Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Food Science and Human Nutrition


Food Science and Technology

First Advisor

Kevin M. Keener


Driven by the industrial needs and interests to ensure the safety of soft cheeses, such as queso fresco, my studies have focused on assessing the capability of high voltage atmospheric cold plasma (HVACP), a novel non-thermal technology, in microbial inactivation for its potential application in soft cheese production to remove pathogens from post-processing contaminated cheeses. A variety of treatment conditions were evaluated including three gas blends (air; MA65: 65% O2, 30% CO2, 5% N2; MA50: 50% CO2, 50% N2), three voltages (60 kV, 80 kV, and 100 kV) and two modes of exposure (direct vs. indirect). Direct mode of exposure was found to be more efficient in inactivation of Listeria innocua, non-pathogenic surrogates for Listeria monocytogenes, and matrix with more complex surface structure and higher nutrients was more resistant to microbial inactivation by HVACP treatment. Increased voltage showed higher efficiency for microbial inactivation in queso fresco and HVACP treatment was found to be more effective in inactivation of the gram-negative bacteria (E.coli K-12) compared to the gram-positive (Listeria innocua). Minimal changes in pH, moisture and color were observed with no significant changes (p<0.05) in the texture of queso fresco after HVACP treatment. Moreover, dry air direct HVACP treatment for queso fresco was shown to be more efficient in Listeria innocua inactivation compared to MA50 treatment as reactive oxygen species play an important role in microbial inactivation. Lastly, the direct HVACP in dry air demonstrated its ability in inhibiting the growth of Listeria innocua and background microflora in queso fresco with extended refrigerated storage. This research has demonstrated the effectiveness of HVACP for decontamination of soft cheeses ensuring the safety as well as extending the shelf-life of the cheese.

Copyright Owner

Zifan Wan



File Format


File Size

189 pages

Available for download on Thursday, April 22, 2021

Included in

Food Science Commons