Document Type

Theses, Masters


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Publication Details

Successfully submitted for the award of Master of Philosophy (M.Phil) to the Dublin Institute of Technology, 2005.


Chlorine has widespread use commercially as a disinfectant wash for raw vegetables. However, it is an extremely corrosive gas and it may have severe health and environmental implications. The aim of this thesis was to find safe, alternative decontamination treatments for ready-to-eat Iceberg lettuce. The efficacy of 1% acetic acid, 2% citric acid; calcium lactate concentrations of 0.5%, 1.5%, 2.5% and 3% at wash temperature of 4,25 and 50°C, ozone alone (1 mg 1-1) and in combination with calcium lactate (2.5%) were compared with chlorine as decontaminating treatments. Microbiological analyses were performed following decontamination treatments using the pour plate method to enumerate coliforms and the spiral plate method for enumeration of mesophile, pseudomonad, psychrophile, Lactic Acid Bacteria and yeast populations. The behaviour of a challenge population of Escherichia Coli ATCC 25922 on Iceberg lettuce was also investigated for effects of temperature and decontamination treatment. The results reveal that while anti-microbial dipping resulted in significant decontamination, the efficacy of alternatives to chlorine was variable. Initial investigations of alternative strategies for reduction of the general indigenous microflora using calcium lactate, ozone alone or in combination with calcium lactate, resulted in decontamination efficacies less than chlorine but comparable to or better than washing in water. In a comparison of chlorine with organic acids, acetic acid or citric acid were the most effective, but the use of acetic acid is not recommended due to its negative sensory impact. However, critic acid or calcium lactate treatments were found to be reasonably successful alternatives to chlorine for microbiological decontamination of lettuce. A lag phase of 5 days was obtained for E. coli ATCC 25922 on calcium lactate treated lettuce, indicating its potential as a good alternative decontamination treatment. Treatment with 3% calcium lactate at 50oC offered the best alternative to chlorine. It appears that the application of a treatment at 50oC.