| Summary: | The relationship between the decomposition of trimethylamine
oxide in Pacific shrimp and shrimp meat quality was investigated to
evaluate the use of the trimethylamine oxide system as a quality
control indice.
Changes in the levels of trimethylamine oxide and its decomposition
products in whole shrimp stored on ice and in its derived raw
and cooked meat and in raw shrimp meat stored under refrigeration
(1-2°C) were investigated. The concentration dependency of the
decomposition of trimethylamine oxide to dimethylamine and formaldehyde
in frozen storage (-18°C) and the heat sensitivity of the
trimethylamine oxide decomposition systena was evaluated. A statistical relationship between amine and formaldehyde levels in whole
shrimp and raw and cooked meat stored under laboratory conditions
and obtained from commercial processing plants with flavor panel scores was developed.
Trimethylamine oxide levels decreased in a linear manner in
whole shrimp, and in the raw and cooked meat during iced storage.
This apparent disappearance was related to the washing action of
melting ice and its degradation to trimethylamine, dimethylamine
and formaldehyde. Levels of dimethylamine and formaldehyde
increased in a parallel manner during iced storage. Trimethylamine
levels increased steadily during the first four days of storage, followed
by rapid increase during the latter four days reflecting a
microbial out-growth.
Trimethylamine oxide levels in raw shrimp meat held at 1-2°C
decreased during the first four days of storage at a relatively slow
rate, followed by a sharp decline during the remainder of an eight
day storage period. Trimethylamine levels were shown to remain
relatively constant during the first four days of storage, followed
by a rapid increase in levels reflecting the decline of trimethylamine
oxide levels. Dimethylamine and formaldehyde levels increased
rapidly in a linear manner during the storage period.
Dimethylamine and formaldehyde levels in frozen raw shrimp
meat increased during storage (-18°C) in a linear manner. The rate
of dimethylamine formation was shown to depend upon initial trimethylamine
oxide levels and/or enzyme concentration. A rate
dependency on trimethylamine oxide for formaldehyde was not established. The presumably enzyme-catalyzed mechanism of
dimethylamine formation was found to be completely inactivated by
the exposure of the raw meat to water at 100°C for 15 seconds.
Flavor panel scores for cooked meat derived from whole shrimp
stored on ice declined in a linear manner over an eight day storage
period. Scores for these samples of shrimp meat and samples obtained
from commercial processing plants correlated well with
trimethylamine oxide, dimethylamine, and formaldehyde levels in
whole shrimp and derived raw and cooked meat. Trimethylamine
levels, indicative of microbial out-growth provided correlations
inferior to these indices.
The magnitude of change observed in trimethylamine oxide
levels accurately reflected flavor panel scores. The simplicity of
its determination supports its use in quality control practices. === Graduation date: 1976
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