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