Introduction: There is an expanding market for surimi in the world, and much interest in surimi throughout the seafood and food industry by the rapid growth in popularity of surimi-based products. This interest justifies an investigation into the applicability of freshwater fish species such as Silver carp, as an alternative fish resource, for surimi and surimi based products. Rheology concerns the flow and deformation of substances and, in particular, to their behavior in the transient area between solids and fluids. Moreover, rheology attempts to define a relationship between the stress acting on a given material and the resulting deformation and/or flow that takes place. Rheological properties are determined by measuring force and deformation as a function of time. Rheological evaluation is a useful technique for gathering information on the textural characteristics of surimi and kamaboko. It describes the surimi dynamic characteristics in the form of storage modulus (G′), loss modulus (G″), and phase angle (δ).
Materials and methods: Whole Silver carp fish were gutted and the head removed, Fillets were minced by a meat mincer with a mesh size of 3 mm, then mince washed one, two and three times at ratio of 1:3 and 1:2 (mince: water) and dewatered. The mince was turned into surimi in a food processor operated for 2 min. salt (2%) was sprinkled over the mince. Ice water was also sprinkled over the mince to adjust the moisture content of the paste to 80 mL/ 100 g.
Dynamic tests using a rheometer (MCR-301, Anton Paar- Germany) were carried out on the surimi gel after setting. The region of linear viscoelasticity of the surimi paste was determined by both stress and frequency sweep tests. The thermorheological behavior of Silver carp surimi was evaluated using a temperature sweep test and reported using sol-gel transition thermographs. The stress of 100 Pa was considered as the stress and the frequency of 1 Hz was considered as the frequency in the frequency sweep test, then Temperature sweep test involved heating the surimi samples from 10 to 90°C. Also Crip-recovery test was performed on the surimi in 300 seconds.
Results & discussion: Rheological tests: Frequency sweep, Stress sweep and Temperature sweep graphs were relatively similar and in all samples affected by H2O2 and the control sample, the lowest value of G' was recorded between 50 and 52°C. Then, with increasing temperature from 52 to 62°C, the curve G' increased and the curve was stable at temperatures up to 80°C. Changes in the G' graphs can be attributed to the process of forming the gel by heating. Changes in the G" graph showed a similar trend with G’. In the creep-recovery test, the lowest and most strain were belonged to the control and sample 5 (1% H2O2, 1: 2, twice washing). Studying the figure of Creep-recovery test showed the samples affected by H2O2 had more resistance against applied stress in compression with control sample which expressed the effect of H2O2 on creating more and effective covalence cross-linking resulting more stable and constant gel network. During Surimi's heating, there are several reactions that involve various mechanisms, such as protein gelation. About Surimi, the observed macroscopic changes are related to the effect of temperature on proteins. The presence of H2O2 during the washing process did not have a significant negative effect on rheological properties of Surimi.