Water Structure Dynamics of Tofu Gels Analyzed by PFG-SE NMR and Dielectric Spectroscopy
川口, 翼 ,
斉藤, 宏伸 ,
喜多, 理王 ,
新屋敷, 直木 ,
八木原, 晋福崎, 稔
Proceedings of the School of Science of Tokai University
119 , 2015-03-20 , 東海大学理学部 , Tokai University. School of Science , 東海大学出版部
Tofu (soybean curd) is well known as a traditional food in Japan and Asia, and has attracted attention as a health food in western countries in recent years because of the high protein, low fat and low calorie. Tofu was made by heating soymilk and magnesium chloride as a coagulant. Coagulant concentration and heating time were respectively set from 0.4wt% to 0.6wt% and from 10 min to 60 min. The water dynamics of tofu gels were observed by Dielectric Spectroscopy (DS) as rotational diffusion and by Pulsed Field Gradient Spin Echo NMR(PFG-SE NMR) method as translational diffusion of water molecules. The hardness of tofu gel was dependent on the heating time and related to water structures characterized by dielectric relaxation time τ and relaxation strength ΔЄ .
On the other hand, the inhomogeneity of the gel structures was dependent on the coagulant concentration and discussed in terms of the fluctuation of water dynamics characterized by relaxation time broadening parameter β. In addition, translational diffusion of water molecules was observed by PFG-SE NMR method. A decrease in the diffusion coefficient of water molecules obtained with increasing coagulant concentration suggests a reduction of the free space for translational diffusion of water molecules. A correlation between the broadening parameter β and the diffusion coefficient D found by these complementary experimental techniques of DS and PFG-SE NMR characterizes inhomogeneity and tofugel structures in a wide time and space scale.