Effect of Media Milling on Physical Characteristics and Enzymatic Hydrolysis of Chitin
Date Issued
2009
Date
2009
Author(s)
Lee, Yu-Hsuan
Abstract
Being abundant polysaccharides in nature and multi-applications such as biological, biocompatible and biodegradable functions, chitin and its derivatives are useful biopolymers and taken a lot of attentions by scientists and researchers in decades. They are present mainly in exoskeletons of invertebrates and the cell walls of fungi. The water insolubility constrains the application of chitin, however, the hydrolytic products of chitin such as N-acetyl chitooligosaccharides and chitooligosaccharides are water soluble and get lots of employments. The objective of this study was to investigate the influence of media milling on the particle sizes and physical properties of chitin as well as the enhancement of media milled chitin on the enzymatic hydrolysis. The volume mean diameter of purchased chitin was 224.50 ± 13.44 μm. It was processed by media mill to reduce the particle size to micron and submicron scales. Physical properties such as particle size distribution, pH, deacetylation, rheology and morphology were compared between the unmilled and milled chitin. Finally the yield of N-acetyl diglucosamine ((GlcNAc)2) was applied to explore the effect of milling on chitin hydrolysis. Chitin (5 or 12.5 g) was blended with 500 g deionized water to prepare a 1% or 2.5% slurry for media milling, where 0.8 mm YTZ (yttria-stabilized tetragonal zirconia) beads was selected as the milling media. After 30-, 60- and 120-min milling, the volume mean diameters were reduced to 76.08, 58.45 and 7.13 μm, respectively, for 1% solution and 82.40, 52.40 and 23.80 μm for 2.5% one. The particle size distribution and SEM morphology showed the presence of submicron chitin particles for 120-min milled products. The rheological studies of the milled chitin-suspension showed the viscosity was increased with the increase of concentration, and, however it decreased with increase of shear rate; i.e., the milled chitin-suspension appeared to be a shear-thinning fluid. The degree of deacetylation of chitin evaluated by FTIR was increased from 30.5 to 43% by media milling. The chitinase obtained from Streptomyces griseus was applied to proceed the hydrolysis of milled chitin. It showed that a longer milling product resulted in a higher yield of (GlcNAc)2 as the same hydrolytic duration was considered (8 hr). The yield of (GlcNAc)2 from unmilled chitin-suspension was 16.04%. For the hydrolysis of 30-, 60-, 90-min milled 1% chitin suspension, the yield of (GlcNAc)2 was 33.73, 34.09 and 41.35%, respectively; while for the hydrolysis of 30-, 60-, 120-min milled 2.5% chitin suspension, the yield of (GlcNAc)2 was 31.51, 34.15 and 44.28%.
Subjects
chitin
enzymatic hydrolysis
media milling
Streptomyces griseus
N-acetyl chitobiose
Type
thesis
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