A Study On Sol-Gel/Conformational Transition Of κ-Carrageenan, Gellan Gum And Methylcellulose

Polysaccharides are on of the most abundant materials in nature.They are widely used both in food and industry. Gelation and bio-activity are the two dominating characters which influence its properties and thereby determine its usage as well as its proceeding and purifying. Furthermore, due to its wide application, especialy in complex system, it is of great importance to be aware of effects that the third component have on the comformation of polysaccharide. In this article,κ-carrageenan,de-acetyl gellan and methylcellulose was studied on their comformation.With a bio-dye methylene blue (MB) as probe, the UV-vis spectrums and thermal properties of MB-SDS-κ-CAR systems were studied at different SDS concentrations. As comparison, Rheology properties of SDS-κ-CAR systems were also investigated. Two modes were identified for the effects of SDS with various concentrations on the sol-gel transition ofκ-CAR: at lower concentration (c≤5mM), the start of sol-gel transition was promoted slightly by a weak salt-out effect, whereas at higher concentration (c>5mM), SDS aggregated or formed micelles, then significantly influenced the aggregation and gel formation ofκ-CAR by decreasing the temperature of the transition. The types and mechanisms of the interactions betweenκ-CAR and SDS were discussed in the present paper. And competition for counter-ion, electrostatic repulsion and hydrophobic interaction were suggested to explain the effects of SDS on the sol-gel transition ofκ-CAR.Based on determination of conductivity and diffusion coefficient, the coil-helix transition of gellan gum was studied using electrochemistry measurement in solutions with low ionic strength. DPE/Do which was the ratio of diffusion coefficent of K+ in gellan solution to that in KCl with equivalent K+ concentration showed a change of charge density along gellan molecular chains within 15-22℃, indicating a sol-gel transition occures in that temperature range. The difference of electrochemical behaviors betweenκ-carrageenan solution and gellan gum solution was also discussed.Attempts of studying the sol-gel transition of methylcellulose was made by eletrochemical measurement via a membrane-cage method. Result showed that component of menbrane as well as MB adsorption on the membrane made it complication to identify the sol-gel transition temperture. However, with this attempt, further study on MC might take place.