The Effect Of Acid Disturbed Fermentation On The Physical Properties Of Bacterial Cellulose

As new ideal biological nanometer materials,bacterial cellulose has many particular physical properties such that it can be widely used in various industries.However,with the development of bacterial cellulose,the requirements of its crystallinity,holding water capacity and other physical properties are become higher.Furthermore,the nature of bacterial cellulose has not fully satisfied the industrial production.Generally,we use the method of modification to solve this problem.Nevertheless,the chemical modification is difficult and low safety.Hence,many researchers have been focused on the biological modification,the safely and effectively control the physical properties of bacterial cellulose will become the inevitable trend in the future.This paper studies the biological modification of bacterial cellulose.Based on the experiment,we found that the bacteria in fermentation could produce a large of outgrowth acid,which can reduce the pH value of fermentation liquid,influence the production of cellulose synthase and cellulose,and change the thickness and aperture of cellulose at the same time.Hence,from the experiment of acid disturbance,utilizing the Gluconacetobacter hansenii HDM,Gluconacetobacter hansenii high-producing bacterium HDCo-5 and low-producing bacterium HDBr-12 to study the physical properties variation of bacterial cellulose under the acid disturbance,the aim is to adjust the biological modification of cellulose crystallinity,mechanical strength and physical properties to satisfy the requirement in many industries.The main results as follows:Test the Gluconacetobacter hansenii high-producing bacterium HDCo-5.Using the pyruvic acid,citric acid and acetic acid in metabolic pathway as perturbation,the normal pH5.8 as control group,we compare with the physical properties variation of cellulose under the fermentation extremum pH3.5.The results show that adding three kinds of acid can increase weight the dry film,water-holding capacity and rehydration rate,while the average weight of dry film is increased by 10%,and the tensile force of film decreases.Measured in crystallinity,crystallinity was increased by 5%due to add the pyruvate,and was reduced by 30%and 9%based on the addition of citric acid and acetic acid,respectively;Clustering analysis found that the pH variation only impact on the physical properties a little,and the type of the acid is more noticeable effects on physical property of cellulose.Therefore,acid disturbance can change the physical properties of bacterial cellulose,especially the crystallinity.Crystallinity has become important in cellulose application,in order to get high crystallinity in acid disturbance,based on the above method,this experiment consider crystallinity as the testing indexes,compare with 3 strains in the metabolic pathway of pyruvic acid,citric acid,acetic acid and lactic acid and hydrochloric acid,respectively,to determine the disturbance acid in the metabolic pathway.Furthermore,from the detection of disturbance acid concentration and the crystallinity time,compare with the results of H+ ion and acid radical ion effect on crystallinity,determine the ideal acid disturbance environment in order to get the highest degree of crystallinity.The results show that the degree of crystallinity is highest in pyruvate acid as the disturbance acid,and it higher than other acid by 10%?20%;When the amount of disturbance acid in pyruvate was 0.3%,strains of crystallinity were significantly increased.Hence,the best acid disturbance environment is:acid disturbance is pyruvate;Addition amount of acid is 0.3%;The addition time is the third day of fermentation.Acid radical ion can increase crystallinity of filaments by about 10%.Principal component analysis found that the difference of strains can impact on the cellulose obviously,the change of pH weaker influence on cellulose.H+ ion and the acid radical ion effect on the crystallinity existence of bacterial cellulose are not independent,but affect the physical properties of cellulose together.Specially,the acid radical ion had a greater influence on the crystallinity of cellulose.In order to better understand the best acid disturbance environment to get the highest degree of crystallinity,we consider other changes in the physical properties of the fiber produced by three strains.These experiment results show that moisture rate,recovery rate of water absorption,tensile force,TPA index,filaments and crystallinity degree of 3 strains are increasing with the extension of fermentation time,the biggest increase strain HDCo-5 rise about 10%on average.Clustering analysis found that strain HDM and HDBr-12 have the similar physical properties in fermentation for 5 and 10 days.But fermentation for 15 days,strain HDM and HDBr-12 have the similar physical properties of HDCo-5 for 5 and 10 days,respectively,and the other physical properties of HDCo-5 are all different from the strain HDM and HDBr-12.It also found that the physical properties of bacterial cellulose were related to its nature,the physical properties of strains HDCo-5 are different from HDM,the reason may be the mutations in bacteria.Generally,the acid disturbance can change the physical properties of the bacterial cellulose.Acid disturbance environment of highest crystallinity degree is the third day to join the pyruvate with the 0.3%concentration.Different strains in different fermentation periods,the physical properties of cellulose have significant changes,and the physical properties of the bacterial cellulose are greatly influenced by strain itself.