Low-resolution sodium NMR in food biopolymers: The accessible information

Abstract

Measurements on the sodium/salt concentration in a food biopolymer have been conducted using a low-resolution NMR spectrometer tuned to the sodium nucleus. Whilst being a relatively insensitive technique, this approach is an environmentally friendly alternative to existing methods and provides the potential for additional information on the state of sodium in food biopolymers and products. Part of the sodium signal is missing when sodium is in the presence of charged polymeric material, such as gluten. It is proposed that the signal loss is due to some form of immobilisation of the sodium causing changes in either the T₁ or T₂ or both relaxation constants rendering part of the signal unable to be recorded. Further work is required to differentiate between the possible mechanisms. Specifically, calculating the missing fraction as a function of recycle delay time will help determine the responsible factor. A tentative model is proposed, which, based on the missing signal, demonstrates a method for calculating the sodium/salt added with the polymer (Sg), and a partitioning factor (P) of sodium between the solid (signal absent) and the aqueous (signal present) phases. A systematic experiment was conducted with a mixture of wheat gluten and salt to demonstrate the proposed method.