Abdullahi Adam | ALES Graduate Seminar

Date(s) - 15/01/2021
1:00 pm - 2:00 pm

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 Abdullahi Adam. This seminar is open to the general public to attend.

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Thesis Topic: Microbial Decontamination and Rapid Cooling of Fresh Food Products by Plasma Integrated Low-Pressure Cooling

MSc with Dr. Roopesh Syamaladevi.

Seminar Abstract:

Fresh food products, including fruits, vegetables, raw meat and poultry have been associated with safety concerns and quality issues, owing to their susceptibility to rapid deterioration and microbial contamination. This research aimed to develop an integrated process to simultaneously cool and decontaminate high moisture food products.

Cold plasma (CP), a novel decontamination technology, was integrated with vacuum cooling to develop a plasma integrated low-pressure cooling (PiLPC) process. To evaluate the rapid cooling and microbial inactivation efficacies of the PiLPC process, fresh cut Granny Smith apples and Salmonella enterica serovar Typhimurium ATCC 13311 were used as the model food and microorganism, respectively. The influence of process parameters including treatment time, pressure, and post-treatment storage on inactivation of Salmonella on fresh-cut apples was investigated. Inactivation of Salmonella increased with treatment time, with a maximum reduction of 3.21 log CFU/g after 5 min of CP treatment at atmospheric pressure. Inactivation Salmonella after CP treatment at 200 mbar were not significantly different from those at atmospheric pressure for the same treatment time. However, there was a significant decrease in the inactivation of Salmonella when samples were treated with CP at 50 mbar as compared to atmospheric pressure. Post-treatment storage at ~4 oC for 3 days after 3 min of CP treatment at 200 mbar reduced the total Salmonella population by > 6 log CFU/g. Depending on the sample surface to volume ratio, the cut apple temperature was reduced from room temperature to 1 °C in 3 to 7 min, when the pressure was reduced to 7 mbar. However, this PiLPC process resulted in moisture loss in cut apples.

The second part of this research aimed to achieve higher rates of inactivation of Salmonella without an increase in CP treatment time, to reduce the moisture loss in fresh foods during the PiLPC process, and to improve the quality-related issues such as cut-edge enzymatic browning. This study evaluated and compared the effects of citric acid (CA) and CP alone and in combination on the inactivation of Salmonella, polyphenol oxidase (PPO) activity and the resulting enzymatic browning, the total phenolic content, and the moisture loss of cut-apples. The highest inactivation of Salmonella (5.68 log CFU/g) was observed after treatment of cut apples dipped in 5 % CA for 2 min combined with 3 min CP treatment. The highest PPO inactivation was observed when cut apples were dipped in 5 % CA for 2 min and then treated with 3 min of CP. The color of cut apples remained relatively unchanged with fresh like appearance during 7 days of storage after this combined treatment. Although the cooling time was increased when samples were pre-dipped in CA, it reduced the moisture loss of cut apples by more than 50 % during the PiLPC process. No significant reduction in phenolic content was observed during the PiLPC when the samples were pre-dipped in 5 % CA. These results indicate the potential of the PiLPC process for rapid cooling, microbial, and enzymatic inactivation in fresh food products. Future research using different fresh food products and other important pathogens is required to further develop this technology for industrial applications.