Study On Hydrophobic Regulatory Role Of Acetyl Group In The Sol-Gel Transition Of Konjac Glucomannan

Konjac Glucomannan is a high hydrophilic neutral polysaccharide and has no significant hydrophobic side groups. Work on driving forces of KGM gelation has not progressed significantly since the early studies of Meakaji. In the system of KGM sol-gel, excepting for hydrogen bonding, the evaluation of other sub-interactions can give a good explanation about its abnormal gelation behavior and unique properties. It also can broaden the field of potential applications of this intelligent hydrogel and can provide a new idea for scientific use of special resources-konjac in our country.In this study, a series of KGM with different degree of deacetylation without molecular degradation was obtained by heterogeneous deacetylation reaction. IR、XRD、DSC、GPC-MALLS are utilized to probe the influence of acetyl content on KGM structure. The relationship of DD and the KGM solubility is also discussed. The gelation and solution behavior of KGM with different DD are studied using dynamic viscoelastic measurement and fluorescent probes in order to identify and measure the hydrophobic interaction. The main results indicated as follows:1. Heterogeneous deacetylation reaction can be influenced by the kind and amount of alkali, ethanol concentration, temperature and reaction time; In the experimental conditions, deacetylation process followed the first-order kinetics and the apparent activation energy was 15.59 kJ/mol which is lower than 49.32 kJ/mol in homogeneous deacetylation, suggesting ethanol promoted the deacetylation.2. Excepting for the absorption peak assigned to the acetyl group decreasing with increase DD in IR spectras, the molecular main chain, thermal and crystallization characteristics of KGM with different DD have no obvious difference, mainly owing to the KGM granule swelling only a little and molecules extend inadequately to rearrange resulting in the effect of difference from DD on aggregate structure being not apparent.3. As increasing DD, the solubility of KGM showed exponential decrease. Lower temperature, stronger alkali, hydrogen bond cracking agent and salt-in salts can dissolve da-KGM effectively. 4. The conditions under which gelation can occure including KGM sample concentration, heating temperature, and heating time, became easier with increasing DD. The rheological behavior of known gelation mechanism of polysaccharide were compared to that of KGM with different DD, presuming hydrogen bonding and hydrophobic interactions play an important role in the gelation fo KGM, and inceasing DD promotes hydrophobic interactions. The presence of hydrophobic interactions of KGM was examined using the lyotropic series of salts.5. The presence of hydrophobic interactions of KGM is comfirmed by pyrene and 1,8-ANS fluorescence excitation and emission spectras. Altough KGM has no significant hydrophobic side group, the formation of hydrophobic domains is stronger. In the concentration from 0 to 10g/L, I₁/I₃ ratio declined from 1.75 to 1.25 in the pyrene fluorescence emission spectra.λ_max and fluorescence indensity occurred blue shif from 532nm to 502nm and from 130 a.u. to 220 a.u. in the 1,8-ANS fluorescence emission spectra, respectively. As increasing DD, KGM solutions did not show the enhancement of hydrophobic interaction, mainly due to the limitation of transparence. Before and afer warming, the CAC from the native KGM is 0.60g/L and 0.95g/L respectively, but this value from da-KGM（DD=32.58%）is 0.58g/L and 0.45g/L respectively. The addition of Na₂SO₄ and NaSCN make more significant influence on da-KGM compared with KGM. All phenomenon correlate well with the theory of salting in and out, indicating the difference of DD lead to the diversity of intramolecular and intermolecular forces to KGM solutions, namely, as increasing DD, compared with hydrogen bonding, the contribution ratio from hydrophobic interactions increases. 2mol/L urea destroyed hydrophobic microdomains from KGM and da-KGM to some extent.