LF H NMR T relaxation rate as affected by water addition, NaCl and pH in fresh, frozen and cooked minced hake.

Low-Field Nuclear Magnetic Resonance of proton transverse relaxation signal (T) was monitored in hake (Merluccius merluccius) mince with different thermal histories (fresh, frozen, cooked) as affected by pH, water and NaCl addition, and it was related to water holding capacity (WHC). Modifications of T signals were found in terms of changes in relaxation times and relative abundance of the relaxation components. The relaxation rate of the major component (1/T) increased significantly upon frozen storage or pH increase, whereas water or NaCl addition had the opposite effect. WHC decreased with freezing or water addition and increased with NaCl or basic pH; thus, T and WHC best correlated when each factor was analysed separately. Linearity found for pH and protein concentration with 1/T was consistent with chemical exchange being responsible for these changes. The significance of these results for technological situations where compositional and biochemical changes are occurring is discussed.