physicochemical and functional properties of crawfish chitosan as ...

2.4 Factors Affecting Production of Chitosan
A number of processing factors affect chitosan's physicochemical characteristics.
1. Temperature of Deacetylation
Higher temperature tends to increase the degree of deacetylation but reduces molecular
size (Lusena and Rose, 1953). There is a substantially linear relationship between temperature
(plotted along the abscissa as 1/T in K) and the rate of deacetylation (plotted logarithmically
along the ordinate) (Peniston and Johnson, 1980).
2. Time of Deacetylation and Alkali Concentration
Wu and Bough (1978) suggested that deacetylation proceeds rapidly to about 68% during
the first 1hr in 50% NaOH solution at 100 o C. However, the reaction progresses gradually
thereafter reaching about 78% in 5 hr. Thus, alkali treatment beyond 2 hr does not deacetylate
chitin significantly, rather it degrades the molecular chain. In a concentration study with 35, 40,
and 50% NaOH (Bough et al., 1978), as alkali concentration decreased, rates of decrease in both
viscosity and molecular weight distribution also slowed. Bough et al. (1978) alluded that
chitosan deacetylated for 5 min with 50% NaOH at 145-150 o C had higher viscosities (1.7-16.4
fold) and molecular weight (1.1-1.8 fold) than did chitosans deacetylated for 15 min. Similarly,
decrease in viscosity with increased reaction time was shown and confirmed.
3. Effect of Treatment Conditions Applied in Chitin Isolation
Treatment conditions applied to chitosan isolation primarily affect viscosity of the
product than any other property. Madhavan and Nair (1974) reported that the use of HCl at
concentrations above 1.25N adversely affected the viscosity of the final chitosan product. In
addition, chitosan viscosity tends to decrease with increased time of demineralization (Moorjani
et al., 1975). On the other hand, Bough et al. (1978) found that deproteinization with 3% NaOH,
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