Combining lasers with emerging technologies for minimal processing

Tan, Boon Kiat (2003) Combining lasers with emerging technologies for minimal processing. PhD thesis, University of Glasgow.

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Abstract

Conservative estimates place the economic cost of food poisoning at hundreds of millions of pounds per annum. Recent market expansion of minimally processed fresh fruit and vegetables has resulted from the consumer's desire of convenience foods that have been peeled, cut, shredded or even washed. These produce, however, are likely to be contaminated. Such produce has a natural high microbiological burden. Minimally processing the food results in surface damage that is likely to favour bacterial adhesion. The cutting process leads to cellular damage, which coupled with increased adhesion and leakage of intracellular material, can lead to increased growth rate of spoilage organisms or pathogens. Minimally processed fruit and vegetables are often washed in water or water containing chemicals. The wash water can help distribute bacteria into the damaged sites on the processed fruit or vegetables. The use of chlorine has been associated with the production of carcinogenic and mutagenic substances and consequently there are fears over its use and potential accumulation within the body. Many government policies are encouraging people to eat more fresh fruit and vegetables. It is important therefore, that processors use the best practice available to supply fruit and vegetables with the minimum risk to consumers through digestion of pathogens and with a long a shelf life as possible to aid distribution channels, minimise waste and increase profits for processors. This research was seeking to identify novel ways to reduce the levels of contamination on carrots and potatoes and extend their shelf-life. Technology was developed to exploit different parts of the electromagnetic spectrum to kill bacteria. The systems included a CO2 laser, conventional UV lamps, and microwave irradiation. As an adjunct to these processes, H2O2 treatments and combination treatments were used. These systems were combined to kill bacteria on different substrates, fruit and vegetables. Comparison of shelf life tests and optimum treatment processes were also done. On carrots and potatoes the investigation of vitamin A and C levels, respectively, also indicated that their nutritious quality had not been degraded with any of the treatments. Using ozone as a bactericide and bioluminescence as a measurement of viability or metabolic activity, a real time monitoring system was developed to measure surface decontamination. The Escherichia coli strain DH5alpha PT7-3 with its plasmid encoded with ampicillin resistance contained the lux ABCDE genes from Xenorhadus luminescence, were used as the reference organism. Results showed that the bioluminescence responded instantaneously to treatment. Bioluminescence measurements were recorded in decibel, after 15 min of ozone treatment the bioluminescence was reduced by 4 dB and E. coli (lux) were inactivated. To investigate the response of various Gram-positive and Gram-negative organisms to ozone treatment, Campylobacter jejuni, Bacillus cereus, Escherichia coli, Listeria monocytogenes, Salmonella typhimurium and Staphylococcus aureus were inoculated on plates and treated with ozone. The treatment achieved about 2 - 2.5 D-value reduction on plates. The same treatment was less effective when the experiments were repeated on contaminated chicken and salmon samples. A log reduction range between 0.37 - 1.5 was achieved.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Advisers: Ian Watson; Roger Parton
Keywords: Food science
Date of Award: 2003
Depositing User: Enlighten Team
Unique ID: glathesis:2003-71218
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 10 May 2019 10:49
Last Modified: 10 May 2019 10:49
URI: http://theses.gla.ac.uk/id/eprint/71218

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