Document Type

Theses, Masters

Rights

This item is available under a Creative Commons License for non-commercial use only

Disciplines

Microbiology

Publication Details

Successfully submitted for the award of Master of Philosophy (M.Phil) to the Dublin Institute of Technology, 2000.

Abstract

Compositional, physiological and microbiological changes in selected minimally processed vegetables packaged under a modified atmosphere of 2% oxygen and 5% carbon dioxide were monitored over a ten day storage period at 40 C and 80 C. The analysis targeted specific changes in the nutritional, chemical and physiological make up of the vegetables as well as the changes in the microbial levels. In addition the changes in the gas atmospheres within the packs were monitored. It has been widely accepted that modified atmospheres used to package fresh produce can preserve the product quality and thus extend the shelf life of the produce. An in-depth analysis of the effects of modified atmosphere packaging (MAP) on Irish vegetables has not been previously reported. In this study non-organically grown Irish produce comprising of broccoli ‘shogun’ (Brassica Oleracea L. (Botrytris)), carrots ‘Nairobi’ (Daucus carota L.) and cauliflower ‘Poirrot’ (Brassica Oleracea L. (Botrytris)) was studied. The samples were packaged in one of three different oriented polypropylene (OPP) films (thickness 35µm) the difference between each film being its permeability to oxygen. Once packaged and hermetically sealed with the appropriate atmosphere the vegetables were stored in a commercial refrigerator at the aforementioned temperatures and analysed on day 0, 4, 7 and 10. The results indicate that the nutritional losses measured by the rate of loss of ascorbic acid was greater in the control samples which had been air packaged however the temperature gradient both in the air and MAP samples was seen to influence the loss of ascorbic acid considerably. The 4°C MAP vegetables resulted is the greatest retention of the vitamin. Similarly, chemical analysis of the 4° MAP vegetables revealed that the compositional change (i.e. sugars, organic acids, pH and volatiles) were not as pronounced as those changes noted in the 8°C MAP and air packaged vegetables and also the 4°C air packaged samples. The psychological changes in colour and gas atmosphere were found to mimic the results observed for the chemical and nutritional analyses whereby the 4° MAP vegetables retained a more favourable gas atmosphere and the changes to pigments over the 10 day storage period were not as prominent as those detected in the vegetables stored under the other storage conditions (i.e. 4°C and 8°C air and 8° C MAP). The microbial spoilage of the vegetables packaged at 4°C MAP was delayed in comparison to the vegetables packaged under the aforementioned conditions. Overall the total microbial mesophilic counts for all the storage conditions were still considerably high (104 – 109 cfu/g.), while this in itself does not indicate produce spoilage the probability of pathogenic organism being present cannot be overlooked. In conjunction with the collated data presented with this thesis it is possible to recommend an extension of two days on the current industrial shelf life of five days for vegetables packaged and stored under similar conditions.

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