Water distribution in brine salted cod (Gadus morhua) and salmon (Salmo salar): a low-field 1H NMR study

Abstract

Low-field (LF) (1)H NMR T 2 relaxation measurements were used to study changes in water distribution in lean (Atlantic cod) and fatty (Atlantic salmon) fish during salting in 15% NaCl and 25% NaCl brines. The NMR data were treated by PCA, continuous distribution analysis, and biexponential fitting and compared with physicochemical data. Two main water pools were observed in unsalted fish, T 21, with relaxation times in the range 20-100 ms, and T 22, with relaxation times in the range 100-300 ms. Pronounced changes in T 2 relaxation data were observed during salting, revealing changes in the water properties. Salting in 15% brine lead to a shift toward longer relaxation times, reflecting increased water mobility, whereas, salting in saturated brines had the opposite effect. Water mobility changes were observed earlier in the salting process for cod compared to salmon. Good linear correlations ( F </= 0.05) were found between T 2 parameters and water holding capacity, centrifugation loss, water activity, and salt content in the liquid phase for all fish groups. Fillet pH and total weight changes correlated linearly with T 2 parameters for some of the fish groups.