Methods for producing modified microcrystalline chitosan and uses therefor

Abstract

Disclosed are methods of producing modified microcrystalline chitosan. Chitosan in aqueous solution is degraded enzymatically, hydrolytically or oxidatively. The chitosan solution is then alkalized with agitation using aqueous hydroxides and/or their salts to attain a pH not lower than 7.0. The precipitated modified microcrystalline chitosan is highly pure and may be concentrated and dried according to known methods. Methods according to the invention also include methods by which an aqueous solution of chitosan is first alkalized using hydroxides and/or their salts to a pH not lower than 7.0. Then the precipitated microcrystalline chitosan is subjected to enzymatic or oxidative degradation to achieve a desired average molecular weight and polydispersity. The product is highly pure and may be concentrated and dried according to known methods.

1 - 15 . (canceled)  
     
     
         16 . A method for preparing modified microcrystalline chitosan, comprising the steps of: 
 alkalizing at vigorous agitation an acidic aqueous solution of chitosan (increased range of molecular weights and polydispersity) with an aqueous base to form a second solution having chitosan concentration of about 0.01-20 wt % and a pH of at least about 7.0;    degrading said chitosan in said second solution under conditions to achieve a desired molecular weight range and polydispersity, said solution having a concentration of at least about 0.001 wt % of chitosan; and    precipitating said modified microcrystalline chitosan.    
     
     
         17 . A method according to  claim 16 , wherein said degrading step uses an enzyme to degrade said chitosan.  
     
     
         18 . A method according to  claim 17 , wherein said enzyme is selected from the group consisting of cellulases, chitanases and xylanases.  
     
     
         19 . A method according to  claim 16 , wherein said degrading step uses an oxidative agent to degrade said chitosan.  
     
     
         20 . A method according to  claim 19 , wherein said oxidative agent is hydrogen peroxide or sodium perborate.  
     
     
         21 . A method according to  claim 16 , wherein said degrading step uses a hydrolytic agent to degrade said chitosan.  
     
     
         22 . A method according to  claim 21 , wherein said hydrolytic agent is hydrochloric acid or chloroacetic acid.  
     
     
         23 . A method according to  claim 16 , wherein said chitosan has a concentration in said aqueous acidic solution is between 0.1 to 2 wt %.  
     
     
         24 . A method according to  claim 16 , wherein said aqueous acidic solution of chitosan comprises an acid selected from the group consisting of acetic acid, lactic acid, citric acid and hydrochloric acid and a pH of ≦6.9.  
     
     
         25 . A method according to  claim 16 , wherein said alkalizing step uses a base selected from the group consisting of sodium hydroxide, potassium hydroxide and ammonium hydroxide.  
     
     
         26 . A method according to  claim 16 , wherein said alkalizing step uses a base selected from the group consisting of sodium carbonate, potassium carbonate and ammonium carbonate.  
     
     
         27 . A method according to  claim 18 , wherein said degrading step is carried out at a temperature ≧20° C. until enzyme deactivation at elevated temperature.  
     
     
         28 . A method according to  claim 27 , wherein said degrading step is carried out at a temperature of between about 30° C. and 60° C.  
     
     
         29 . A method according to  claim 21 , wherein said degrading step is carried out at a temperature ≧20° C.  
     
     
         30 . A method according to  claim 29 , wherein said degrading step is carried out at a temperature between about 40° C. and 80° C.  
     
     
         31 - 39 . (canceled)