Comparison of horse mackerel and tillapia surimi gel based on rheological and 1H NMR relaxation properties

Horse mackerel and tilapia surimi were subjected to six different heat and pressure treatments in order to compare gelation characteristics of easy- and difficult-setting gels, that is, temperature dependence, by observing rheological properties and microscopic molecular mobility. The stress-relaxation and proton spin-spin relaxation time (H-1 T-2) of water were measured for all treated gels. Horse mackerel gel demonstrated higher elasticity, large distribution of the stress-relaxation process, and smaller water H-1 T-2 than tilapia in both heat and pressure treatments. The water I H T-2 was steeply increased in the pressure treatment at around 294 MPa for both fishes. In contrast, the H-1 T-2 rarely changed in the heat treatment in spite of the considerable change in rheological properties. From the experimental results, it is considered that the gelation of horse mackerel (easy setting) surimi is induced by highly unfolding and re-aggregation of protein, which contributes to the formation of a strong network structure compared with tilapia in both heat and pressure treatments, and that pressure treatments hardly improve the gel strength of tilapia (difficult setting) surimi. The water H-1 T-2 measurement was used effectively in order to study gelation characteristics of easy- and difficult-setting fish through observing its molecular dynamics.