Graduate Thesis Or Dissertation
 

Solubility and structure of fish myofibrillar proteins as affected by processing parameters

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/bn9998885

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  • The results of SDS-PAGE and densitometry indicated that a significant amount of myofibrillar proteins was lost during surimi processing. Microfiltration (MF) was utilized to recover insoluble particulate. The MF-recovered proteins showed highly functional properties in gel hardness, cohesiveness, color, and water retention ability. The soluble proteins concentrated by ultrafiltration (UF) possessed dark colors and strong odors. However, the use of UF demonstrated the possibility of recycling water in leaching systems. To reduce the loss of myofibrillar proteins during processing, the factors causing solubilization of myofibrillar proteins were investigated. Myosin and actin were highly soluble when their ionic strengths were substantially reduced. Salt concentrations of 0.25%, 0.5%, and 1.0% NaCl reduced the solubility of myosin and actin but did not remove sarcoplasmic proteins effectively. At 2.0% NaCl, severe loss of myosin, actin, α-tropomyosin, β-tropomyosin, and troponin-T was observed. At low water/meat ratio (2:1) with increased washing cycles and washing time, more sarcoplasmic proteins per unit of water were removed without a noticeable loss of myosin or actin. Myosin heavy chain (MHC) content, water retention ability, and whiteness of the washed mince were comparable to that at high water/meat ratio (4:1). Prolonged storage and elevated temperatures caused a severe proteolysis of myofibrillar proteins. The degraded proteins had higher solubility than their native myofibrillar proteins. MHC and actin degradation both showed a good correlation to protein solubility. The relationship between conformational changes and solubility of myofibrillar proteins was investigated using myosin as a model system. The results showed that adding salt or shifting pH from the isoelectric point of myosin caused an increased surface hydrophobicity and a decreased helix structure. A slightly increased sulfhydryl content was also observed. These conformational changes resulted in an increased solubility. At high salt concentration (>1.0 M), myosin regained its helix structure with a concomitant loss of solubility. The salting out effect was probably due to the dominant hydrophobic interaction among nonpolar amino acids residues.
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