The Effect Of The Konjac Glucomannan Deacetylation Process On Its Assembly Behavior In Single-phase Change And Multiple Phase Change Coupled Systems

Amorphophallus konjac K. Koch is a major commercial source of glucomannan, and konjac glucomannan (KGM), a component derived from the konjac tuber, is widely applied in fields of food, medicine and chemical industry. A small amount of acetyl (1acetyl among19main chain residues), ester bonded to the molecule of KGM, has a significant influence on the space-conformation and assembly behavior of the molecule. KGM and xanthan gum are the typical representatives of the synergies effect between two kinds of polysaccharides. In the present study, a series of KGM with different deacetylation degrees (DD) was obtained by homogeneous deacetylation reaction. The influence of acetyl content on KGM structure, rheological property, gelling property and film forming property was studied. The compatibility of deacetylated konjac glucomannan (DKGM) with Xanthan was also discussed. This paper attempted to investigate the subtle changing rules of the KGM properties during the deacetylation processing, which has been seldom considered.The main results indicated as follows:1. Na2CO3was selected as the acrtyl remover. DKGM samples with DD distributed from0.00%to75.49%were obtained via deacetylation modification at25℃. With the increase of the DD, the crystallinity and thermostability of the samples was increased, water absorption capacity was decreased, and the enzymolysis rate was slowed. More KGM could be added into food after its partly deacetylated reaction.2. The KGM solutions behaved as non-Newtonian fluid both before and after the deacetylation process. The increase of the DD enlarged the zero shear viscosity and enhanced the molecular interactions of KGM. However, the yelling stress of samples with different DD showed:low DD<native KGM<high DD samples. The DD of63.79%was the critical degree where1%KGM solution transformed from sol to gel. With the increase of DD, the storage modulus (G’) increased; the crossover frequency of G’and G "(loss modulus) reduced; and the Tm decreased. In the time sweep mode, the G’of samples with the highest DD continued to increase with the extension of the sweeping time. The responsivenesses of KGM solutions to stimulus enhanced after the deacetylation modification. The deacetylated KGM has the potential to be applied as intelligent gel materials.3. The KGM and Xanthan blended solutions also behaved as non-Newtonian fluid. The variation tendency of its rheological properties was similar to that of the KGM solutions. The synergistic interactions between KGM and Xanthan were enhanced by the uncomplete deacetylation of KGM. When the DD was beyond the sol-gel transition value of KGM, the synergistic interactions were weakened by the self-aggregating of KGM molecular chains.4. The hardnesss, chewiness and resilience of KGM gels increased, the springiness and cohesiveness changed slightly, and the adhesiveness kept decreasing with the decrease of the DD. These results indicated that deacetylation was in favor of the ordered self-assembly of KGM molecules. The network structure strength of the gels was enchanced, and the water binding capacity was declined. The synergistic gel forming effect of the KGM and Xanthan blended polysaccharides was reinforced by the deacetylation of KGM. The addition of Xanthan improved the water binding capacity of DKGM gels.5. The crystal structure and functional groups of DKGM films and freezing-dried powders were similar, but the thermostabilities were significantly different because of the diverse assembly structures and heat histories. Under heating condition, the solvent of KGM solutions evaporated, and the sol-gel transition of the KGM with less acetyl content happened earlier. The movement and assembly of the DKGM molecular chains are litimited, resulting in the increasing roughness of the microstructures, and the changing of mechanical properties, hygroscopicity, swelling capacity and water vapor permeability of the films. A moderate decrease of acetyl content could increase the water resistence, tensile strength, hygroscopicity and transmission of the KGM films. But, if the DD was too high, the assembly of the molecular chains would be delayed, and the uniformity and mechanical strength of the films would be reduced.6. The DKGM and Xanthan blended films possessed the maximum breaking strength, transparency and swelling ratio, the best compatibility, and the minimum hygroscopicity when the DD of KGM was about38.45%. The FT-IR data showed that there were strong hydrogen bonding interactions between KGM and Xanthan when the DD of KGM was low. Otherwise, the KGM molecular chains were more likely to be self clustered, which was unfavorable for film-forming. A phase separated morphology was ovserved by SEM. The crystallization peaks of the KGM molecular clusters were shown in XRD curves. The transparency decreased, and the thermostability increased.