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Novel Antimicrobial Activity of Lactic Acid Bacteria Isolated from Taro Peels

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Item Summary

Title: Novel Antimicrobial Activity of Lactic Acid Bacteria Isolated from Taro Peels
Authors: Li, QianTing
Issue Date: Dec 2015
Publisher: [Honolulu] : [University of Hawaii at Manoa], [December 2015]
Abstract: Pathogenic bacteria have caused a large number of foodborne illnesses and great economic loss in food and animal production. Salmonella and Listeria are two notorious foodborne pathogens with high prevalence and severity. It is urgently needed to find effective measures to control these pathogens. Taro is the staple of native Hawaiian diet and an important part of Polynesian culture. Taro peels, a by-product of poi, are removed from taro after pressure cooking. Pigs were found to recover from gastrointestinal illness when fed pressure-cooked taro peels. It was hypothesized that lactic acid bacteria (LAB) survived the high-pressure condition may be present in taro peels and responsible for the recovery.
The first objective of this study was to identify dominant bacterial species present in taro peels and determine their antimicrobial potential against pathogenic bacteria. Samples from four poi manufacturers on Oahu and Maui were collected and analyzed. After 48 h of natural fermentation, LAB isolates were obtained on selective MRS agar and identified by RAPD-PCR and 16S rDNA gene sequencing. Representative LAB strains were tested for their acid and bile tolerance. Culture supernatants of LAB isolates with strong acid and bile tolerance were evaluated on their bactericidal properties against Salmonella Typhimurium and Listeria monocytogenes. A total of 159 isolates belonging to 11 different LAB species were obtained, of which majority were Leuconostoc spp. L. mesenteroides strains accounted for approximately 40% of all isolates; L. lactis, L. pseudomesenteroides, Lactococcus lactis, and Weissella confusa also frequently occurred in the sample. Four isolates #67, #97, #101 and #137 exhibited high tolerance to low pH and bile, thereby enabling them to survive in the gastrointestinal environment. The LAB isolates showed different antimicrobial effects on the tested pathogens. S. Typhimurium and L. monocytogenes died in the culture supernatants within 2 h and 8 h, respectively.
Moreover, this study also aimed at exploring the production of bacteriocins by the LAB isolates. Agar well diffusion assay was performed to determine the sensitivity of antimicrobials in the culture supernatants to proteinase K. Additionally, the inhibitory effect of neutralized supernatants on the indicator bacteria was evaluated by spot-on-lawn and broth enumeration assays. Proteinase K treatment reduced the inhibition zone of certain supernatants against L. monocytogenes. Neutralization eliminated the antimicrobial effect of organic acids toward the tested pathogens. Only the supernatant of one isolate #137 Lactococcus lactis still retained the bactericidal activity against L. Monocytogenes. PCR-based methods were used to detect the bacterocin-encoding genes in the LAB isolates. No gene related to class IIa bacteriocins has been amplified, while two bacteriocin structural genes were amplified by primers NisZ and Bac147 using genomic DNA of isolate #137 as template. This is the first Lactococcus lactis strain reported to carry these two bacteriocin genes simultaneously. The anti-Listeria bacteriocins produced by the Lactoccus lactis strain were heat-stable but sensitive to proteinase K and pronase E. Isolate #137 is potentially a novel bacteriocin-producing Lactococcus lactis strain.
Both organic acids and bacteriocins may account for the antimicrobial activity of LAB isolated from taro skins. These isolates could potentially be used as probiotics to fight bacterial infections and confer other health benefits in humans and animals. With the ability to survive pressure-cooking, these isolates have potential to be used in food production. Bacteriocins produced by the isolates would offer a very promising biocontrol tool for inhibiting pathogenic bacteria in food.
Description: M.S. University of Hawaii at Manoa 2015.
Includes bibliographical references.
URI/DOI: http://hdl.handle.net/10125/51171
Appears in Collections:M.S. - Food Science


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