Dielectric properties and deacetylation of konjac glucomannan

• Published in: Current topics in nutraceuticals research 2015-11, Vol.13 (4), p.267
• Main Authors: Ji, Lei, Zhang, Tao, Feng, Dandan, Shao, Shuxiao, Xue, Yong, Xue, Changhu
• Format: Article
• Language: English
• Subjects: Acetylation; Aqueous solutions; Dielectric properties; Energy dissipation; Ethanol; Food; Heat; Methods; Spectrum analysis
• ISSN: 1540-7535; 2641-452X

The changes in the dielectric properties of konjac glucomannan (KGM) samples resulting from different degrees of deacetylation (DDs) were studied. Samples were obtained using a heterogeneous deacetylation method, yielding DDs of 0.00, 14.82, 30.10, 59.69, and two at 100.00%. The sample structure was determined by Fourier transform infrared spectroscopy, and ^sup 1^H nuclear magnetic resonance spectroscopy while viscoelasticity determined by rheological measurements. While the deacetylation reaction proceeded smoothly, the β-type configuration of the glycosidic bond remained unchanged. Furthermore, the storage modulus of full deacetylated samples showed a slight decrease up to 50° and then proceeded to increase steeply with rising temperature in the heating process. However, they remained constant in the cooling process, suggesting the formation of a thermoirreversible gel. The gelation behavior of KGM not only depended on DD, but also on the degree of excess basicity. Meanwhile, an open-ended coaxial probe technique was used to determine the dielectric properties of the KGM samples over a frequency range of 500-2500 MHz and for reaction temperatures of 25 and 90°. Both dielectric constant and loss factor were significantly affected, with the dielectric constant decreasing with increasing frequency and increasing with DD, loss factor, meanwhile, showed an inconsistency dependency. Finally, penetration depth decreased with increasing DD and the values at 915 MHz were higher than that at 2450 MHz.