Low-resolution 1H NMR spectroscopy is a technique used to study molecular mobility in numerous food systems and therefore, it may be able to reveal matrix changes occurred during processing or storage. Egg yolk gelation induced by freezing-thawing processing is an undesired change for food processors due to the significant increase in viscosity that prevents effective mixing with other ingredients. The objective of this research was to develop a low-resolution 1H NMR technique to characterize the matrix mobility of fresh and freeze-thawed hen egg yolk, so this method can be used as a fast quantification tool. NMR analysis was conducted using the CPMG sequence to measure spin–spin relaxation times (T2) of proton pools representing yolk constituents. Three different experiments were conducted for this work. The first experiment was carried out to identify egg yolk components which allowed distinguishing 3–4 pools. The least mobile proton pool was assigned to proteins, protein–lipid and protein–water interactions, and the most mobile proton population to unbound water or exchangeable protein or lipid protons. The proton pools with intermediate mobility were assigned to lipids, lipid–protein and lipid–water interactions. A second experiment was conducted to study stability of fresh and gelled yolks up to 5 days of storage at 4°C. The results indicated that yolk matrix mobility changed across five days of refrigeration storage. They suggested that fresh yolk should be measured within the first 24 h after yolk separation. On the other hand, gelled yolks were shown to be stable during refrigeration storage. Thus, all fresh samples should be measured on the same day of preparation and immediately after thawing for gelled yolk. Robustness of the instrument and the methodology developed was assessed with a reproducibility test. The 1H NMR measurements of fresh yolk were consistent and highly reproducible. However, significant differences (p &lt; 0.05) were found within gelled yolk samples. This research demonstrated that low-resolution 1H NMR spectroscopy, a non-destructive technique, can identify yolk components, detect changes in the matrix and distinguish between the two systems with the same composition but different matrix structure. Furthermore, the methodology developed in this research holds promise for studying the changes that occur in hen egg yolk as a result of processing or storage, such as freeze–thaw gelation and may be applied to other foods systems.

Low-resolution 1H NMR as a reliable technique to study fresh and freeze-thawed hen egg yolk

253rd National Meeting (2017)

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