RHEOLOGY OF GELS OF FREEZE-DRIED SURIMI O F TROUT (CYANOSCION-NOTHUS)AND TILAPIA (OROCHROMIS-NILOTICA)

Surimi was prepared from trout and tilapia and each one was divided in two batches. The first one was freeze-dried and the second one frozen . For the rheological tests in the frozen surimi the moisture/protein ratio was always adjusted to a constant 6:1 value by adding enough ice , and 2,5% NaCl was added to prepare sols. In the freeze-dried surimi the moisture/protein ratio was adjusted to 6:1, 5:1 and 4:1. Gels were obtained by two heating schedules: 90-degrees-C/15 min (direct) and 4 0-degrees-C/15 min - 90-degrees-C/15 min (setting). Shear stress and s hear strain at failure were measured in all gels by a torsion method. Results showed that in the direct process, frozen and freeze-dried sur imi gels prepared at the same moisture/protein ratio did not present s ignificative differences in the rheological parameters in tilapia. How ever, in trout, significantly lower values were observed in shear stra in after freeze-drying, Both, tilapia and trout, showed the setting ph enomena. The freeze-drying process decreased significantly this behavi our. In all gels, the lower the moisture/protein ratio values, the hig her shear stress and shear strain.