Evaluation of the antioxidant potential of selected lactic acid bacteria strains (Bachelor thesis)

Λιώκη, Άννα - Αφροδίτη/ Lioki, Anna - Afroditi

Lactic acid bacteria (LAB) are a diverse group of microorganisms that ferment carbohydrate to produce lactic acid. They can be found in various fermented products with some of them being known for their probiotic properties and health benefits. Hence, implementation of LAB strains in food technology, medicine and functional nutrition has become progressively popular. They have been characterised as GRAS (Generally Recognised as Safe) and among their probiotic attributes, some LAB strains also exhibit the ability to mitigate oxidative stress. Oxidative stress occurs when there is accumulation of reactive oxygen species (ROS) and the antioxidant mechanisms of the cell are unable to detoxify them. It can cause damage to nucleic acid molecules, lipids and proteins and provoke cancer, inflammation, ageing and gut diseases. Therefore, antioxidant molecules play a key role to the overall health and homeostasis of the organism. The aim of this study was the evaluation of the antioxidant potential of eleven LAB strains. Nine are wild type strains, isolated from various fermented products, such as dairy products, kefir, sausages, olives etc, and two are commercially available probiotic strains, Lacticaseibacillus rhamnosus GG and Lacticaseibacillus paracasei Shirota. For this reason, a set of experiments were performed. Firstly, the potential of the strains to survive in presence of oxidants was tested. The LAB strains were exposed to different concentrations of four different oxidative agents; hydrogen peroxide, tert-butyl hydroperoxide, ethanol and acetaldehyde and their survival ability was calculated by measuring the optical density of the culture medium at various time points. The three best performing strains along with the two probiotic strains, were selected. Following the initial screening, these five strains’ ability to survive in presence of oxidative agents was further studied, using the colony forming units assay, after exposure to the oxidative agents. The number of colonies formed was counted and used to determine the strains’ survival ability. Finally, investigation of the antioxidant potential of the five selected strains was conducted using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging assay. Three samples were collected form each culture, one containing the extracellular medium of the culture, one containing only the live cells and the third one contained the lysate of the bacterial cells produced after sonication. These samples were tested for the presence of components with potentially antioxidant activity by exposure to DPPH solution (0.1mM) for 30 minutes. Then, optical density measurement was performed to calculate each samples radical scavenging activity. Future studies will focus on the molecular and cellular mechanisms of antioxidant activity of selected LAB strains in skin, pancreas and intestinal experimental models.
Institution and School/Department of submitter: Δημοκρίτειο Πανεπιστήμιο Θράκης. Σχολή Επιστημών Υγείας. Τμήμα Μοριακής Βιολογίας και Γενετικής
Subject classification: Lactic acid bacteria
Keywords: Probiotics,Reactive oxygen species,Antioxidants,Προβιοτικά,Αντιοξειδωτικά,Δραστικές μορφές οξυγόνου
URI: https://repo.lib.duth.gr/jspui/handle/123456789/19647
http://dx.doi.org/10.26257/heal.duth.18338
Appears in Collections:ΤΜΗΜΑ ΜΟΡΙΑΚΗΣ ΒΙΟΛΟΓΙΑΣ & ΓΕΝΕΤΙΚΗΣ

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https://repo.lib.duth.gr/jspui/handle/123456789/19647
http://dx.doi.org/10.26257/heal.duth.18338
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