Relation between Rheological Properties and Protein Solubility of Heat-induced Gel from Frozen Surimi with Addition of Protein Powders

Ground meats (3% NaCl) composed of frozen surimi of arabesque greenling (AG) or walleye pollack (WP), both with and without the addition of 3% protein powders (albumen powder (Al), soybean protein powder (Sp), and Nacaseinate (C-Na)), were heated at 90 C for 30 mm. both with and without preheating at 25 C for several hours. The rheological properties of the heated gels were then measured with a rheometer throughout the preheating process. The heated gels were solubilized in various solvents, including 0.6 M NaCl (N), 1.5 similar to 8.0 M urea (U), and 2% mercaptoethanol (Me), and protein solubility was determined. 1) Direct heating of AG and WP and two-step heating of AG, both with and without the addition of individual protein powders, resulted in unset gels. 2) Two-step heating of WP, both with and without the addition of Al or Sp, resulted in a set gel, while the use of C-Na resulted in an unset gel. 3) The majority of the protein structure of unset gels was readily soluble in N+ 8.0 M U + Me, whereas the solubility of set gels in N+8.0 M U and N+8.0 M U+ Me was greatly reduced with the accumulation of an insoluble gel structure. 4) Protein solubility differed clearly between the set and unset gels. A large difference in the possible types of binding forces involved in both gel structures was therefore suggested.