NMR studies of the gelation mechanism and molecular dynamics in agar solutions

Dai, Bona; Matsukawa, Shingo

doi:10.1016/j.foodhyd.2011.04.021

Cited by 49 publications

(21 citation statements)

References 13 publications

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“…A similar behavior was confirmed for gellan and agarose. 12,24 Finally, I kappa (0) at 20 1C was only approximately 10% of that at 50 1C, reflecting an ability of k-carrageenan to gel.…”

Section: Estimation Of the Hydrodynamic Screening Length Q Zhao And Smentioning

confidence: 95%

“…This decrease in I kappa (0) corresponds to a decrease in the solute k-carrageenan chains and an increase of the helical aggregates, which has strongly restricted molecular motion and a short relaxation time. 12,24 The changing tendency of the diffusion coefficient for k-carrageenan, D kappa , indicates that D kappa increased markedly as the temperature decreased below T sg (data not shown). The inclusion of the k-carrageenan chains into aggregates is thought to decrease the local friction through the hydrodynamic interaction and will lead to an increase in the molecular diffusion in the interspace.…”

Section: Estimation Of the Hydrodynamic Screening Length Q Zhao And Smentioning

confidence: 97%

“…At high temperature, I kappa (0) decreased slightly with decreasing temperature, which is most likely a result of an increase in the viscosity upon cooling, the relaxation time, T 1 and T 2 , values were thus decreased and led to a decrease in I kappa (0) according to Equation (2). At the sol-to-gel transition temperature T sg (28 1C, determined by falling ball method), 12,23 I kappa (0) decreased sharply. This decrease in I kappa (0) corresponds to a decrease in the solute k-carrageenan chains and an increase of the helical aggregates, which has strongly restricted molecular motion and a short relaxation time.…”

Section: Estimation Of the Hydrodynamic Screening Length Q Zhao And Smentioning

confidence: 98%

“…A schematic diagram of the pulse sequence can be found in the literature. 12 The temperature was controlled using a Bruker BVT-3200 (Bruker Biospin GmbH, Wissembourg, France) and was monitored using an optical fiber thermometer (Takaoka Electric Manufacturing Co., Tokyo, Japan) placed in the sample tube. Each measurement was carried out after waiting for 30 min to reach the thermal equilibrium.…”

Section: Nmr Measurementsmentioning

confidence: 99%

“…The formation of thick aggregated bundles and network structures by solute k-carrageenan chains is thought to result in an increase in the network mesh size. 12,16,24 The diffusion of pullulan is thought to be restricted by hydrodynamic interactions with the solute k-carrageenan chains as well as the network of aggregates. Therefore, the restriction became smaller as the solute k-carrageenan concentration decreased …”

Section: Estimation Of the Hydrodynamic Screening Length Q Zhao And Smentioning

confidence: 99%

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Estimation of the hydrodynamic screening length in κ-carrageenan solutions using NMR diffusion measurements

Zhao

Matsukawa

2012

Polym J

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We quantify the hydrodynamic screening length (n) in j-carrageenan solutions by observing restrictions on the diffusion of several pullulan probes, each with a different molecular weight (M w ). The diffusion coefficient of pullulan in a pure solvent (D pull,0 ) and a j-carrageenan solution (D pull ) were measured using a pulsed field gradient stimulated spin-echo 1 H nuclear magnetic resonance. The hydrodynamic radii (R H ) of the pullulan samples were determined using D pull,0 measured at 25 1C and the Stoke-Einstein equation. The echo signal intensity of j-carrageenan without a gradient, I kappa (0), decreased steeply at around the sol-to-gel transition temperature (T sg ), suggesting that the j-carrageenan chains formed helical aggregates at T sg diluting the solute j-carrageenan concentration. The ratio, D pull /D pull,0 , was less than 1, indicating that the mobility of pullulan was restricted by the j-carrageenan chains. Over the entire temperature range, pullulan with larger molecular size yielded more restrictions on the molecular mobility, and D pull /D pull,0 decreased as the M w of pullulan increased. Below T sg , D pull /D pull,0 increased as the temperature decreased. This behavior suggests that a decrease in the restriction degree by the j-carrageenan chains is concomitant with the formation of aggregates. To quantify the restriction degree, n was estimated at various temperatures using the relation D pull /D pull,0 ¼ exp( ÀR H /n). Polymer Journal ( Keywords: diffusion coefficient; gel; gradient NMR; hydrodynamic radius; hydrodynamic screening length; pullulan; k-carrageenan INTRODUCTIONThe diffusion of solutes in a gel matrix has an important role in applications such as the delivery of drugs and the encapsulation of fragrances. 1,2 NMR has proved to be a powerful technique for determining the dynamic and structural properties of food model systems 3 and the gelation process of polysaccharides. 4,5 NMR relaxation times give information about the tumbling motion of molecules in food hydrocolloid systems. The diffusion coefficients determined by pulsed-field-gradient NMR reflect the translational motion of molecules. The diffusion coefficient of solutes in a polymer matrix strongly depends on molecular weight, temperature, viscosity and the network structure of the diffusing matrix. Any factor that reduces the space delineated by the polymer chains will have an effect on the molecular mobility of the solute. In polysaccharide gels, the aggregation of polysaccharide chains can enlarge the diffusing space. Therefore, to understand the diffusion of molecules in a gel, it is important to understand the aggregation behavior.k-Carrageenan is a linear sulfated polysaccharide that is extracted from marine red algae. As shown in Figure 1, k-carrageenan comprises two galactose units: a-(1-3)-D-galactose-4-sulfate and b-(1-4)-3,6-anhydro-D-galactose. It is a gelling agent that has

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“…A similar behavior was confirmed for gellan and agarose. 12,24 Finally, I kappa (0) at 20 1C was only approximately 10% of that at 50 1C, reflecting an ability of k-carrageenan to gel.…”

Section: Estimation Of the Hydrodynamic Screening Length Q Zhao And Smentioning

confidence: 95%

Section: Estimation Of the Hydrodynamic Screening Length Q Zhao And Smentioning

confidence: 97%