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Evaluation of factors affecting, and methods for extending, the shelf-life of packaged seafoods

thesis
posted on 2023-05-27, 17:12 authored by Statham, Jo (Jo Anne)
Vacuum packaging of fish results in minimal shelf-life extension due to the influence of the biochemical characteristics of fish muscle, such as the presence of trimethylamine oxide (an electron acceptor), low glycogen reserves and high ultimate pH. It is difficult to inhibit Gram negative spoilage bacteria without the addition of some form of preservative. Potassium sorbate effectively slowed microbial growth in scallops (Pecten fumata) when used in conjunction with vacuum packaging. Shelf-lives of 21-28 days at 4°c were obtained. Inhibition of spoilage for extended periods and temperature abuse of sorbate treated scallops did not appear to increase the risk of spore germination and toxin production by Clostridium botulinum Types A, B, E and F. Toxin was produced by Type A at 27°c, but only after the scallops had deteriorated beyond acceptability. No toxin was produced at 4°c or 10°c. The effect of K-sorbate on the shelf-life of blue grenadier (Macruronus novaezelandiae) fillets was less dramatic. Inconsistent results could be expected due to the variable properties of the fish flesh. pH is an important factor, as it affects the proportion of sorbic acid present in the undissociated state. Modified atmosphere storage (using 100% co2) at 4°C resulted in a shelf-life of 16 days for trevalla (Hyperoglyphe porosa) and 22 days for scallops. The effect of co2 was to slow bacterial growth and select a flora dominated by lactic acid bacteria. A combination of potassium sorbate, polyphosphate and 100% co2 was more effective in extending the shelf-life of morwong (Nemadactylus macropterus) than either treatment alone, however the fillets dropped below borderline acceptability after 13 days. Inhibition of bacterial growth or the complete elimination of bacteria showed that the maximum shelf-life of seafoods is restricted by non-microbial factors. The shelf-life of sterile mullet and trumpeter stored at 4°c was limited by nucleotide degradation and oxidation of fats, and was only marginally longer than for fish spoiling in the presence of bacteria. Antimicrobial activity of weak organic acids is considered to be pH dependent, the effect being reduced with increasing pH. However, potassium sorbate is inhibitory towards Alteromonas putrefaciens (an organism active in the spoilage of proteinaceous foods) at near neutral pH. Electron microscopy and cell lysis studies suggested that the site of action is the outer membrane of the cell.

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Copyright the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). 1988. Thesis (Ph.D.)--University of Tasmania, 1988. Includes bibliographies. Spine title: Shelf-life and safety of packaged seafoods

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