A heat stable protease was identified as the cause of textural degradation in
cooked arrowtooth flounder (Atheresthes stomias) muscle. Maximum proteolytic
activity in the fish muscle was observed between 55°C and 60°C and myosin heavy
chain appeared to be the primary substrate for the enzyme. Degradation of this
myofibrillar protein at 55°C was extremely rapid and myosin heavy chain was
completely hydrolyzed to peptide fragments smaller than actin, while actin itself was
unaffected.
A single strand 32kD proteolytic enzyme was extracted from the muscle and
purified 125-fold. The enzyme was stable to freezing for up to 6 months. Activity of
the semi-purified enzyme at 55°C was optimal against casein between pH 6.0 and 7.0.
Sulfhydryl reagents p-chloromercuriphenylsulfonic acid, iodoacetate, iodoacetamide
and cystatin were effective in inhibiting enzyme activity in casein assays. The serine protease inhibitors phenylmethylsulfonylfluoride and trypsin-chymotrypsin inhibitor
appeared to activate enzyme activity against casein. Adenosine triphosphate was also
an activator.
Arrowtooth flounder was then considered as a raw material for surimi, since
the surimi process provides for repeated washing of the minced muscle and a final
mixing step during which inhibitory substances can be conveniently added.
Arrowtooth muscle was monitored at all stages of surimi production. There was no
evidence of myosin degradation on sodium dodecyl sulphate polyacrylamide
electrophoretic gels at any time during surimi production or during the preparation of
samples for testing. However, when the washed mince was incubated at 55°C, 12%
residual proteolytic activity was observed. This level was sufficient to degrade the
myosin component of surimi gels prepared from the control surimi to which no
inhibitors had been added. The food grade substances tested for proteolytic inhibition
were bovine blood plasma powder, egg white powder, whey protein concentrate,
carrageenan and crude α₂-macroglobulin. Addition of plasma and/or egg white
powders to control surimi resulted in a product that was comparable to pollock in
functional properties as measured by gel strength, expressible moisture and fold tests.
Electrophoretic comparison of surimi made with 1.0% or 2.0% plasma powder or egg
white with surimi produced with 0.1% or 0.2% α₂-macroglobulin suggested that the
plasma and egg white contributed gel enhancing effects in addition to protease
inhibition. Carrageenan was not effective as either a protease inhibitor or gel
enhancer. / Graduation date: 1992
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27202 |
| Date | 06 March 1992 |
| Creators | Wasson, Diana H. |
| Contributors | Selivonchick, Daniel P. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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