Magnetic Resonance Imaging (MRI) and Relaxation Spectrum Analysis as Methods to Investigate Swelling in Whey Protein Gels

Abstract

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.

Effect of pectin methyl esterase (PME) and CaCl2 infusion on the cell integrity of fresh-cut and frozen-thawed mangoes: An NMR relaxometry study

“…As the mobility of water is restricted, the H 1 protons in water display lower motional frequencies, increasing the efficiency of the spin-lattice energy transfer which results in shorter T 1 times (Hashemi et al, 2010;Hills, 1998). In a number of studies, formation of a gel matrix has been shown to dramatically decrease relaxation times (Dobies, Kusmia, & Jurga, 2005;Fyfe & Blazek, 1997;Knorgen, Arndt, Richter, Kuckling, & Schneider, 2000;Oztop, Rosenberg, Rosenberg, McCarthy, & McCarthy, 2010). Thus, it is safe to conclude that the decrease in T 1 times due to gel formation was high enough to compensate for the effect of increasing moisture content.…”

“…The variations in relaxation spectrum can be used as an indicator for numerous proton related changes within food systems such as an increase in water content, proton exchange between compartments and physiological incidences that causes new protons pools to emerge (Belton & Capozzi, 2011;Ersus et al, 2010;Hills, 1998;Oztop et al, 2010). For living cells, these proton pools refer to water compartments within the cell (Belton & Capozzi, 2011;Ersus et al, 2010).…”

Mathematical modeling of swelling in high moisture whey protein gels

“…Manganese chloride, a paramagnetic material, is used as a contrast agent in Magnetic Resonance Imaging experiments. The samples that incorporated manganese chloride were also used in a companion study (Oztop et al, 2010). Sodium azide (Sigma Chemical Co., St. Louis, MO, USA) was added at a concentration of 0.02% (w/w) to all protein solutions as an antimicrobial agent.…”

Mechanism of Water Dynamics in Hyaluronic Dermal Fillers Revealed by Nuclear Magnetic Resonance Relaxometry

“…[19][20][21][22][23][24][25][26][27] It consists of alternately placed monomers of D-glucuronic acid and N-acetyl-D-glucosamine linked by β-glycosidic bonds. [28,29] The water binding capacity, the time-scale and mechanism of water dynamics in the hyaluronic acid gels are factors determining the medical performance of dermal fillers. For medical use hyaluronic acid is often subjected to a cross-linking process that improves its rheological properties.…”