Study on phase separation and gelation in mixture solution of iota and kappa carrageenan
Lei Du1, Zhijing Liu2, Shuyun Wang2, Jingli Xie2, 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 

It is well known that the solutions of kappa carrageenan (KC) with additional salts form hard gels at relatively low gelation temperatures (Tg), on the other hand, those of iota carrageenan (IC) form soft gels at higher Tg. In many cases, the mixture solutions of KC and IC show two step increase of modulus on cooling in rheological measurements. This behavior is frequently assigned to micro phase separation1,2 but the mechanism of the phase separation and gelation are not sufficiently understood from a fundamental viewpoint.  In this study, the rheological and thermal properties of mixture solutions of KC and IC were systematically investigated by dynamic rheological measurements and DSC measurements with various concentration of KCl and carrageenans to clarify the micro phase separation and gelation mechanism.
In the dynamic rheological measurements, temperatures of two step increase of modulus were close to individual Tg for each solution of KC and IC with same concentration of KCl and total carrageen. DSC results also showed a congenial manner. These results suggested the gelations were independently occurred in the mixture solutions imprecating the micro phase separation. The change of concentration of cations and carrageenans in the each phases was simulated by using an apparatus where solutions of KC and IC were separated by dialysis membrane. The result indicated that each solution of KC an IC gathered KCl at Tg for each solution. By comparing the experimental results by the apparatus, the phase separation and gelation mechanism will be discussed. 

Reference:
1. L. Lundin, I.T.Norton., T.J. Foster, M.A.K. Williams, A.M. Hermansson, E. Bergstrom, phase separation in mixed carrageenan systems. Gums and stabilisers for the food industry 10, Royal Society of Chemistry, 2000: p. 14
2. T. Brenner, R. Tuvikene, A. Parker, S. Matsukawa, K. Nishinari, Rheology and structure of mixed kappa-carrageenan /iota-carrageenan gels Food Hydrocollids, 39, 272 - 279(2014).