Abstract: The physicochemical changes such as pH, moisture content, and chemical interaction among proteins, trichloroacetic acid solution (TCA)-soluble peptide, protein solubility, protein secondary structures and ultra- structure were measured to study the mechanism underlying protein changes during the processing and gelation of surimi from sea bass. The results showed that during the processing of surimi, pH was adjusted to approximately 7 by rising, and was reduced by chopping and heating at low temperature. Heating at 40 and 90 ℃ had no significant effect on the moisture content of surimi. Rinsing effectively inhibited protein degradation, and reduced TCA-soluble peptide by 83%. Chopping had no significant effect on TCA-soluble peptide content, protein solubility or sulfhydryl group content (P > 0.05). Heating at 40 ℃increased TCA-soluble peptide content by 68% due to the action of cathepsin. Ion bonds and hydrogen bonds continued to decrease during the whole process, and decreased significantly upon heating (P < 0.05). Hydrophobic interaction and disulfide bonds showed an upward trend, reaching the highest value upon heating at 90 ℃. Upon heating at 40 ℃, the maximum level of non-disulfide covalent bond was reached. The content of β-fold structure decreased by 13% after rinsing, the content of β-turn structure increased by 39%, while the contents of random coil and α-helix did not significant changed (P > 0.05). Chopping did not significantly affect the contents of β-fold, β-turn, random coil or α-helix. Upon heating at 40 ℃, the α-helix content decreased and the β-fold content increased by 8%. Upon heating at 90 ℃, the β-turn content increased by 36% (P < 0.05), the random coil content did not significantly changed. Correlation analysis showed that the chemical bonds between protein molecules were significantly correlated with the contents of α-helix and β-turn, but not with the contents of β-sheet and random coil. This study provides useful information for further study of the mechanism underlying the formation of surimi gel.

Key words: surimi gel; processing; physicochemical properties; secondary structure