Preparation and Molecular Characterization of Chitosans Obtained from Shrimp (Litopenaeus vannamei) Shells

Abstract

Four chitosan samples were prepared from shrimp shells without deproteination and decoloration steps, by a deacetylation process at 2 reaction times (2 and 4 h) and with/without using a reducing agent (R.A.). Variations in the physicochemical properties of the final products were analyzed. Viscosity average molecular weight (Mw) determinations demonstrated the protective action of the R.A. on the molecular oxidative degradation. Oppositely, an increase on the reaction time produced samples with low Mw. Deacetylation degrees (DDs) were chemically evaluated by the nitrogen content and by spectroscopic techniques as infrared and nuclear magnetic resonance. The existing differences in crystallinity were studied by X-ray diffraction. Differential scanning calorimetry and thermogravimetry were used to demonstrate the dehydration and thermal degradation processes of the different chitosans. A novel method from calorimetric profiles is presenting for DD determinations of chitosan, which achieved highly satisfactory results (linear fit and Pearson's correlation coefficient) and is proposed to be generally extended to complex curves application. Practical Application: A new thermal parameter from differential scanning calorimetry is proposed for deacetylation degree analysis that could be of advantageous usefulness against traditional methods in complex reactions applications. A complete study of Pearson's correlation coefficient performed over all the investigated physicochemical and thermal parameters clearly supports the use of the new thermal parameter. After validation, it could be normalized and automatized to be implanted as a short and easy quality control, analytical method with potential applications in the food and related industries.