Chapter 31
Protecting Crops and Wildlife with Chitin and Chitosan 1
M. L. Bade and R. L. Wick
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Department of Biology, Boston College, Chestnut Hill, MA 02167 Suburban Experiment Station, University of Massachusetts, Waltham, MA 02154
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Chitin and its deacetylation derivative chitosan show inhibitory activity against crop-damaging fungi and nematodes. A novel method for isolating chitin in forms that retain the high degree of native structure has been developed; its future large-scale employment promises formulation of less toxic pesticides to replace some of the more dangerous ones now in use. The ability of high grade chitosans to be cold cast into high tensile strength plastics has been demon strated. Plastics based on petrochemicals are not degraded in the environment within a reasonable time span and damage wildlife and fisheries. Chitosan -based plastics have desirable properties and are degradable; their degradation could become smoothly integrated into existing biogeochemical cycles. C h i t i n and chitosan a r e not widely regarded as b i o l o g i c a l l y a c t i v e ; c h i t i n , e s p e c i a l l y , i s considered t o be c h e m i c a l l y i n e r t and d i f f i c u l t t o h y d r o l y z e e v e n b y means o f s p e c i f i c e n z y m e s . I t h a s now b e e n shown (1) t h a t l a c k o f r e a c t i v i t y a n d l a c k o f p r e d i c t a b i l i t y o f performance i n subsequent r e a c t i o n s by p u r i f i e d c h i t i n and c h i t o s a n i s an a r t e f a c t o f i s o l a t i o n and can be a v o i d e d . Large-scale agri c u l t u r a l a n d o t h e r a p p l i c a t i o n s t h u s b e c o m e f e a s i b l e . Among t h e s e are formulation o f f u n g i c i d e s and nematocides of low t o x i c i t y , and m a n u f a c t u r e o f p l a s t i c t h a t combines h i g h t e n s i l e s t r e n g t h a n d good shelf l i f e with total biodegradability after discard. C h i t i n and Chitosan. The n a t u r a l p r o d u c t c h i t i n c o n s i s t s p r e d o m i n a n t l y o f u n b r a n c h e d c h a i n s o f β-(1,4)-linked N - a c e t y l g l u c o s a m i n e r e s i d u e s ( 2 ) . I t seems to be n e a r l y u b i q u i t o u s l y d i s t r i b u t e d i ni n v e r t e b r a t e exoskeletons (3). A n n u a l s y n t h e s i s i n t h e b i o s p h e r e i s e s t i m a t e d a t 100 b i l l i o n tons (4). An i m p o r t a n t d e r i v a t i v e , c h i t o s a n , r e s u l t s from d e a c e t y l a t i o n o f s u f f i c i e n t amine groups t o c o n v e r t v e r y i n s o l u b l e c h i t i n t o a m a t e r i a l s o l u b l e i n d i l u t e weak a c i d s u c h a s a c e t i c . 0097-6156/88/0380-0450$06.00/0 © 1988 American Chemical Society
In Biologically Active Natural Products; Cutler, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
31.
BADE & WICK
Protecting Crops and Wildlife with Chitin and Chitosan
Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on February 13, 2015 | http://pubs.acs.org Publication Date: November 28, 1988 | doi: 10.1021/bk-1988-0380.ch031
Since s o l u b i l i t y i s the c h i e f c r i t e r i o n f o r d i s t i n g u i s h i n g c h i t o s a n s f r o m p a r e n t c h i t i n , a number o f s u b s t a n c e s d i f f e r i n g i n d e g r e e and i n t e r n a l d i s t r i b u t i o n o f f r e e amine g r o u p s a r e d e s c r i b e d by t h e t e r m chitosan. Natural Sources. T y p i c a l l y , fibrous c h i t i n i n animal exoskeletons i s e m b e d d e d i n a p r o t e i n m a t r i x ; i t may a d d i t i o n a l l y b e a s s o c i a t e d with other materials. I n t h e m o s t common s o u r c e o f c h i t i n , s h e l l f i s h w a s t e , c h i t i n and i t s p r o t e i n m a t r i x a r e i n v e s t e d w i t h c r y s t a l l i n e c a l c i u m s a l t d e p o s i t s and l i p o i d c o l o r i n g m a t e r i a l s . Table I s h o w s t h e makeup o f Red c r a b w a s t e f r o m a c o m m e r c i a l c a n n e r y o p e r a t i o n i n Danvers, MA.
T a b l e I . C o m p o s i t i o n of
Red
Crab Waste w/w%
Component
45 20 20 trace 5 10
Water Edible protein Ca s a l t s Carotenes Structural protein Chitin
I t i s important to note that c h i t i n i n s i t u e x h i b i t s a high degree o f i n t e r n a l o r d e r p r i o r t o p o s s i b l e damage i n f l i c t e d d u r i n g i s o l a tion. T h i s i s e v i d e n t f r o m F i g u r e 1 w h i c h shows an e l e c t r o n m i c r o graph of d e c a l c i f i e d c r a b c l a w tendon i n w h i c h the p r o t e i n has not b e e n d i s t u r b e d and t h e c h i t i n i s l a r g e l y u n m o d i f i e d . F i b r i l s of
