Chemical and Functional Properties of Food Saccharides

(a)
(b)
© 2004 by CRC Press LLC
FIGURE 14.1 Schematic representation of the chemical structure of chitin (a) and chitosan (b).
in 0.1 M acetic acid. 3 Commercially produced chitosans are normally prepared by
alkaline deacetylation of chitin.
Several methods have been proposed and used for determining the degree of Nacetylation
of chitosans: IR, UV, gel permeation chromatography, colloid titration,
elemental analysis, dye adsorption, and acid–base titration methods. 3 These methods
have repeatedly been reported to be only partially quantitative and relatively cumbersome.
An enzymatic method based on complete hydrolysis of chitosan for determining
the fraction of N-acetylated units, F A, has been proposed, 4 in which quantification
of GlcNAc and GlcN was done either colorimetrically or by HPLC analysis.
Also, a similar method based on acid hydrolysis of the N-acetyl groups and detection
of acetic acid by HPLC analysis and UV spectrometry has been reported. 5 This
method is advantageous in that both chitosan and chitin (soluble and insoluble
material) can be analyzed. Proton NMR spectroscopy is a convenient and accurate
method for determining the chemical composition of chitosans, 6,7 and a typical
proton NMR spectrum used to determine F A is shown in Figure 14.2. NMR measurements
of aqueous solutions of chitosans are, however, limited to samples that
are soluble in the solvent, which limits the analysis to chitosans with F A values lower
than ca. 0.7 in aqueous solutions.