the degree of substitution were 0.064,0.128 and 0.188,respectively.The results showed that crystallinity,thermal stability and solubility in ether and DMF of COS-O-Cin were higher than that of COS,the antibacterial activity against Escherichia coli and Staphylococcus aureus of COS-O-Cin were 6.17~7.37 times and 4.79~5.14 times that of COS.In summary,the crystallinity,thermal stability and antimicrobial activity of three synthesized COS derivatives were higher than that of COS,COS-O-MFA and COS-O-Cin have significant inhibitory effect on fungus and bacterium,respectively,that was suggested the great potential as new bacteriostatic agents in food fields.