Lowly
shrimp shells could yield jumbo benefits, researchers say
That's because the
shells of shrimp, crab and other crustaceans contain chitin, a
starchy, plastic-like compound that some scientists believe is
one of nature's most generous gifts.
Chitin is, after wood,
the most plentiful organic fiber on Earth. Researchers at the
Asian Institute of Technology in Bangkok say this resource
could be used to create everything from wonder drugs to
biodegradable plastics and crop enhancers for farmers.
Chitin can also be used
to heal wounds and as an agent in paper and textile
manufacturing, says Willem
F. Stevens, a researcher at the Asian Institute of
Technology. (
376 K/17 sec. AIFF
or WAV
sound)
|
|
Shrimp shell soup used to make chitin
|
|
To extract chitin, the
researchers create a purification bath for the shrimp shells.
A squirt of bacteria -- the same bacteria used in yogurt -- is
added to strip the protein out of the shells.
The chitin that's left
has some remarkable properities:
- It's antifungal and
antibacterial, but so easy on the skin that chitin
membranes are being tested as a treatment for serious burn
wounds.
- Made into a waxy
paper, chitin is nontoxic and quick to biodegrade.
- Chitin syrup, when
used to coat seeds, has been shown to improve crop yields
by helping the seeds resist fungus and repel insects.
Researchers say the
product's inherent stickiness also could prove valuable in:
- New blood-clotting
drugs for hemophiliacs.
- New sperm paralyzing
contraceptives.
- Fat-blocking drugs
for dieters.
Chitin and its more
refined cousin, chitosan, already are available in diet-pill
form.
"If you take
chitosan, you'll slim down even if you eat a lot,"
Stevens says.
|
|
Chitin powder
|
|
Thailand's Trang
Seafood, which is sponsoring the chitin study, would like to
find out if the discarded parts can be recycled into a
money-making resource. Researchers at the Asian Institute of
Technology believe that's possible, but that the startup costs
will be high.
"Well, I think
that's why our faculties are really looking for the
international connections," says Dr.
C. Kwei Lin, a researcher at the institute. "Maybe
foreigners would have the capital and be willing to invest in
us."
Already, Thailand's
tasty black tiger shrimp play a starring role in world
cuisine. Chitin experts are sure the shrimp will someday play
an equally important role in medicine and industry.
CHITIN
EXTRACTION
The
process begins when dump trucks offload crab chum onto the
factory’s concrete floor. Fresh crab chum smells like
steamed crabs, says Condon. Even when there are ten tons at
the factory, as long as the material does not sit for a few
days, there are no odor problems. A small skid steer loads the
material into a hopper. A series of augers delivers shells
into a 25-000 gallon holding tank. A dilute solution of
caustic soda with a pH of 13.5 dissolves any remaining flesh
and prevents further microbial activity or shell degradation.
From there, shells are pulled out of the tank with a drag
chain. The pieces go up a discharger snout and into a wash
process. They are then chopped into quarter-inch particle
sizes and conveyed into a mixing vessel, where they is treated
with hydrochloric acid to gasify the minerals. The shells go
through a sieve screen for solids separation and are washed
before entering another caustic solution with a slightly
elevated temperature to liquify proteins and produce chitin.
After another screening, the chitin is washed and put through
boiling lye to remove acetate from the molecule. It is now
chitosan. Acid is consumed in the reaction and the caustic
solution is recovered. The chitosan is then washed, dried,
ground, weighed and packaged for sale.
On a dry
weight basis, there is 12 percent yield in the process of
extracting chitin from crab chum. Of the remainder, about half
is gasified as CO2 and the rest is taken to Hurlock for
composting. Due to concerns about soluble salts, it is
processed separately from crab chum used for New Earth
Services’ premium Chesapeake Blue compost. “It’s in a
study pile,” says Condon. “Once it’s finished, we’ll
need to test for high conductivity.”
Lime is
another byproduct of the chitin process. “It’s not in a
form that is saleable,” says Condon. “I don’t know
whether we can compost it or process it into a form that can
be sold as lime.”
Next
season, New Earth Services will take as much crab chum as
possible at its chitin factory. Condon expects eventually to
pay a nominal fee for it. “It will be an incentive to the
industry to keep it clean and fresh, and then maybe we can
contract to be sure we have raw material. The tipping fee at
the composting site has generated tens of thousands of dollars
each year, but the price of chitin is $10,000 a ton.” His
research company, Venture Chemicals, has developed a new
application for chitin that should increase its market share.
Chitin also may become more popular if concern grows about the
toxicity of synthetic polymers used for removal of heavy
metals in municipal wastewater treatment.
What
remains to be seen is how crab chum will get to the chitin
factory. Condon would like to see cooperation among the state,
crab packers and his operation. “These guys are in the
middle of the boondocks, in remote areas driving on country
roads, and not everybody has a reliable vehicle to travel the
distance every day,” he says. “Funds could be made
available for pilot transportation projects, like a transfer
station for crab shells. The county brings garbage 40 miles
north; there’s no reason why it can’t provide similar
service for crab chum.” |
Chitin -
Chitosan 
