Method for producing chitin or chitosan

Abstract

A method is disclosed for improving the efficiency of producing chitin and chitosan, particularly biocompatible chitosan. Crustacean shells are maintained at a high temperature for a sufficient time to convert most of the chitin in the shells to an amorphous form. The shells are then rapidly cooled, for example by plunging into liquid nitrogen, so that most of the chitin in the shells remains in the amorphous form. These “quenched” shells are then deproteinized and demineralized to produce chitin. The chitin may be deacetylated to produce chitosan. High purity chitin or chitosan is thereby produced at a lower cost than has been possible using previous methods. Biocompatible chitosan produced by this process may be used for the delivery of cells or bioactive agents, or for other applications. It is believed that the heating followed by immediate quenching enhances the formation of chitin chains in an amorphous or a relaxed form, making them more susceptible to attack by acid or alkali during the subsequent treatment steps. Making the chitin amorphous allows the more efficient and economical production of chitosan, using lower quantities of chemicals such as hydrochloric acid and sodium hydroxide, thus making the entire production process both more economical and less polluting.

I claim:  
     
         1 . A process for preparing chitin-containing, cleaned crustacean shells for chitin production or for chitosan production, said process comprising the steps of: 
 (a) maintaining the shells at a temperature above the endotherm of the shells for a sufficient time to convert most of the chitin in the shells to an amorphous form; and    (b) cooling the shells from the maintained temperature to a lower temperature that is substantially below the endotherm for the shells, wherein the lower temperature and the rate of said cooling are both such that most of the chitin in the shells remains in the amorphous form at the lower temperature.    
     
     
         2 . A process as recited in  claim 1 , wherein said maintaining step comprises maintaining the shells at a temperature above about 78° C. for more than about 24 hours, and wherein said cooling step comprises transferring the shells immediately from the maintained temperature into liquid nitrogen.  
     
     
         3 . A process as recited in  claim 1 , wherein said maintaining step comprises maintaining the shells at a temperature above about 78° C. for more than about 24 hours, and wherein said cooling step comprises transferring the shells immediately from the maintained temperature into a liquid—dry ice bath.  
     
     
         4 . A process for producing chitin, said process comprising the steps of: 
 (a) preparing crustacean shells by the process recited in  claim 1;     (b) deproteinizing the prepared shells; and    (c) demineralizing the prepared shells;    whereby chitin is produced.    
     
     
         5 . A process as recited in  claim 4 , wherein said deproteinizing step comprises reacting the shells with aqueous sodium hydroxide and heat; and wherein said demineralizing step comprises reacting the shells with hydrochloric acid.  
     
     
         6 . Chitin produced by the process of  claim 5 .  
     
     
         7 . Chitin produced by the process of  claim 4 .  
     
     
         8 . A process for producing chitosan, said process comprising the steps of: 
 (a) producing chitin by the process recited in claim  4 ; and    (b) deacetylating the chitin;    whereby chitosan is produced.    
     
     
         9 . A process as recited in  claim 8 , wherein said deproteinizing step comprises reacting the shells with aqueous sodium hydroxide and heat; wherein said demineralizing step comprises reacting the shells with hydrochloric acid; and wherein said deacetylating step comprises reacting the chitin with sodium hydroxide and heat.  
     
     
         10 . Chitosan produced by the process of  claim 9 .  
     
     
         11 . Chitosan produced by the process of  claim 8 .  
     
     
         12 . A process as recited in  claim 8 , additionally comprising the step of purifying the chitosan by dialysis, so that the purified chitosan is biocompatible.  
     
     
         13 . Biocompatible chitosan produced by the process of claim  12 .