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In order to elucidate the molecular mechanism of transglutaminase-mediated myosin crosslinking, a fluorescent monodansylcadaverine (MDC) was incorporated into carp Cyprinus carpio myosin and the reactive Gln residues were analyzed by cyanogen bromide cleavage. The fluorescence was predominantly detected in a 10.5 kDa BrCN fragment, assumed to be located in subfragment 2 of the myosin heavy chain. Furthermore, lysyl endopeptidase digestion of the 10.5 kDa fragment revealed that MDC was specifically incorporated into the 520th Gln residue of the subfragment 2 domain. When meat paste prepared from frozen walleye pollack (Theragra chalcogramma) surimi was incubated with MDC, the fluorescence was mostly observed in a 16 kDa BrCN fragment and also slightly detected in other three bands. By digesting the 16 kDa fragment with lysyl endopeptidase, it was elucidated that MDC was incorporated specifically into Gln-520 of myosin subfragment 2, as also detected in carp. This domain around Gln-520 is likely to be a critical region for the formation of myosin heavy chain dimers that both fish species have in common. In walleye pollack, other reactive Gln residues are presumed to exist at the C-terminus of the light meromyosin. This slight difference may have a significant effect on the capacity of myosin to form tetramers or even larger multimers.

Tropomyosins from fish skeletal muscle show high amino acid sequence homology, although their thermal stability is clearly different among species. In order to determine the regions that are responsible for the stability of this protein, five synthetic peptides of 30mer were synthesized by Fmoc method, based on the sequence of walleye pollack Theragra chalcogramma fast skeletal muscle tropomyosin, namely, N terminal Metsup(1)-Lyssup(30), the variable region Aspsup(84)-Leusup(113), the middle region Valsup(128)-Alasup(157), the region containing the conservative Cys (Leusup(176)-Lyssup(205)), and C terminal Aspsup(255)-Ilesup(284). The thermal stability of these peptides was measured by circular dichroism and differential scanning calorimetry. The helical contents of these peptides were decreased in a temperature-dependent manner, although they showed no clear melting temperature, suggesting that the enthalpy necessary for the complete denaturation of these peptides was low. Peptides Aspsup(255)-Ilesup(284) and Aspsup(84)-Leusup(113) showed the highest and second highest alpha-helical contents, respectively, and the other peptides gave rise to lower alpha-helical contents.

Mince, salt-added surimi, and low-salt surimi prepared from Atlantic pollock had different protein, NaCl, and carbohydrate levels. Samples of these products were steamed, cooled, and coinoculated with Aeromonas hydrophila and Pseudomonas fragi. Jars containing modified atmosphere (MA)-stored samples were flushed so that initial headspace composition was 51% N2, 13% O2, and 36% CO2. These, and samples under air, were incubated at 5 and 13 degrees C. Headspace composition of sample jars determined throughout storage at 5 degrees C indicated that greater growth occurred on air-stored mince and low-salt surimi than on air-stored salt-added surimi, or on MA-stored samples. Colony counts of both species were appreciably reduced by the MA storage. In addition, the high salt level of salt-added surimi decreased growth of both species, although A. hydrophila was affected more than P. fragi. Results indicated that A. hydrophila was quite capable of competing with P. fragi on mince and low-salt surimi stored under air or MA at both 5 and 13 degrees C

Mince, salt-added surimi, and low-salt surimi prepared from Atlantic pollock had significantly (p<0.01) different protein and NaCl levels. These three products were steamed 16 min, cooled and inoculated with A. hydrophila , V. parahaemolyticus , or S. aureus . Samples inoculated with A. hydrophila were stored at 5, 13, and 25°C; all other samples were stored at 5 and 25°C. A. hydrophila grew well on the mince and low-salt surimi but not on the salt-added surimi stored for 5 d at 5°C, 36 h at 13°C and 27 h at 25°C. Populations on the mince and low-salt surimi increased log 3.0 CFU/g at 5 and 13°C, and log 5.0 CFU/g at 25°C. V. parahaemotyticus counts decreased slightly on all three products during 48 h storage at 5°C. At 25°C V. parahaemolyticus counts initially decreased on all three products but by 27 h rose at least log 2.0 MPN/g on the mince and salt-added surimi. Counts on the low-salt surimi rose

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