Dept. of Biological and Agricultural Engineering, Univ. of California, Davis, Davis, CA, USA.
J Food Sci. 2010 Oct;75(8):E508-15. doi: 10.1111/j.1750-3841.2010.01788.x. Epub 2010 Sep 20.
Effective means for controlled delivery of nutrients and nutraceuticals are needed. Whey protein-based gels, as a model system and as a potential delivery system, exhibit pH-dependent swelling when placed in aqueous solutions. Understanding the physics that govern gel swelling is thus important when designing gel-based delivery platforms. The extent of swelling over time was monitored gravimetrically. In addition to gravimetric measurements, magnetic resonance imaging (MRI) a real-time noninvasive imaging technique that quantified changes in geometry and water content of these gels was utilized. Heat-set whey protein gels were prepared at pH 7 and swelling was monitored in aqueous solutions with pH values of 2.5, 7, and 10. Changes in dimension over time, as characterized by the number of voxels in an image, were correlated to gravimetric measurements. Excellent correlations between mass uptake and volume change (R(2)= 0.99) were obtained for the gels in aqueous solutions at pH 7 and 10, but not for gels in the aqueous solution at pH 2.5. To provide insight into the mechanisms for water uptake, nuclear magnetic resonance (NMR) relaxation times were measured in independent experiments. The relaxation spectrum for the spin-spin relaxation time (T(2)) showed the presence of 3 proton pools for pH 7 and 10 trials and 4 proton pools for pH 2.5 trials. Results demonstrate that MRI and NMR relaxation measurements provided information about swelling in whey protein gels that can constitute a new means for investigating and developing effective delivery systems for foods.
需要有效的方法来控制营养物质和功能性食品的递送。乳清蛋白凝胶作为一种模型系统和潜在的递送系统，在置于水溶液中时会表现出 pH 依赖性溶胀。因此，在设计基于凝胶的递送平台时，了解控制凝胶溶胀的物理原理非常重要。通过重量法监测随时间的溶胀程度。除了重量法测量外，还利用磁共振成像（MRI）——一种实时的非侵入性成像技术，对这些凝胶的几何形状和含水量的变化进行定量。在 pH 7 下制备热凝乳清蛋白凝胶，并在 pH 值为 2.5、7 和 10 的水溶液中监测溶胀情况。通过图像中的体素数量来表征随时间的尺寸变化，与重量法测量结果相关联。在 pH 值为 7 和 10 的水溶液中，凝胶的质量吸收和体积变化之间（R(2)=0.99）存在极好的相关性，但在 pH 值为 2.5 的水溶液中凝胶不存在这种相关性。为了深入了解水吸收的机制，在独立实验中测量了核磁共振（NMR）弛豫时间。自旋-自旋弛豫时间（T(2)）的弛豫谱表明，pH 值为 7 和 10 的试验存在 3 个质子池，而 pH 值为 2.5 的试验存在 4 个质子池。结果表明，MRI 和 NMR 弛豫测量为乳清蛋白凝胶的溶胀提供了信息，这可以为研究和开发功能性食品的有效递送系统提供新的手段。
