Water self-diffusion differentiates two protein-based burger matrices with contrasting sensory juiciness

Juiciness is a major sensory attribute of meat and plant-based protein foods, but bulk moisture content alone does not necessarily describe how water is organized within a food matrix. This study compared two structurally distinct commercial burger formulations-Angus beef and soy-based burgers-to determine whether time-domain nuclear magnetic resonance (TD-NMR) measurements of the pre-deformation water state distinguish matrices with contrasting sensory juiciness. Cooked burgers were characterized by TD-NMR relaxometry and apparent water self-diffusion, Cryo-SEM, texture profile analysis, cooking measurements, and trained sensory evaluation. At the independent parent-burger level, apparent water self-diffusion, D, was higher in beef than in soy-based burgers (1.030 ± 0.067 vs. 0.704 ± 0.070 × 10^-9 m² s^-1; n = 5 per formulation; p < 0.001), whereas mean long-T₂ did not differ significantly (p = 0.163). The exploratory D/long-T₂ ratio was also higher in beef (p = 0.026). Trained assessors rated beef as juicier than the soy-based burger (SJI 7.46 ± 1.41 vs. 5.00 ± 1.00; n = 13 paired assessors; p < 0.001), while initial moisture content did not differ significantly between formulations (p = 0.064). Cryo-SEM showed qualitative formulation-dependent differences in matrix morphology. TD-NMR and sensory measurements were obtained from separate experimental units; therefore, these results demonstrate parallel formulation-level differences and do not establish a within-sample correlation between D and sensory juiciness. Moreover, molecular self-diffusion is physically distinct from deformation-induced serum flow during mastication. The data support apparent water self-diffusion as a sensitive descriptor of the pre-deformation water state of these two matrices and motivate future studies coupling TD-NMR, mechanical serum release, and sensory measurements within the same independent samples.