Characterization of myosin, myoglobin, and phospholipids isolated from Pacific sardine (<i>Sadinops sagax</i>)
Myoglobin (Mb) was extracted from Pacific sardine and added to Pacific whiting surimi to measure its effects on protein gelation. The purity of Mb extract was determined by SDS-PAGE. Mb extracted using ethanol showed higher purity than Mb extract using ammonium sulfate. The addition of 0.2% Mb significantly reduced breaking force of Pacific whiting surimi gel. However, a synergistic effect of 1.0% Mb was observed with 1.0% beef plasma protein (BPP) to increase surimi gel strength. The highest storage modulus of gels was observed at 1.0% Mb addition, which corresponded with the non-fracture gel and also supported a synergistic interaction between 1.0% Mb and 1.0% BPP. Differential scanning calorimetry showed Mb addition might have affected myosin denaturation and aggregation.
Biochemical and conformational changes of purified sardine myosin were investigated at various pHs. The greatest myosin protein solubility was observed at pH 7 and remained constant up to pH 11. Three endothermic peaks were obtained for samples prepared at pH 7 and 10, while no peaks were shown for pH 2 samples, indicating chemical denaturation of myosin occurred before thermal treatment. The greatest Ca2+-ATPase activity was observed at pH 7, while no activity was observed between pH 2-5 and pH 11. Total sulfhydryl content showed low activity at pH 2.5-4 while the greatest measure was obtained for samples at pH 5.5. Surface hydrophobicity was not detected from pH 2.5 to 5.0 because of low protein solubility, thereafter, the content remained consistent through pH 11.
Phospholipids (PL) were extracted from Pacific sardine and added to Alaska pollock surimi to measure its effects on protein gelation. Sep-pak silica column was used with hexane and methanol for PL extraction. The purity of PL extract was determined by thin-layer chromatography and results demonstrated high purity of obtained PL extract. The PL fraction contained higher levels of unsaturated fatty acids than neutral lipids (NL) and total lipids (TL) fractions, respectively. Freeze-thaw process was conducted to rapidly induce changes to see the effects of phospholipids during a long period of storage. Storage modulus was affected by 1% PL addition compared to control during freeze-thaw study. However, PL did not affect to color of Alaska pollock surimi gel.