physicochemical and functional properties of crawfish chitosan as ...

methods are those of Hackman (1954), Anderson et al. (1978), Bough et al. (1978), and No et al.
(1989). But, reaction time varied with preparation methods from 30 min (No et al., 1989) to over
2 days (Hackman, 1954). However, Synowiecki et al. (1981) and Chen et al. (1994)
accomplished demineralization with 22% HCl and 6N HCl, respectively, at room temperature.
To avoid modifications such as depolymerization or deacetylation caused by harsh treatments,
Austin et al. (1981) suggested the use of mild acids such as ethylenediaminetetra-acetic acid
(EDTA) for decalcification.
Prolonged demineralization time for up to 24 hr results in only a very slight drop in the
ash content but can cause polymer degradation (Brzeski, 1982) or decreased viscosity (Moorjani
et al., 1975). Also it is important that the amount of acid be stoichimetrically equal to or greater
than all minerals present in the shells to ensure complete reaction (Johnson and Peniston, 1982;
Shahidi and Synowiecki, 1991).
2.5.3 Decoloration
When bleached chitin is desired, pigments can be removed with reagents. Hackman
(1954) obtained a cream-colored lobster chitin by washing with ethanol and ether, and Blumbeg
(1951) extracted pigments with cold sodium hypochloride solution, containing 0.5% available
chlorine, and Kamasastri (1961) with absolute acetone. Anderson (1978), Brine (1981), and
Brzeski (1982) also accomplished decoloration of chitin with chloroform, H2O2, and ethyl
acetate, respectively. No et al. (1989) prepared a white colored crawfish chitin by acetone
extraction, followed by bleaching with 0.315% sodium hypochlorite solution. However,
Moorjani et al. (1975) recommends not to bleach the material at any stage because the bleaching
process considerably reduces the viscosity of the final chitosan product.
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