Abstract
Chitin-glucan complex (CGC) is a copolymer composed of chitin and glucan moieties extracted from the cell-walls of several yeasts and fungi. Despite its proven valuable properties, that include antibacterial, antioxidant and anticancer activity, the utilization of CGC in many applications is hindered by its insolubility in water and most solvents. In this study, NaOH/urea solvent systems were used for the first time for solubilization of CGC extracted from the yeast Komagataella pastoris. Different NaOH/urea ratios (6:8, 8:4 and 11:4 (w/w), respectively) were used to obtain aqueous solutions using a freeze/thaw procedure. There was an overall solubilization of 63–68%, with the highest solubilization rate obtained for the highest tested urea concentration (8 wt%). The regenerated polymer, obtained by dialysis of the alkali solutions followed by lyophilization, formed porous macrostructures characterized by a chemical composition similar to that of the starting co-polymer, although the acetylation degree decreased from 61.3% to 33.9–50.6%, indicating that chitin was converted into chitosan, yielding chitosan-glucan complex (ChGC). Consistent with this, there was a reduction of the crystallinity index and thermal degradation temperature. Given these results, this study reports a simple and green procedure to solubilize CGC and obtain aqueous ChGC solutions that can be processed as novel biomaterials.
Highlights
Chitin-glucan complex (CGC), a copolymer composed of chitin (N-acetyl-D-glucosamine polymer) and glucan moieties linked through β-(1,3) and β-(1,6) glycosidic linkages [1,2], is the main component of the inner cell wall of yeasts and fungi, contributing for the stiffness and stability of the cells [1,3]
Different procedures were adopted for chitin and cellulose solubilisation, namely, the initial polymer content, the number of freeze-thaw cycles and the exposure time to the solvent at low temperature, which have probably influenced the reported results. These results demonstrate that the tested NaOH/urea solvent systems were suitable to achieve high CGC solubilization, yielding solutions with polymer concentrations of 12.9 ± 1.1 wt% and 13.8 ± 0.2 wt% (Table 1)
In the case of chitin solutions, at low concentrations (0.5 and 1%) both mincordeualsiedhatvoe1.d5i%ff,earennatlovgaoluuseswaitthfrtheqeureensucylts1obHtzainwehdicfhoriCs GcoCnssoisltuetniot nws,itahcarodssi-luovteersoisluotbiosenr.vOedncaet caofnrecqeunternactyiobneilsowinc1rHeazs.ed to 1.5%, analogous with the results obtained for CGC solutions, a crossover is observed at a frequency below 1 Hz
Summary
Chitin-glucan complex (CGC), a copolymer composed of chitin (N-acetyl-D-glucosamine polymer) and glucan (glucose homopolymer) moieties linked through β-(1,3) and β-(1,6) glycosidic linkages [1,2], is the main component of the inner cell wall of yeasts and fungi, contributing for the stiffness and stability of the cells [1,3]. It was reported that low temperature steps (below freezing point of the solvent system) plays an important role in the solubilization process At such low temperatures, the hydrated alkali component disrupts the polymer chain matrix by breaking the hydrogen bonds and allowing the formation of new ones. The CGC was regenerated from such solutions and the resulting polymers were characterized in terms of acetylation degree, structural and thermal properties
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