physicochemical and functional properties of crawfish chitosan as ...

ut the values were slightly higher than that (7.06% to 7.97%) reported by No and Meyers
(1995) for chitosan from crab and shrimp shell on a dry basis. This probably is due to the
presence of protein residues as mentioned by Rutherford and Austin (1978). Protein is bound by
covalent bonds forming stable complex with chitin and chitosan. Thus, it is very difficult to
achieve 100% deproteinization. Even with complete DP, nitrogen (7.06 to 7.97%; No et al.,
1995) is still remained as chitosan has the amino (-NH2) group.
4.4 Ash
Ash measurement is an indicator of the effectiveness of the demineralization (DM) step
for removal of calcium carbonate. Elimination of the demineralization resulted in products
having 31 – 36% ash (Bough et al., 1978). The ash content in chitosan is an important parameter.
Some residual ash of chitosans may affect their solubility, consequently contributing to lower
viscosity, or can affect other more important characteristics of the final product. A high quality
grade of chitosan should have less than 1% of ash content (No et al., 1995). An ash content of
less than 1% from crab chitosans has been reported by No and Meyers (1995). Table 3 also
shows the ash content of crawfish chitosans compared with that of the commercial crab
chitosans. Our crawfish chitosans contained less than 1% ash with a range of 0.2% to 0.9%,
except for DMPAC with 1.6%. Commercial chitosan products contained less than 2.0% ash.
4.5 Degree of Deacetylation
The degree of deacetylation of our crawfish chitosan samples ranged from 68% to 73%
with an average of 71% (Table 4). According to No and Meyers (1995), DD of chitosan ranges
from 56% to 99% with an average of 80%. Sample DCMPA (73%) had the highest DD, followed
by DMPCA, DMCPA and DPMCA (71%, 70%, and 68%, respectively). The FTIR absorption
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