Antimicrobial Activities of Brewed Roasted Coffee of Different Species (Coffea arabica, Coffea robusta and Coffea liberica)

Tan, Hui San (2020) Antimicrobial Activities of Brewed Roasted Coffee of Different Species (Coffea arabica, Coffea robusta and Coffea liberica). Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

Coffee is one of the most popular brewed beverage that is widely produced and consumed since 16th century. In the past decade, several researches including antimicrobial test had been conducted on Coffea arabica and Coffea robusta to access their potential health benefits. However, there was limited study on antimicrobial properties on our locally homegrown coffee species, Coffea liberica. In this study, three brewed roasted coffee species, which were C. arabica, C. robusta and C. liberica were chosen for the study against Proteus mirabilis, Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae. The aim of this study was to access the antimicrobial profile of the three coffee beans and their mechanism of action. The extracts were tested by Kirby-Bauer disk diffusion assay and broth microdilution assay to investigate the minimum inhibitory concentration (MIC). The results revealed that C. arabica and C. robusta had shown significantly higher antimicrobial activity than C. liberica towards P. mirabilis, P. aeruginosa and K. pneumoniae. Among the tested bacteria, K. pneumoniae was shown to be significantly more susceptible than other organisms towards the coffee extracts. The MIC values against K. pneumoniae was 2000 ug/mL, 4000 ug/mL and >4000 ug/mL for C. robusta and C. arabica and C. liberica respectively. Phytochemical analysis in our previous research had shown that chlorogenic acid content was significantly the highest in C. liberica (0.905±0.0761mg/100g) and caffeine content was significantly the highest in C. robusta (2.630±0.1243mg/100g). However, caffeic acid was not detected. It was postulated that the virulence factors present in K. pneumoniae could be inhibited by caffeine found in coffee extracts leading to bacterial growth inhibition. Through literature search, four of the K. pneumoniae virulence proteins (IucA, IucC, MrkD and TonB) were available as crystalized structures in Protein Data Bank. Hence, molecular docking work is currently on-going to determine binding efficacy of caffeine against the aforementioned proteins. KEYWORDS: coffee, antimicrobial, disc diffusion, broth microdilution, virulent factors, C. arabica, C. robusta, C. liberica