physicochemical and functional properties of crawfish chitosan as ...

treatment under severe conditions causes depolymerization and deacetylation. To obtain
uniformity in reaction, it is recommended to use relatively high ratios of solid to alkali solution
of 1:10 or 1:15-20 with proper agitation because a minimum ratio of 1:4 (w/v) of shell weight to
KOH solution, had only a minor effect on the DP efficiency of shells (No and Meyers, 1995).
Optimal conditions for deproteinization involve treatment of the crawfish shells with 3.5% (w/w)
NaOH solution for 2 hr at 65ºC with constant stirring and a solid to solvent ratio of 1:10 (w/v)
(No et al., 1989).
During the deproteinization process, foam formation can occur, but the foam is not as
brisk and intense as that produced during demineralization. Shahidi and Synowiecki (1991)
suggested that optimal deproteinization can be achieved using dilute potassium hydroxide
solution. Generally, if maximizing protein yield and quality is the objective, then protein
extraction before demineralization is recommended (Johnson and Peniston, 1982) or the pH of
the aqueous solution must be reduced to the isoelectric point of protein for precipitation (Green
and Mattick, 1979).
2.3.2 Demineralization
Demineralization is usually accomplished by extraction with dilute hydrochloric acid (up
to 10%) at room temperature with agitation to dissolve calcium carbonate as calcium chloride. A
wide variation of the demineralization process has been reported in the literature. The use of HCl
acid at higher concentration and also 90% formic acid to achieve demineralization has been
reported. Optimum demineralization is achieved by constant stirring of the dried ground crawfish
shell with 1N HCl for 30 min at ambient temperature and a solid to solvent ratio of 1:15 (w/v)
(No et al., 1989). The ash content of the demineralized shell is an indicator of the effectiveness
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