Date of Award

Spring 5-8-2020

Level of Access

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Food Science and Human Nutrition

Advisor

Jennifer Perry

Second Committee Member

Beth Calder

Third Committee Member

Balunkeswar Nayak

Additional Committee Members

Robson A. M. Machado

Gregory Porter

Abstract

The Dietary Guidelines for Americans recommend dairy products as part of a healthy diet and these products are significant contributors of important nutrients. In the U.S., and Maine specifically, demand for locally-produced, minimally processed foods, including unpasteurized dairy, has increased during the past several decades. An analysis of retrospective microbial testing data for unpasteurized retail dairy products revealed increasing microbial quality from 1998-2016, despite a five-fold increase in sample numbers during this time. Higher percentages of samples were non-compliant with microbial quality standards during the summer months compared to winter. High coliform counts were the leading cause of non-compliant samples in milks and other dairy-based products. The second objective of this research was to investigate the effects of cheesemaking and aging temperature on levels of inoculated foodborne pathogens. The cheesemaking process did not affect the populations of either pathogen of interest. During aging, lower temperatures (4℃ and 10℃) significantly decreased population of Shiga-toxigenic E. coli, whereas only 4℃ significantly reduced L. monocytogenes. Aging at 4℃ was also effective in maintaining the population of the starter culture. The highest aging temperature (22℃) caused a significant increase of both pathogens as well as a significant increase in pH levels and softening of the cheese texture. In tests of unpasteurized retail dairy products, the highest rates of presumptive positive results for Listeria spp. were recorded in July and August. The prevalence of presumptive positive Listeria spp. was higher in mold-ripened compared to soft cheeses. There was a significant positive correlation between non-compliant levels of coliforms and presence of presumptive positive Listeria spp. in the samples tested. The results of this research suggest that the overall quality of the expanding unpasteurized dairy sector in Maine has remained constant or improved in the past two decades. Small-scale cheese operations participating in this market should use refrigeration temperatures for aging of cheese when possible, which will provide the best control against foodborne pathogens. Finally, more targeted testing techniques are suggested to detect the potential sources of coliforms and to ensure the safety of unpasteurized dairy commodities.

Share