Date of Award

1987

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

J. S. Godber

Abstract

The effects of frozen storage, formaldehyde addition and freeze-thawing cycles were determined using three finfish species from the Gulf of Mexico, spotted seatrout (Cynoscion nebulosus), black drum (Pogonias cromis) and mullet (Mugil cephalus). Frozen storage of spotted seatrout fillets at $-20\sp\circ$C for 6 weeks led to reductions in pH, water-binding capacity and solubility of salt-extractable proteins. SDS-Polyacrylamide gel electrophoretic examination of the salt-extractable proteins showed that as time of storage increased, aggregation of high-molecular weight components occurred. The addition of 300 ppm formaldehyde prior to frozen storage did not produce significant changes. However, muscles containing 500 ppm formaldehyde showed decreases in pH, water-binding capacity, solubility of salt-extractable proteins and extensive diminution of high-molecular weight proteins on electrophoretic gels after 6 weeks of storage. Frozen storage of black drum fillets at $-20\sp\circ$C for 6 weeks led to a loss in solubility of salt-extractable proteins, decrease in water-binding capacity and increase in expressible moisture. Electrophoretic gel patterns of salt-extractable proteins showed complete insolubilization of high-molecular weight proteins. Protein extractions using 4% SDS and 5% NaCl in 0.02 M NaHCO$\sb3$ (pH 7.2) with or without 5% 2-mercaptoethanol revealed that protein aggregation during frozen storage were due the formation of hydrogen, hydrophobic and disulfide bonds. The reduction of proteins in SDS solutions suggests that intermolecular covalent crosslinks could also be formed. Black drum and mullet muscles with to 3 freeze-thaw cycles (done by freezing at $-20\sp\circ$C for 24 hrs and thawing in a refrigerator at 4-5$\sp\circ$C overnight) did not show significant changes in protein properties. With 5 freeze-thaw cycles, an increase in expressible moisture and extensive reductions in salt-extractable protein, water-binding capacity and protein components on electrophoretic gels occurred. Differential protein extraction revealed that hydrophobic and disulfide bonds were involved during protein denaturation with increased freeze-thaw cycles. Elution profiles of salt-extractable proteins from spotted seatrout by high-performance gel permeation chromatography showed that low-molecular weight degradation products are formed during frozen storage. The solubility of these proteins during frozen storage decreased as formaldehyde concentration increased. No significant changes were observed with those from mullet with 0, 1 and 3 freeze-thaw cycles.

Pages

155

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