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Purified tilapia myosin was digested with α-chymotrypsin and purified to obtain heavy meromyosin (HMM) and light meromyosin (LMM). The thermophysical properties of Tilapia myosin, HMM, and LMM were characterized. Constantly heated myosin, HMM, and LMM samples showed that aggregates began to form around 40 °C as evidenced by the increase of turbidity for all 3 samples (0.25 mg/mL). Beginning turbidity measurements showed differing levels of absorbance for each protein fragment with increasing absorbance values in the following order HMM, myosin, and LMM (0.0026, 0.0282, and 0.052, respectively). Differential scanning calorimetry showed 3 (17.5, 41.9, and 49.9 °C), 2 (43 and 67.1 °C), and 3 (40.4, 51.7, and 69 °C) major peaks for myosin, HMM, and LMM, respectively. Dynamic rheology measurements demonstrated crossover points, which are generally recognized as gelation point, 40.3 °C for myosin and 27 °C for HMM. The results shown for the thermally stable properties of tilapia myosin, HMM, and LMM showed clear evidence that they are all thermal stable at temperatures ranging from 10 °C to approximately 40 °C after which they all are completely denatured. The results also showed that the thermo stability of the myosin and its subfragments were greatly influenced by fish habitat temperature.

Species identification and protein quantification in surimi crabstick were achieved using sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE). When the Lowry and Kjeldahl protein determination methods were compared, the former showed more consistent results. Densitometric scanning of the gels was used for quantification of total fish protein as well as total egg white protein. The lower molecular weight proteins, 30 kDa and lower, proved to be the most useful in fish species identification as well as egg white protein addition. Using a combination of the myosin heavy chain band and the species-specific myosin light chain (Alaska pollock: 22.5 kDa; Pacific whiting: 24.4 kDa) proved the most accurate in calculating fish protein content of the crabstick sample, while for those samples that contained egg white, quantification was accomplished from the densitometric analysis of the overlapping bands of actin (45 kDa) from fish and ovalbumin from egg white. Lysozyme (14.3 kDa) proved to be a unique protein band in determining the presence of egg white when the content of dried egg white was equal to or exceeded 0.5% of the total weight of the final crabstick.

Purified Chinook salmon myosin was studied using sodium dodecylsulfate-polyacryamide gel electrophoresis and densitometric analysis to determine its purity (approximately 94%). Myosin subjected to a constant heating rate began to form aggregates at >24 °C as measured by turbidity at 320 nm. Conformational changes, as measured by surface hydrophobicity (S(o)), began at 18.5 °C and continued to increase up to 75 °C after which it decreased slightly. Total sulfhydryl (TSH) content remained steady from 18.5 to 50 °C after which point the TSH began to drop. Surface reactive sulfhydryl groups gradually increased as the temperature increased from 18.5 to 55 °C and then followed a similar trend as TSH decreased. Presumably disulfide bond started to be formed at around 50 to 55 °C. Differential scanning calorimetry showed 4 peaks, 3 endothermic (27.9, 36.0, 45.5 °C), and 1 exothermic (49.0 °C). Dynamic rheological measurements provided information concerning the gelation point of salmon myosin that was 31.1 °C as samples were heated at a rate of 2 °C/min.

Purified tilapia myosin was digested with α-chymotrypsin and purified to obtain heavy meromyosin (HMM) and light meromyosin (LMM). Biochemical properties of tilapia myosin, HMM, and LMM were characterized. Surface hydrophobicity (S(o) ) showed an increase for myosin and HMM between 30 and 40 °C and reached a plateau at 70 °C. LMM, in a small magnitude, also showed a continuous increase to 70 °C. Total sulfhydryl content (TSH) demonstrated that the SH residue content of HMM was nearly double that of LMM. Surface reactive sulfhydryl groups (SRSH) for myosin and HMM were relatively unchanged from 10 to 30 °C but increased from 30 to 50 °C. The exposure of buried hydrophobic and sulfhydryl groups of myosin and HMM increased as the myosin and HMM were constantly heated. However, the TSH and SRSH results indicated that the stability of LMM was likely due to its α-helix conformation. Reducing and nonreducing sodium dodecylsulfate-polyacryamide gel electrophoresis helped to understand the role of disulfide bonds in thermal aggregation of tilapia myosin, HMM, and LMM.

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