Relaxation times and cross-relaxation nuclear magnetic resonance spectroscopy characterization of soy and wheat breads

摘要

A soy bread was developed by replacing 60% of the wheat flour with soy ingredients. Soy bread samples with and without almond powder (10% w/w) were characterized using proton nuclear magnetic resonance (NMR). T1 and T2 relaxation times were determinedand cross relaxation behavior was investigated during a 10 days storage period at refrigerated temperature. Results were compared to a conventional wheat bread. The NMR experiments were performed on a Bruker DMX 300MHz and run at room temperature. T1 and T2 values were acquired using inversion-recovery and CPMG sequences, respectively. Single exponential fitting were found to be adequate to properly fit the data points of all the samples. T2 values were found to be higher for the soy breads (about 6.5ms versus about 5 ms for the wheat sample) and remained unchanged for all the samples during the entire storage period. T1 values for wheat bread were found to be the highest and decreased continuously during the storage period; the soy bread product exhibited a decrease of T1 about 10% during the first day of storage and then remained constant for the rest of the study. Cross-relaxation spectroscopy was used to investigate the relevance of the solid like components in the samples, through the actual observation of the "liquid phase" protons. The soy samples were found to have a narrower line shape of the cross-relaxation spectra than wheat bread. For all the samples the cross-relaxation line shapes remained constant during storage. These results indicate that the highly homogeneously distributed water protons in soy bread have lower mobility throughout the storage period as compared to the wheat bread and therefore may impact storage stability.