Proteolytic degradation of fish flesh occurring at elevated temperatures is the
primary limitation for the commercial utilization of arrowtooth flounder (ATF).
Characterization of the autolytic activity of ATF muscle incubated at various pHs
and temperatures indicated the involvement of heat-activated proteinases active at
acidic and alkaline pHs. Further characterization of the proteinase extract from fish
muscle indicated the proteinase was more active at acidic pH than at alkaline pH in
hydrolysis of Z-Phe-Arg-NMec and all types of protein substrates tested. Based on
molecular weight and hydrolytic properties, activity peak separated on size exclusion
chromatography, or activity bands observed on activity-stained substrate gels were
presumed to be cathepsin L or like. A muscle proteinase showing similar hydrolytic
properties to a proteinase extract was purified to electrophoretic homogeneity and
subsequently confirmed by kinetic studies to be cathepsin L. Therefore, the results
clearly indicated that cathepsin L is primarily responsible for autolytic activity of
ATF muscle and surimi at the elevated temperatures.
Gelation of fish myofibrillar proteins, mainly myosin, is an important process
for surimi production. Elucidation of the gelation mechanism and the effect of
proteolysis on myosin provide information regarding protein interactions that
improve ATF product quality. Heat-induced changes in physicochemical properties
of myosin, free of endogenous proteinases, indicated myosin gelation consisted of
two processes, denaturation and aggregation. ATF myosin was shown to be
extremely sensitive to heat, resulting in denaturation at a lower temperature than
other fish myosins. Denaturation began at 25°C and was initiated by the unfolding of
the α-helical region. Following denaturation was the exposure of the hydrophobic
and sulfhydryl residues, which were subsequently involved in aggregation and the
gelation process. Changes in dynamic properties indicated ATF myosin formed a gel
in three different stages, as shown by the first increase in gel rigidity at 28°C,
followed by a decrease at 35°C and a second increase at 42°C.
A model system using ATF myosin and papain was developed to investigate
how proteolysis affects the heat-induced gelation of fish myosin. The addition of
papain decreased the onset temperature and the rate at which G' developed during
heating. DSC thermograms indicated papain significantly decreased the enthalpy
required to induce myosin denaturation with no significant changes in the onset or
the maximum temperature. Thermal denaturation kinetics indicated a decrease in
both the activation energy of the denaturation process and the denaturation rate of
myosin. Although myosin gels could be formed, structural disruption caused by
proteolysis, i.e., reduction in molecular size and loss in structural domain, resulted in
lowering of the gelling ability of myosin and rigidity of the formed gels. / Graduation date: 2000
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/26552 |
| Date | 02 June 1999 |
| Creators | Visessanguan, Wonnop |
| Contributors | An, Haejung |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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