Study On Antibacterial Activity Of Lignin And Ways To Improve It

With the emergency of lignocellulosic refining technology,there is an increasing interest in exploring the valuable applications for lignin due to its abundant and underused features.Lignification of plants can enhance the antimicrobial ability of plants,originating from the physiological function of lignin in plants,the antimicrobial activities of lignin and ways to improve it were studied.Several kinds of lignins named as softwood alkaline lignin(SAL),softwood organosolv lignin(SOL),hardwood alkaline lignin(HAL),hardwood organosolv lignin(HOL),gramineae alkaline lignin(GAL)and gramineae organosolv lignin(GOL)were prepared from different sources and methods.The antibacterial activities of six kinds of lignin were evaluated.The results showed that six kinds of lignin had inhibitory effect on gram-positive bacteria,staphylococcus aureus and bacillus subtilis,gram-negative bacteria,Salmonella Enteritidis and Escherichia coli.However,lignin has stronger influences to G+than G-.Lignin may be more likely to damage the cell walls of G+and affect its growth and reproduction.According to the characterization results of six lignins,it was speculated that the antibacterial activity of lignin might be related to phenolic hydroxyl content.In general,alkali lignin extracted from the same source biomass has higher phenolic hydroxyl content and better antimicrobial activity than organosolv lignin and corn straw lignin contained had better antimicrobial activity with more phenolic acids.Then,considering the heterogeneity of lignin,the alkali extracted lignin from enzymatic hydrolysis residue in ethanol biorefining and bamboo-lignin were fractionated by ethanol-water system.The results showed that the lignin with antimicrobial activity was concentrated in the lower molecular weight fractions with higher phenolic hydroxyl content.The antibacterial mechanism of lignin was speculated by measuring the growth curve and observing the colony morphology by scanning electron microscopy,lignin affected the morphology of the bacteria.The results of flow cytometry showed that some of bacteria were killed by lignin.Then,moderate depolymerization via in situ ethanol/acid catalysis was used to increase the antimicrobial activity of corn straw alkali lignin.The results of molecular weight measurement showed that the molecular weight of lignin was decreased by depolymerization.The antimicrobial experiments showed that the antimicrobial activity of the depolymerized lignin was significantly increased.