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Improving the safety of dairy products by evaluation of lactose oxidase as an enzymatic control method for Listeria monocytogenes growth and qualitative analysis of artisan dairy food safety workshops

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Abstract

Listeria monocytogenes is a pathogen of concern in the dairy industry due to its ubiquitous nature and ability to thrive and proliferate at refrigeration temperatures. Certain dairy products are ready-to-eat (RTE) and provide an environment for L. monocytogenes to thrive. Consumption of the pathogen by consumers can cause morbidity and mortality in immunocompromised individuals and the fetuses of pregnant women. Consumers are currently moving toward a trend of desiring clean- label products, so a clean-label antimicrobial that is effective at controlling L. monocytogenes growth in dairy products would be beneficial to the dairy industry. Lactose oxidase (LO) would fall into this clean label category because it is produced by a strain of mold. LO oxidizes lactose into lactobionic acid (LBA) with the concurrent reduction of oxygen into hydrogen peroxide (H2O2). H2O2 has long been used in the dairy industry as an antimicrobial and has shown promising results on inhibition of L. monocytogenes in dairy products in previous studies. Incorporation of LO into dairy products may provide an effective control method for L. monocytogenes growth. H2O2 could also activate the lactoperoxidase system (LPS), an antimicrobial system that is present in raw milk to provide further control of the pathogen. We first evaluated the effect of different concentrations of LO on L. monocytogenes growth in UHT skim milk in both the long-term and the short-term and then evaluated different concentrations of LO combined with sodium thiocyanate (TCN), a component of the LPS, in fluid raw milk. We found that LO and LO-TCN combinations yielded promising results on inhibition of L. monocytogenes in fluid milk, and then moved to evaluate the effect of LO and LO-TCN combinations against L. monocytogenes in a laboratory-scale fresh cheese model. Various contamination scenarios and applications of LO and LO-TCN combinations were tested in this fresh cheese model to observe the antimicrobial effect of the combinations at various points in the production process. LO alone was discovered to inhibit L. monocytogenes at a concentration of 0.12 and 0.6 g/L at low inoculum levels on the surface of the cheese and at both higher and lower inoculum levels when the enzyme was added into fluid milk, indicating that the production of H2O2 was sufficient to reduce pathogenic growth. We also analyzed qualitative data from artisan dairy food safety workshops to determine the effect of formal education on artisan dairy producers in terms of their food safety knowledge, attitudes to food safety practices, and levels of food safety implementation in their facilities. It was found that these workshop enhanced participants’ knowledge of food safety, and post-workshop, they had a more optimistic perspective of various components of their food safety plans. These results will be used to determine if formal education changed the food safety knowledge, attitudes to food safety practices, and levels of food safety implementation of artisan producers, post-workshop. In the future, these results will be used to evaluate and improve artisan dairy food safety workshop courses that Cornell holds throughout various geographic locations in the United States.

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153 pages

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2021-08

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Enzymes; Lactose oxidase; Listeria; Milk; Queso fresco

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Committee Chair

Alcaine, Samuel David

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Worobo, Randy W.

Degree Discipline

Food Science and Technology

Degree Name

M.S., Food Science and Technology

Degree Level

Master of Science

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Government Document

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dissertation or thesis

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