Study On Surface Modification And Microbial Immobilization Of Porous Starch

Porous starch,a new type of modified starch,is formed by enzymatic hydrolysis of starch.Thanks to it has a lot of channels in the surface and its surface area has significantly higher than that of the original starch,porous starch has a better absorption ability.However,after the formation of porous starch,the overall structure of the particles is destroyed,and the structural stability and mechanical strength are reduced.The modification of porous starch with polyethyleneimine and glutaraldehyde could enhance its stability and mechanical strength.And the surface of the modified porous starch is covered with positive charge,which is easy to combine with the negative electric charges to improve its adsorption performance,and then open up a new field of applications for porous starch.In this paper,we used the corn starch as raw material,porous starch was prepared by method of enzymatic hydrolysis,and optimize the preparation conditions of porous starch,such as the ratio of starch added enzyme,an enzyme reaction influence factors such as temperature and reaction time and so on.Surface modification of porous starch was carried out with Polyethyleneimine used as modifier and glutaraldehyde used as cross-linking agent.The adsorption rate of methyl orange was used as index to determine the optimal reaction conditions.Finally,the modified porous starch was used as a carrier to immobilize the E.coli.Based on the experiment,the conclusion has been obtained as follow:(1)The optimal conditions for preparing porous starch by enzymatic hydrolysis method are:The amount of enzyme added was 6%of the corn starch content,the ratio of?-amylase and glucoamylase is1:6,reaction at 50?for 24 hours.The porous starch prepared under the optimal conditions has a large number of pores and a large pore size,and the external shape of the particles is relatively complete.(2)The optimum reaction conditions for porous starch surface modification as belew.10%porous starch 20 mL,0.06 g/mL polyethyleneimine was added to the reaction system for 6 hours,then 5%glutaraldehyde was added dropwise to continue the reaction for 2 hours.The modified porous starch obtained under this condition has the optimal adsorption effect on methylorange.The analysis of the surface characteristics of the modified porous starch by infrared spectroscopy.The results showed that the modified porous starch has a characteristic amino peak,which is positively charged,and it is easy to absorb negatively charged substances,The application is more extensive.(3)The modified porous starch was used as a carrier to immobilize E.coli,The optimal conditions of immobilization were 2 g modified porous starch,10~8cfu/mL concentration of E.coli,reaction time is 2 h,and rotation speed from 140 r/min to 170 r/min.Comparing the loading of E.coli with porous starch and modified porous starch,they were 1.63×10~9/g and 3.94×10~9/g,respectively.The effect of modified porous starch on the immobilization of E.coli was much better than that of porous starch.