Effect of pH on the Preparation and Gelation Characteristics of Tilapia Surimi in Alkaline Solubilization/Isoelectric Precipitation
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Abstract:
Tilapia surimi (TS) was prepared by alkaline solubilization/isoelectric precipitation (pH-shift) in the pH range 10.5~12.5. On increasing the pH values, the protein recovery from TS significantly increased. However, when the pH value was increased from 11.5 to 12.5, the protein recovery only increased by 11.56%, while the alkali consumption increased by 77.65%. The increased pH values sharply decreased the ATPase activity of solubilized proteins (51.80→0%), but increased the surface hydrophobicity, indicating that increasing the pH values promoted the unfolding of myosin. The electrophoresis results showed that increasing the pH values did not cause significant differences in the composition of soluble protein at the isoelectric point (pI). As the pH value increased, the whiteness of TS first increased from 75.40 to 80.50, and then decreased to 76.20; the breaking force of the TS gel also decreased after an initial increase (290.00 → 335.20 → 278.80 g). Both the aforementioned results suggested that treatment under extreme alkaline conditions (pH >12.0) produced a negative effect on the quality of the TS gel. The electrophoresis results of the TS gel suggested that no significant differences were found in the protein compositions of gel proteins prepared at different pH values. In addition, no significant cross-linking occurred in myosin during the formation of the TS gel, indicating that the activity of endogenous transglutaminase (TGase) was very low compared to that in traditional surimi. This was probably due to the separation between TGase and TS at the pI during the second centrifugation.
