Migration of cations between iota and kappa rich phases
Lei Du1, Jingli Xie2, Shuyun Wang2, Zhijing Liu2, Shingo Matsukawa1*
(1The Graduate School of Marine Science and Technology, Tokyo University of Marine Science and Technology, 108-0075, Konan 4-5-7, Minato-Ku, Tokyo, Japan.
2Department of Food Science and Technology, East China University of Science and Technology, 200237, No.130, Meilong Road, Xuhui District, Shanghai, China)
Tel: (+81) 03-5463-0581, Fax: +81-3-5463-0581, E-mail: matsukaw@kaiyodai.ac.jp

Phase separation occurred after the random coil-helix transition of in carrageenans, as one of the polysaccharide orders and the spatial arrangement[1]. And the formation of helix and aggregates were also influenced by cations. So cations and water redistribution were followed by phase separation. In this study, dependence of KCl on the rheological and thermal properties of mixed carrageenans was elaborated; furthermore, effect of gelation process and storage time on the cations distribution was also investigated by artificially separating two phase through dialysis membrane. As the mixed kappa-carrageenan (KC) and iota-carrageenan (IC) shows two steps gelation[2], so two critical increasing points of storage modulus (G’) and two phase transitional peaks in thermograph also occurred during cooling process, which suggested two conformational transitions proceed in the mixed carrageenan. In addition, phase transition temperature of IC is higher than KC, so K+ concentration in IC phase is higher than KC before KC starting to gel, while KC absorbed more K+ when it form gel because of specific to K+ ion. As for the storage time effect on the K+ distribution at 5oC, with storage time increasing, K+ concentration in KC started to increase after 1h, due to aggregate of KC growing. At lower temperature for long time, faster water mobility [3] and aggregates growth in KC phase to expel more water to IC phase, which could account for concentration of KC increased while IC decreased. All above results suggested that different microstructure of KC and IC phase in the mixture was formed. In conclusion, effect of gelation and phase separation on the cations distribution could be illustrated. 

Reference:
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2.	Parker, A., et al., Rheology and fracture of mixed ι- and κ-carrageenan gels: Two-step gelation. Carbohydrate Polymers, 1993. 20(4): p. 253-262.
3.	Zhao, Q.H., T. Brenner, and S. Matsukawa, Molecular mobility and microscopic structure changes in kappa-carrageenan solutions studied by gradient NMR. Carbohydrate Polymers, 2013. 95(1): p. 458-464.