In situ investigation of protein structure in Pacific whiting surimi and gels using Raman spectroscopy

Raman spectroscopy was used to study the in situ protein structure in raw and salted surimi from Pacific whiting, and in gels formed by setting (32 degrees C), cooking (86 degrees C) or setting followed by cooking. The set-cooked gel had a better gel strength and fold score than the gels which were only set or cooked. Large increases in relative intensity of a band near 530 cm(-1) in the cooked and set-cooked gels indicated changes in disulfide bond stretching or aliphatic chain vibrations. Involvement of hydrophobic interactions of aliphatic chains in salting, setting and cooking was inferred from the decreased intensity of a band near 2930 cm(-1) assigned to C-H stretching vibrations. Changes in a doublet near 850 and 830 cm(-1) suggested an increasing involvement of tyrosine residues as hydrogen bond donors in a non-polar environment after setting or setting-cooking, in contrast to increasing exposure to a polar environment in gels formed by cooking alone. Secondary structure estimation based on the amide I band indicated a change from predominantly alpha-helical structure in raw surimi to higher antiparallel beta-sheet and lower alpha-helical contents after setting and particularly during the kamaboko stage. (C) 1997 Published by Elsevier Science Ltd on behalf of the Canadian Institute of Food Science and Technology.