Samir Subedi | ALES Graduate Seminar

A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc Final Exam Seminar by Samir Subedi. This seminar is open to the general public to attend.
Thesis Topic: High Intensity Pulsed Light Emitting Diode (LED) Treatment for Simultaneous Salmonella Inactivation and Drying of Food Products

MSc with Dr. Roopesh Syamaladevi

Seminar Abstract:

According to world health orgnization, almost 600 million people, or 1 in 10 people suffer from food borne illnesses globally. Food industry uses several intervention methods to produce safe food products however, cases of food recalls and outbreaks due to microbial pathogens keep increasing every year. High intensity light pulses, emitted from Light Emitting Diode (LED) have the potential to reduce microbial pathogens in food products. Additionally, the light pulses from LEDs have the ability to dry food products. The overall research objective of this thesis was to determine the efficacy of high intensity light pulses with specific wavelengths to inactivate Salmonella and dry food products simultaneously, inside a newly developed LED reactor. The first part of this research used light pulses with 275, 365, 395, and 455 nm wavelengths, emitted from LEDs to inactivate a 5 strain cocktail of Salmonella in wheat flour at 40%, 75% and 90% environmental relative humidity (RH) conditions. The 60 min treatment of the wheat flour using 275, 365, 395, and 455 nm light pulses at 25°C and 75% RH resulted in 1.07, 2.42, 3.67, and 2.64 log reductions in Salmonella, respectively. For a same energy dosage of 1199 J/cm², treatments using 365, 395, and 455 nm light pulses resulted in 2.22, 2.48, and 1.61 log reductions in Salmonella in wheat flour, respectively. Environmental RH did not have significant influence (p≥0.05) on Salmonella inactivation in wheat flour during LED treatments. Initial water activity of wheat flour had a significant influence (p<0.05) on the reductions in Salmonella during LED treatments. Significant temperature increase resulted in decrease in water activity and drying of wheat flour during LED treatments with 275, 365, 395, and 455 nm light pulses.

In the second part of this research, an LED reactor using 395 nm light pulses with a vibratory platform and mild hot air fluidzation was developed to achieve simultaneous decontamination and drying of food products. Pet food pellets were inoculated with two strain cocktail of Salmonella and treated in three modes i.e., (1) using LED treatment alone; (2) vibration + mild hot air (50 ^oC) fluidization, (3) inside LED reactor (LED treatment + vibrations + mild hot air (50 ^oC) fluidization). The highest average reduction of 2.26 log was observed after 30 min treatment of pet food pellets using the LED reactor. The water content of pet food pellets was decreased from 0.27 to 0.06 kg water/kg dry solids, while the water activity decreased from 0.9 to 0.44 after 30 min treatment using mode 3, showing the fast drying efficacy of the LED reactor. Page and Weibull models were fit to describe the pet food drying kinetics while log-linear and Weibull models were used to fit the Salmonella inactivation kinetics. Significant lipid oxidation in pet food pellets was observed during LED treatment. The results suggest that the LED treatment is a promising method for achieving simultaneous Salmonella inactivation and drying of food products. An LED based process can be developed in the future at the industrial level to achieve drying and decontamination of food products in a single processing step, with integration of approaches to reduce product oxidation.