Laser sterilisation of bacterial and fungal spores

Armstrong, Graham N (2000) Laser sterilisation of bacterial and fungal spores. PhD thesis, University of Glasgow.

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Abstract

This work investigated the sterilisation efficiency of the Nd:YAG and CO2 laser. This work centred on micro-organisms that were important to the food industry and resistant to sterilisation. The efficiency of laser sterilisation was ascertained and quantified. The efficiency of incorporating laser, UV irradiation and heating of bactericidal chemicals was also investigated. These results will aid the future development of novel sterilisation systems. The Nd;YAG laser was found capable of sterilising stainless steel. The addition of UV gave an added effect. Nd:YAG laser heating of hydrogen peroxide gave a marked improvement in the chemical's killing efficiency. Nd:YAG irradiation completely sterilised B. cereus spores on discs of stainless steel (mass 5g) with an energy density of 1800Jcm2. By decreasing the beam diameter, the percentage of the beam in contact with the spores increased from 43% to 72% but killing remained the same. Calorimetry showed that after exposing steel discs to 1800Jcm2 with a beam diameter of 16 and 8mm the temperature of the steel was the same. Possible killing mechanisms were looked into and it was found that for the Nd:YAG laser it was primarily thermal, and not due to direct photonic interaction. This hypothesis was supported by the killing of spores on 2mm thin steel discs (mass 0.8g) with an energy density 120Jcm2. This was due to the thin steel heating up rapidly with the relatively low energy density. Electron microscopy showed that the spores responded cytologically in the same way after heating by Nd:YAG laser irradiation and water-bath heating. It was attempted to increase the laser's killing effect by combining the laser with UV irradiation from 2, 8W UV lamps (254nm wavelength). Lawns of B. cereus spores were made and exposed to Nd:YAG laser irradiation (ED 3000Jcm2). No clearing was observed. By adding UV irradiation (sequentially) the diameter of clearance caused by the laser irradiation increased. To quantify the killing, aliquots of spore suspensions were raised in temperature with Nd:YAG laser irradiation to 90

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Ian Watson
Keywords: Electrical engineering, Agricultural engineering, Food science
Date of Award: 2000
Depositing User: Enlighten Team
Unique ID: glathesis:2000-71983
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 17 May 2019 13:32
Last Modified: 17 May 2019 13:32
URI: http://theses.gla.ac.uk/id/eprint/71983

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