Low molecular weight chitosans--preparation by depolymerization with Aspergillus niger pectinase, and...

Area of Science:

• Biochemistry
• Polymer Science
• Materials Science

Background:

• Chitosan, a versatile biopolymer, exhibits properties influenced by its molecular weight and structure.
• Enzymatic modification offers a controlled method for altering chitosan characteristics.
• Understanding structural changes in low molecular weight chitosan (LMWC) is crucial for its applications.

Purpose of the Study:

• To investigate the enzymatic degradation of chitosan using pectinase from Aspergillus niger.
• To characterize the structural and physical properties of the resulting low molecular weight chitosans (LMWC).
• To determine the impact of thermal drying on the solubility and functionality of LMWC.

Main Methods:

• Enzymatic hydrolysis of chitosan solution with pectinase at pH 3.0 and 37°C.
• Molecular weight determination of LMWC.
• Analysis of structural changes using Circular Dichroism (CD) spectra, X-ray diffraction (XRD), Fourier-Transform Infrared (FT-IR) spectroscopy, and Carbon-13 Solid-State Nuclear Magnetic Resonance (CP-MAS 13C NMR).
• Assessment of solubility and functionality after thermal drying.

Main Results:

• Pectinase rapidly reduced chitosan viscosity, producing LMWC (5000-20,000 Da).
• CD spectra indicated reduced acetylated glucosamine units.
• XRD and CP-MAS 13C NMR revealed increased crystallinity and polymorphism in LMWC.
• Thermal drying led to structural alterations and an insoluble product.
• FT-IR and XRD confirmed no Schiff's base linkage or annealed polymorph formation.
• CP-MAS 13C NMR showed significant changes in LMWC chain conformations.

Conclusions:

• Enzymatic hydrolysis with pectinase effectively produces LMWC with altered structural properties.
• Thermal drying induces structural modifications in LMWC, leading to a loss of solubility and functionality.
• Changes in chain conformation are likely responsible for the observed insolubility of dried LMWC.