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Abstract
Conventional antimicrobials have been used extensively for decades to control microbialcontaminations in food. However, the emergence of multidrug-resistant foodborne bacterial
pathogens including Salmonella and enterohemorrhagic Escherichia coli necessitates the
exploration of effective and natural antimicrobials. The biologically active compounds derived
from plants are considered ideal alternatives to synthetic antimicrobials. Pomegranate is a
nutrient-dense fruit, rich in bioactive phytochemicals. As a food-byproduct, the inedible
pomegranate peels have been proven to contain higher amounts of functional substances than the
edible arils. The antimicrobial function of pomegranate peels is mainly attributed to the
hydrolyzable tannins, especially punicalagin. The primary objective of this project is to examine
and compare the antimicrobial properties of various pomegranate peels extracted with water and
ethanol. The phenolic profile of pomegranate peel aqueous and ethanolic extracts was
determined using the Folin-Ciocalteu method and high-performance liquid chromatography. In
addition, the correlations between the inhibitory effect of different phenolic extracts and their
phenolic content were established. Extracts were further added to sprouted nut butter to evaluate
their feasibility of being used as natural preservatives. Results revealed inhibitory activities in
both aqueous and ethanolic extracts against Salmonella and E. coli in tryptic soy broth with two
different concentrations of phenolics with varying degrees of inactivation. Punicalagin with two
anomers was the most abundant active compound in all pomegranate peel extracts. The
ethanolic extract was effective in deactivating Salmonella in sprouted nut butter. Nevertheless,
the extract, in combination with the seasonings used, could not eliminate Salmonella from the
food matrices. These findings indicate the potential application of the novel natural
antimicrobials derived from pomegranate peels. However, the extraction process needs to be
further optimized and the safe limits of its consumption should be further explored and clarified.
INDEX WORDS: Foodborne pathogens, Natural antimicrobials, Pomegranate peel, Aqueous
extract, Ethanolic extract, Inhibitory activity, Salmonella, Escherichia coli