physicochemical and functional properties of crawfish chitosan as ...
physicochemical and functional properties of crawfish chitosan as ...
physicochemical and functional properties of crawfish chitosan as ...
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2.5.4 Deacetylation<br />
A new process for treating chitin under high concentrations <strong>of</strong> sodium hydroxide with<br />
microwave energy w<strong>as</strong> proposed by Peniston <strong>and</strong> Johnson (1980) to accelerate the deacetylation<br />
<strong>of</strong> chitin within 18 min with 50% NaOH at a mean temperature under 80 o C. Chitin w<strong>as</strong><br />
deacetylated with concentrated aqueous NaOH in the presence <strong>of</strong> water-miscible organic<br />
solvents such <strong>as</strong> 2-propanol, 2-methyl-2-propanol or acetone (Batista <strong>and</strong> Roberts, 1990).<br />
Although it is difficult to prepare <strong>chitosan</strong> with a degree <strong>of</strong> deacetylation greater than<br />
90% without chain degradation, Mima et al. (1983) developed a method for preparation <strong>of</strong><br />
<strong>chitosan</strong> having a desired degree <strong>of</strong> deacetylation <strong>of</strong> up to 100%, without serious degradation <strong>of</strong><br />
the molecular chain. This w<strong>as</strong> achieved by intermittently w<strong>as</strong>hing the intermediate product in<br />
water two or more times during the alkali treatment for less than 5 hr in 47% NaOH at 110 o C.<br />
A simple <strong>and</strong> inexpensive technique for deacetylation <strong>of</strong> chitin h<strong>as</strong> been developed in<br />
which Alimuniar <strong>and</strong> Zainuddin (1992) produced <strong>chitosan</strong> by treatment <strong>of</strong> prawn chitin with<br />
strong sodium hydroxide at ambient temperature (30 o C) without heating in an inert atmosphere<br />
or without the addition <strong>of</strong> other additives to control the reaction. With 50% NaOH, the acid-<br />
soluble <strong>chitosan</strong> with 87% degree <strong>of</strong> deacetylation could be formed in a single day using 560 ml<br />
<strong>of</strong> the solution for 10 g <strong>of</strong> chitin, two days using 420 ml, three days using 280 ml <strong>and</strong> six days<br />
using 140 ml.<br />
For a large-scale preparation <strong>of</strong> <strong>chitosan</strong>, the process <strong>of</strong> deacetylation needs to be<br />
optimized. No et al. (2000) used autoclaving conditions (15 psi/121°C) to deacetylate chitin to<br />
prepare <strong>chitosan</strong> under different NaOH concentration <strong>and</strong> reaction times. Effective deacetylation<br />
w<strong>as</strong> achieved by treatment <strong>of</strong> chitin under an elevated temperature <strong>and</strong> pressure with 45% NaOH<br />
for 30 min with a solid: solvent ratio <strong>of</strong> 1:15. Treated <strong>chitosan</strong> showed similar nitrogen content,<br />
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