Raman Spectroscopic Study of Changes in Fish Actomyosin during Setting

Abstract

Actomyosins (AMs) isolated from tilapia, lemon sole, ling cod, and rock fish were heated at 40 degrees C, and structural changes in AMs were investigated using Raman spectroscopy to elucidate low-temperature gelling phenomenon, 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 residues occurring in long-time incubation at 40 degrees C, thereby forming hydrophobic interactions among AM molecules. In addition, the most frequent conformation in disulfide bonds was gauche-gauche-trans (g-g-t) form in the set gel. On the other hand, tilapia AM did not form a gel with heating at 40 degrees C, its alpha-helical structure in the myosin being far more stable than that of the other species. The heat resistance of the tight alpha-helix may prevent the gelation of tilapia AM. It is, therefore, likely that the unfolding of the alpha-helix of myosin is a prerequisite for gelation of AM during setting.

Rheological properties of fish actomyosin and pork actomyosin solutions

“…AM was extracted using a modified method to that described by Ogawa et al (1999). Fish or pork mince (100 g) was added 400 mL of 3.38 mM Na 2 HPO 4 -15.5 mM NaH 2 PO 4 buffer (pH 7.5) and homogenized for 2 min at <15°C.…”

“…The result was similar to that of Cofrades, Carechc, Carballo, and Jiménez Comenero (1993) who reported that viscosity decreased with higher ionic strength in both chicken and hacke AM. This was possibly due to the fact that an increase in salt concentration was accompanied by an increase in number of AM monomers, so that the smaller molecules resulted in smaller K values (Ogawa et al, 1999). Wakameda and Arai (1986) have demonstrated that myosin released upon incubation of carp myofibrils with 1.5-2.0 M KCl, which was the result of the selective detachment of F-actin by salt.…”

Vibrational Spectroscopy of Food and Food Products

“…186 A slow unfolding of a-helix, exposure of hydrophobic amino acids, and gauche-gauche-trans conformation of the disulfide bonds were observed during the low temperature (40°C) setting of actomyosins from various species of fish including lemon sole, ling cod and rock fish. 187 Actomyosin from tilapia, which did not form a gel by heating at 40°C, showed less unfolding of the helical structure, which was hypothesized as a prerequisite for gelation during setting. 187 Formation of formaldehyde in certain gadoid species has been suggested to play a role in the decreased solubility and altered texture of some fish after freezing or frozen storage.…”

“…187 Actomyosin from tilapia, which did not form a gel by heating at 40°C, showed less unfolding of the helical structure, which was hypothesized as a prerequisite for gelation during setting. 187 Formation of formaldehyde in certain gadoid species has been suggested to play a role in the decreased solubility and altered texture of some fish after freezing or frozen storage. Raman spectral analysis indicated a decrease in helical structure of cod myosin after treatment with 12 mM formaldehyde; involvement of hydrophobic interactions was also suggested by changes in the vibrational modes of aliphatic residues after addition of formaldehyde or frozen storage.…”

Rheological behavior of heat-induced actomyosin gels from yellowcheek carp and grass carp

“…Actomyosin was extracted according to the method of Ogawa et al [11] with some modifications. After thawing at 4°C for 3-4 h, fish mince was centrifuged at 8,000 rpm for 10 min at 4°C, and the supernatant was discarded.…”