Self-Diffusion Coefficient of Water in Tofu Determined by Pulsed Field Gradient Nuclear Magnetic Resonance

Abstract

The self-diffusion coefficient of water in soybean protein dispersion and tofu was measured by pulsed field gradient (PFG) NMR. A soy protein isolate (SPI) dispersion (6 and 12%, w/w) in water, calcium cross-linked precipitate, and tofu were used for comparison. The self-diffusion coefficient of water (D) in the SPI dispersion, 2.23 x 10(-9) m2/s, was estimated lower than that of free water, 2.6 x 10(-9) m2/s at 25 degrees C, and decreased as the SPI concentration increased. It further decreased by the addition of calcium chloride, reflecting the obstruction effect induced by the precipitates in addition to the hydration and hydrodynamic interaction in the protein dispersion. The two water regions in tofu were interpreted by the two-site Kärger model: D1 and D2 of soft tofu were 2.26 (+/-0.11) x 10(-9) and 6.84 (+/-0.34) x 10(-11) m2/s, respectively. The relative amount of proton (water) was p1 = 0.98 and p2 = 0.02 at 100 ms of diffusion time. The self-diffusion coefficients of water decreased in pressed tofu, and their relative amounts of water changed to p1 = 0.93 and p2 = 0.07. It was suggested that D1 corresponded to obstructed water in the network structure and D2 corresponded to hydrated water on the surface layer of pores formed in the protein network of tofu. The pore sizes estimated from the diffusion length of obstructed water were 21.3 microm in soft tofu and 20.8 microm in pressed tofu. The removal of fat from pressed tofu led to a decrease in D2 from 6.26 (+/-0.31) x 10(-11) to 3.53 (+/-0.18) x 10(-11) m2/s, and the relative amount of hydrated water increased from 0.07 to 0.14, which indicated hydrophobic hydration.

Electrochemical analysis of a phospholipid phase transition

“…The surface diffusion constant (D) for DOPC in bilayers is reported as 3 · 10 À8 cm 2 s À1 [36]. The surface diffusion constant of water molecules is three orders of magnitude faster at $2 · 10 À5 cm 2 s À1 [37]. It therefore can be argued that the Debye element in the complex capacitance plots in Fig.…”

Static and pulsed field gradient nuclear magnetic resonance studies of water diffusion in protein matrices

“…28 The low-temperature activation energies of water dynamics in these models 28 are, however, about a factor of 3 larger than the value of 0.14 eV reported in early QENS work. 6 Static field gradient (SFG) and pulsed field gradient (PFG) NMR proved a versatile tool to investigate the translational diffusion of water on length scales of about 10 −8 -10 −5 m. 33 The potential of this method was exploited to determine self-diffusion coefficients D of water in protein matrices, 7, 34-37 in nano-and mesoporous solids, [38][39][40][41] in food matrices, [42][43][44][45][46] in hydrogels, 47 and in construction materials. 48,49 For the water diffusion in lysozyme, a crossover in the temperature-dependent diffusivity D(T) in the vicinity of 225 K was taken as evidence that a FS transition of the water results in a loss of flexibility of the protein.…”

MR imaging and diffusion studies of soaked rice

“…Furthermore, the exchange lifetime of the proton on the micelle surface was estimated to be about 8.0 ms, based on the longitudinal magnetization decay with the spin-lattice relaxation time (T 1 ). On the other hand, Hong and Lee (2006) reported that restricted diffusion of hydrated water and proton exchange were not observed on the surface layer of pores formed in the protein network of tofu, indicating a hydration effect through water-protein interactions, even with 8.6 T/m of gradient strength and 5.0 ms of diffusion time, due to the absence of barriers for diffusion and the fast proton exchange on the surface.…”

“…According to our previous studies, the effective self-diffusion coefficient of water and the cellular membrane permeability in yeast and chlorella were also successfully calculated (Cho et al, 2003;Suh et al, 2003), and the changes in the cellular membrane permeability of water were observed in yeast cells harvested at different growth stages and treated with different heating methods (Hong et al, 2004). The effective self-diffusion coefficient and restricted diffusion could be distinguished from diffusion according to the obstruction effect induced by the impenetrable slow-moving polymer molecules and the hydration effect through water-protein interactions on the surface layer of pores formed in the protein network of tofu (Hong & Lee, 2006).…”

“…Furthermore, MR imaging is not able to quantify water transport but only to visualize the internal structures. Recent advances in pulsed field gradient (PFG)-NMR techniques and theoretical developments make it possible to quantify the molecular diffusivities in plant and microbial cells (Cho et al, 2003;Hong, Suh, Yoon, Skirda, Volkov, & Lee, 2004;Suh et al, 2003;Zakhartchenko, Skirda, & Valiullin, 1998), and in food matrix (Hong & Lee, 2006).…”