Characterization of Chitin and Its Hydrolysis to GlcNAc and GlcN

Abstract

Proton NMR spectra of chitin dissolved in concentrated and deuterated hydrochloric acid (DCl) were found to be a simple and powerful method for identifying chitin from samples of biological origin. During the first hour after dissolving chitin in concentrated DCl (25 degrees C), insignificant de-N-acetylation occurred, meaning that the fraction of acetylated units (FA) of chitin could be determined. FA of demineralized shrimp shell samples treated with 1 M NaOH at 95 degrees C for 1-24 h were determined and were found to decrease linearly with time from 0.96 to 0.91 during the treatment with NaOH. Extrapolation to zero time suggested that chitin from shrimp shells has a FA of 0.96, that is, contains a small but significant fraction of de-N-acetylated units. Proton NMR spectra of chitin ( FA = 0.96) dissolved in concentrated DCl were obtained as a function of time until the samples were almost quantitatively hydrolyzed to the monomer glucosamine (GlcN). The initial phase of the reaction involves mainly depolymerization of the chitin chains, resulting in that almost 90% (molar fraction) of the chitin is converted to the monomer N-acetyl-glucosamine (GlcNAc).Thus, effective conversion of chitin to GlcNAc in concentrated acid is reported for the first time. GlcNAc is then further de-N-acetylated to GlcN. A new theoretical model was developed to simulate the experimental data of the kinetics of hydrolysis of chitin in concentrated acid. The model uses three different rate constants; two for the hydrolysis of the glycosidic linkages following an N-acetylated or a de-N-acetylated sugar unit and one for the de-N-acetylation reaction. The three rate constants were estimated by fitting model data to experimental results. The rate of hydrolysis of a glycosidic linkage following an N-acetylated unit was found to be 54 times higher as compared to the rate of de-N-acetylation and 115 times higher than the rate of hydrolysis of a glycosidic linkage following a de-N-acetylated unit. Two chitin samples with different F A values (0.96 and 0.70) were incubated in concentrated DCl until the samples were converted to the maximum yield of GlcNAc and the oligomer composition analyzed, showing that the maximum yield of GlcNAc was much higher when prepared from the chitin with the highest F A value.

Production of lipid from N‐acetylglucosamine by Cryptococcus curvatus

“…Absorbance at 637 nm was measured on a JASCO V-530 Model spectrophotometer. The NH þ 4 concentration was calculated based on a standard curve obtained with NH 4 Cl.…”

“…Currently, chitin is produced from commercial crab or shrimp processing waste, which are usually discarded to sea and result in high environmental pollution in many maritime states [2,3]. Hydrolysis of chitin by mineral acids or enzymes leads to the monomeric constituent GlcNAc [4]. As the chitin resource is abundant and seafood processing waste presents environmental problems, it is pivotal to explore GlcNAc as a feedstock for industrial biotechnology.…”

Turning polysaccharides into hydrophobic materials: a critical review. Part 2. Hemicelluloses, chitin/chitosan, starch, pectin and alginates

“…5). Although it has been proposed that, depending on the source, a variable, but always small, proportion of these structural units is deacetylated in natural chitin, this has never been proved unambiguously, with recent evidence pointing to the contrary (Einbu and Vårum 2008;Kurita 2006). The cohesive energy of chitin is higher than that of cellulose because of the additional and stronger hydrogen bonds between on the one hand, the OH and NH groups and, on the other, the NH and the carbonyl moieties.…”

Effects of chemical pretreatments on δ18O measurements, chemical composition, and morphology of chironomid head capsules

“…This alkaline treatment causes deproteination of insect cuticles (Schimmelmann et al 1986;Einbu and Vårum 2008). Because this process accelerates with increasing temperature, the effect of different temperatures and exposure times on head capsule composition was examined.…”