physicochemical and functional properties of crawfish chitosan as ...

%DD values. Thus, accurate determination of the degree of deacetylation of chitosan is needed.
DD values are not only highly dependent on the source and method of purification (No et al.,
1989) but also on the type of analytical methods employed, sample preparation, and type of
instrument used, and other conditions may influence the analysis of DD (Khan et al., 2002). The
anomaly of Sigma91 was maybe due to one of these different protocols in the manufacturing
process or the presence of impurities.
4.6 Molecular Weight (MW)
Molecular weight of chitosan varied with the sources and also the methods of
preparation. The MW of native chitin is usually larger than one million Daltons while
commercial chitosan products fall between 100,000 to 1,200,000 Daltons (Li et al., 1992). No
and Meyers (1995) reported an average MW of 0.12 ~ 1.5 X 10 6 Da., and the chitosan extracted
from the crawfish shell waste had a MW of 46,000 Da. The molecular weight of our crawfish
chitosan samples ranged from 674.49 to 10,596.62 Da. (Table 4). When chitosan process started
with decoloration (DC), the highest molecular weight (10,596.62 Da.) was shown. Acetone may
have tightened the molecular structure, which caused less accessible surface for the next steps.
Our crawfish chitosans were likely underwent more depolymerization which resulted in lower
molecular weight compared to the literature. In general and as previously mentioned, high
temperature, dissolved oxygen, and shear stress can cause degradation of chitosan.
4.7 Viscosity
The viscosity of chitosan solutions reported in the literature generally ranges from 60 to
780 cP (Alimuniar and Zainuddin, 1992; Anderson et al., 1978). These ranges of viscosity have
also been observed by Cho et al. (1998) with five commercially available chitosans.
Table 5 shows results of viscosity, solubility, and bulk density of our crawfish chitosans.
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