Effect of salts on the structure-function relationships of sodium kappa-carrageenan
Carrageenans are sulfated marine polysaccharides used in a wide variety of food applications such as bodying, gelling, thickening and emulsion stabilization in water- and milk-based systems. They also find promising pharmaceutical usage due to antiinflammatory, anti-tumor and anti-coagulant activities, to name a few. Among them, kappa-carrageenan is favored owing to its desirable properties such as high gel strength and stability. Though the significance of cations on the structure-function relationships is well-documented, the role of anions is still elusive. This investigation aims at providing the pertinent details, especially in the presence of halide ions such as Cl-, Br- and I-. In this regard, sodium salts as well as sodium kappa-carrageenan have been chosen as the model systems. In addition, the effect of chaotropic salts urea and guanidinium chloride has been studied to understand their influence. Dynamic rheological measurements and melting properties were obtained for 1.5% and 2% w/w solutions in the presence of 0, 50, and 100 mM salts. X-ray diffraction has been carried out on oriented fibers to assess the extent of association among the carrageenan chains towards network formation. The addition of sodium chloride, sodium bromide or guanidinium chloride appears to promote aggregation among the carrageenan chains leading to increased elastic moduli, whereas urea has marginal effect. However, sodium iodide promotes soft gelling solutions as well as well-oriented and crystalline fibers. Furthermore, melting peak temperature and associated enthalpies are higher with sodium iodide than with the other salts, suggesting the important role of iodide ions in preventing the carrageenan chain aggregation leading to ordered networks. The outcome indeed aids in the enhanced utility of kappa-carrageenan, especially towards the design and development of novel functional materials such as carriers of bioactive compounds.
Janaswamy, Purdue University.
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