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

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Statham, Jo (Jo Anne) (1987) Evaluation of factors affecting, and methods for extending, the shelf-life of packaged seafoods. PhD thesis, University of Tasmania.

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Abstract

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.

Item Type: Thesis (PhD)
Keywords: Fishery products, Fishery products
Copyright Holders: The Author
Copyright Information:

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.

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1988. Includes bibliographies. Spine title: Shelf-life and safety of packaged seafoods

Date Deposited: 03 Feb 2015 03:25
Last Modified: 11 Mar 2016 05:55
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