NMR Relaxation and Water Self-Diffusion Studies in Whey Protein Solutions and Gels

Abstract

The changes in water proton transverse relaxation behavior induced by aggregation of whey proteins are explained in terms of the simple molecular processes of diffusion and chemical exchange. The water self-diffusion coefficient was measured in whey protein solutions and gels by the pulsed field gradient NMR method. As expected, water self-diffusion was reduced with increased protein concentrations. Whatever the concentration, the water molecules were free to diffuse over distances varying from 15 to 47 mum. Water diffusion was constant over these distances, demonstrating that no restrictions were found to explain the water hindrance. The modification in protein structure by gelation induced a decrease in water diffusion. The effects of protein concentration on water diffusion are discussed and modeled. Two approaches were compared, the obstruction effect induced by a spherical particle and the cell model, which considered two water compartments with specific self-diffusion coefficients.

Novel Food-Safe Spin-Lattice Relaxation Time Calibration Samples for Use in Magnetic Resonance Sensor Development

“…The sample is a full fat milk powder which involve protein, lactose and fat, where fat has a comparable molecular size as the protein. As these component increased in volume (by virtue of the concentration increase), the nucleus rotation will be slower and this causes a faster decay of the relaxation time [9,11]. Figure 2 demonstrates the changes in the image contrast due to the changes in the inversion time (Ti) applied and the different milk concentration on each part of the letters (NTU) using the spine coil.…”

Investigations of food colloids by NMR and MRI

“…The water dependence on the protein concentration has been reported in casein and whey protein solution and gels [97,98]. In both systems the water diffusion was reduced with increased protein concentrations in solutions and gels.…”

Water-binding of protein particles

“…This is in agreement with the non-linear relationship described for native and thermally denatured bovine serum albumin solutions, and gels with concentrations ranging from 0 to 25% w/w. [104][105] Linear relationships were reported for whey protein solutions and gels with protein concentrations of 6 to 18% w/w [87] and 10 to 36% w/w, [33] which seems to correspond to the trend found here when only those concentration ranges were considered. Unexpectedly, the curve of the standard heated solutions was non-linear ( Fig.…”

“…Mono-exponential behaviour for WPI and whey protein concentrate gels with a protein concentration of 6 to 36% w/w has also been found by others. [33][87] [109] As expected, the L M -value of the gels decreased when the WPI concentration of the gel increased (Fig. 18B), because an increase in the protein content increases the total interaction with water and reduces the transverse relaxation time.…”