Date of Award:

8-2021

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Nutrition, Dietetics, and Food Sciences

Committee Chair(s)

Luis J. Bastarrachea

Committee

Luis J. Bastarrachea

Committee

Marie K. Walsh

Committee

David Britt

Abstract

Food spoilage and contamination remains a common problem within the food industry. Furthermore, the continued change of consumer demand and perspective on food quality and products has led the food industry and researchers to find new methods of food preservation. Many of these new methods hope to use non-thermal processes since thermal processes tend to decrease the overall quality of the final product. Some new non-thermal methods that have been looked at are the use of high intensity ultrasound (HIU), ultraviolet light, and the use of natural antimicrobials. In this study, UHT milk inoculated with either E. coli K12 or L. innocua L2 was treated with a combination of HIU (30 s), UV-A light (15 min), and the addition of a natural, FDA approved, antimicrobial compound: Nisin or ε-poly(lysine). The treatments displayed the ability to inactivate the microorganisms by up to ~ 99.99% while using ~ 38 % less energy than traditional, thermal pasteurization. Samples were also stored for a period of 24 h at 4 °C (refrigeration temperature) or 25 °C (room temperature) following the treatment. The samples stored at 4 °C showed a slight, continued decrease in the number of microorganisms, or microbial load, while the majority of the samples stored at 25 °C had an increase in the overall microbial load. Thus, the optimal temperature for storage was found to be 4 °C. Minor changes in pH were observed as well as changes in the color, which were, however, not discernable with the visible eye.

This study also measured the ability of UV-A light to inactivate the same microorganisms on the surface of processed cheese. To decrease the microbial load by ~ 99.9999% a total of ~ 70 min of UV-A light was needed for E. coli K12 and ~ 130 min for L. innocua L2. The surface of the cheese was analyzed using infrared spectroscopy and showed no changes in the surface chemistry but did show a decrease in moisture content. Minor changes in the color of the surface were also observed which were hard to discern with the visible eye.

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