2:00 pm - 3:00 pm
Event details: A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES PhD Final Exam Seminar by Amritha Prasad. This seminar is open to the general public to attend.
Thesis Topic:
Antimicrobial applications of treatments using light pulses emitted from light emitting diodes (LED)
Public Seminar:
https://ualberta-ca.zoom.us/j/94260507064?pwd=dnE1RGtaOW5IcG5ZQjR5QUgrUjBYZz09
Meeting ID: 942 6050 7064
Passcode: 934110
PhD with Dr. Roopesh Syamaladevi
Seminar Abstract:
Low water activity (aw) foods have been associated with several foodborne outbreaks and recalls. Eradication of foodborne microorganisms like Salmonella and Escherichia coli from low aw foods is challenging, as they are resistant to conventional decontamination practices. High intensity light pulses emitted from the Light Emitting Diode (LED) is an emerging decontamination technology, which is based on photodynamic inactivation. The overall objective of this research was to evaluate the inactivation efficacy of light pulses with selected wavelengths emitted from LEDs against foodborne pathogens at low and high aw conditions and their biofilms and to understand their antimicrobial mechanisms.
First, the effects of the selected process and product parameters on the inactivation efficacy of LEDs emitting light pulses of 365 and 395 nm wavelengths against S. Typhimurium and E. coli in low aw conditions were studied. The 365 nm LED treatments were more effective at low and high aw conditions than the 395 nm LED treatments with the same dose. The second study focussed on evaluating the antibacterial efficacy of 455 nm LED treatment against Salmonella in dry powdered form and in low aw pet foods. S. Typhimurium in dry powdered form was more resistant to the 455 nm LED treatment than in 0.75 aw pet foods. Pre-treatment of Salmonella inoculated 0.75 aw pet foods with 275 nm LED improved the inactivation efficacy of 455 nm LED treatment. Significant weight loss, surface temperature increase, and aw reduction were observed in LED treated samples, indicating the drying potential of the 365, 395 and 455 nm LED light pulses. Also, significant effects of treatment time (or dose), strains used, sample type, power level, and illumination conditions were observed on the inactivation efficacy of the LED treatments.
The third study focussed on understanding the antibacterial mechanisms of the 365, 395 and 455 nm LED treatments against S. Typhimurium at low aw conditions. A significant increase in the intracellular reactive oxygen species production and membrane lipid oxidation, after 365, 395 and 455 nm LED treatments were observed. The 395 nm LED treatments produced more membrane lipid oxidation in S. Typhimurium cells than the 365 nm LED treatment with the same dose.
Foodborne microorganisms can form biofilms on surfaces. Therefore, the fourth study focussed on understanding the efficacy of 275 and 455 nm LED treatment against single and mixed species biofilms of S. Typhimurium and Aeromonas australiensis on stainless steel surface. Both the LED treatments showed promising inactivation efficacy against S. Typhimurium and A. australiensis in single and mixed species biofilms. The sensitivity of A. australiensis towards 455 nm LED treatment was influenced by the presence of S. Typhimurium in the mixed species biofilms. Significant cell membrane damage of mixed species biofilms was observed due to the LED treatments.
This research shows the drying potential and the inactivation efficacy of the LED technology against foodborne pathogens in low aw conditions and their biofilms. The knowledge gained in this research would help in further research and in the development of LED technology as an alternate decontamination technology.
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