The aim of this study is to exploit a suitable chitosan extraction method from the chitin of indigenous
shrimp shells by employing different physicochemical treatments and to improve different bioactive properties of
this extracted chitosan (CS) by applying gamma radiation. Chitin was prepared from shrimp shell by pretreatment
(deproteination, demineralization and oxidation). Chitosan was extracted from chitin by eight different methods
varying different physicochemical parameters (reagent concentration, temperature and time) and assessed with
respect to the degree of deacetylation, requirement of time and reagents. The method where chitin was repeatedly
treated with 121°C for 30 min with 20 M NaOH, produced the highest degree of deacetylation (DD) value
(92%) as measured by potentiometric titration, with the least consumption of time and chemicals, and thus,
selected as the best suitable extraction method. For further quality improvement, chitosan with highest DD value
was irradiated with different doses (i.e., 5, 10, 15, 20 and 50 kGy) of gamma radiation from cobalt-60 gamma
irradiator. As the radiation dose was increased, the molecular weight of the wet irradiated chitosan, as measured
by the viscosimetric method, decreased from 1.16 × 105
to 1.786 × 103
, 1.518 × 103
, 1.134 × 103
, 1.046 × 103
and 8.23 × 102
dalton, respectively. The radiation treatment of chitosan samples increased the antimicrobial
activity signifi cantly in concentration dependent manner on both gram-positive (Staphylococcus aureus) and
gram-negative (Escherichia coli) bacteria, as determined by the well-diffusion method. Four to fi ve percent wet
chitosan treated with a radiation dose range of 5.0–10.0 kGy rendered the highest antimicrobial activity with
least energy and time consumption. Solubility, water binding capacity (WBC) and fat binding capacity (FBC)
also improved due to irradiation of chitosan.
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