Date of Award

Spring 5-1-2020

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)


Food Science and Human Nutrition


Jennifer Perry

Second Committee Member

Beth Calder

Third Committee Member

Seanna Annis


Maple syrup is produced by the extensive thermal evaporation of maple sap traditionally collected from the Acer saccharum tree and other maple varietals. The resulting low water activity product (Aw < 0.85) is classified by the FDA as a low risk food commodity, due to the moisture limitations which inhibit the growth of pathogenic microorganisms. However, recent outbreaks associated with other designated low risk products, including peanut butter and wheat flour, now challenge the current understanding of factors required to induce human illness. Among the most notorious bacterial pathogens, as few as ten bacterial cells, have been cited to cause infection. In addition to bacteria-based risks, fungal contaminants have also been noted to jeopardize safety due to the potential for mycotoxin production, penetrating beyond the immediate product surface.

The extensive heating process required to produce syrup from sap is sufficient to eradicate the majority of present microflora. However, post-process contamination scenarios, which are augmented by producer behaviors, can introduce microorganisms into the finished product. Among these risk factors include direct product contamination due to insufficient heating temperatures, or contamination of bottles, as a result of improper container storage. Therefore, the objectives of this work are to (i) determine the thermal inactivation (D-value) of

predominant bacterial pathogens (STEC, Listeria monocytogenes, Salmonella) in maple syrup heated to 180°F, a common bottling temperature, (ii) assess the effectiveness of commonly used bottling temperatures (180°F and 190°F) in the inactivation of bacteria (previously described) and fungal spores (Aspergillus and Penicillium) desiccated on the interior of several types of retail containers, (iii) determine the efficacy of applying a boiling water pre-fill treatment in eradicating microbial hazards, and (iv) assess the survival or growth capabilities of both bacteria and fungi in maple sap and syrup held under normal storage conditions.

The data from this work showed that when the syrup is heated to 180°F for at least 23 seconds, this heating method is sufficient to achieve a 5-log reduction (pasteurization) in the three bacterial pathogens we identified. However, when contaminants were desiccated on the interior of bottles, even a fill temperature of 190°F, is ineffective in eradicating all contamination risks. Although a boiling water pre-fill treatment reduced the likelihood of microbial survival, it did not eradicate all populations we studied across every container type. However, due to reduced heat retention capacity and bottle shape, utilizing a fancy glass bottle results in the greatest likelihood of microbe survival. Therefore, the largest plastic bottle at the highest fill temperature possible, is recommended to reduce product contamination risks. If contamination does occur, bacterial pathogens are capable of survival for up to 30 days in ambient maple syrup and up to 60 days in refrigerated maple sap. Producers may consider retaining finished product prior to sale in order to reduce the potential for bacterial food safety risks. Fungal (Aspergillus and Penicillium) contaminated syrup demonstrated continuous growth in both products. Therefore, it is recommended that fungal-contaminated syrup must be discarded due to the potential risks of mycotoxin production that could pose harm to consumer health.

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