Graduate Thesis Or Dissertation

 

Relation of the decomposition of trimethylamine oxide and the quality of Pacific shrimp (Pandalus jordani) Public Deposited

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  • 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.
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