Abstract
ABSTRACTThe conformational changes of natural actomyosins prepared from fresh and freeze-thaw tilapia (Oreochromis niloticus) in the presence of Ca2+ or Mg2+ were investigated. The Ca2+-activated adenosine triphosphatase (Ca2+-ATPase) activities of actomyosins extracted from fresh and freeze-thaw fish were comparable (p > 0.05). The denaturation temperatures (Td) of actomyosins extracted from fresh fish were lower than those from freeze-thaw counterparts (p < 0.05). The addition of Ca2+ or Mg2+ reduced the Td of actomyosins. Ca2+ and Mg2+ enhanced protein aggregation at ≥ 40°C (p < 0.05). Based on the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) pattern, the myosin heavy chain (MHC) and actin bands tended to form large aggregates to a greater extent in the presence of 100mM Ca2+ or Mg2+. Ca2+ and Mg2+enhanced disulfide linkages and hydrophobic interactions among actomyosin molecules. The onset temperature of elastic modulus (G′) of both actomyosins was shifted to lower temperature as 100mM of Ca2+ or Mg2+ was added. Mg2+ at 20mM increased the breaking force of washed tilapia mince at 40°C. Our results revealed that the intrinsic properties of actomyosins extracted from fresh and frozen fish were distinct, and divalent ions Ca2+ or Mg2+ affected their gelation differently.
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