physicochemical and functional properties of crawfish chitosan as ...

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