Raman spectroscopic study of changes in fish actomyosin during setting

Actomyosins (AMs) isolated from tilapia, lemon sole, ling cod, and rock fis h were heated at 40 degrees C, and structural changes in AMs were investiga ted using Raman spectroscopy to elucidate low-temperature gelling phenomeno n, that is, "setting", of surimi. The following conformational transitions were observed in lemon sole, ling cod, and rock fish gels during setting: a slow unfolding of alpha-helix and exposure of hydrophobic amino acid resid ues occurring in long-time incubation at 40 degrees C, thereby forming hydr ophobic interactions among AM molecules. In addition, the most frequent con formation in disulfide bonds was gauche-gauche-trans (g-g-t) form in the se t gel. On the other hand, tilapia AM did not form a gel with heating at 40 degrees%, its alpha-helical structure in the myosin being far more stable t han that of the other species. The heat resistance of the tight ct-helix ma y prevent the gelation of tilapia AM. It is, therefore, likely that the unf olding of the alpha-helix of myosin is a prerequisite for gelation of AM du ring setting.