Vliv extraktů kůry vybraných kambodžských rostlin na etanolové kvašení a růst kontaminujících mikroorganismů v nápojích

Bc. Polina Cherepanova

Diplomová práce

Abstract:

Natural palm sap has been known as a tasty and refreshing beverage in tropical countries. In Cambodia, it is traditionally preserved with the addition of plant barks with probable but unproven antimicrobial activity. Ten ethanolic and aqueous extracts from five Cambodian plant barks were tested in vitro by the broth microdilution method. The results were determined as minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC). Extracts of Azadirachta indica A. Juss., Careya arborea Roxb., Hopea odorata Roxb., Hopea pierrei Hance, and Shorea roxburghii G. Don were tested against pathogenic (Escherichia coli, Staphylococcus aureus, Bacillus cereus, Pseudomonas aeruginosa, Candida albicans) and ethanol producing microorganisms (Hanseniaspora jakobsenii, Hanseniaspora uvarum, Leuconostoc palmae, Metschnikowia pulcherrima, Pantoea agglomerans, Saccharomyces cerevisiae, Zymobacter palmae and Zymomonas mobilis subsp. pomaceae). In addition to selected standard strains from ATCC and DSM collections, several wild yeasts and bacterial strains were isolated from fruits and determined with MALDI-TOF MS. All plant extracts demonstrated certain degree of antimicrobial activity against some of the tested microorganisms (MIC range 64–1024 μg/ml). As the most active plant extract due to a broad range of inhibited microbes and lowest MIC values (64 µg/ml against S. aureus and S. cerevisiae DSM 70478) was the ethanolic extract of H. odorata, followed by A. indica and C. arborea. All three ethanolic extracts also showed bactericidal effects against most of the tested Gram-positive bacteria, C. arborea and A. indica even demonstrated bactericidal effect against Gram-negative E. coli (1024 μg/ml). On the other hand, the least efficient extracts were the aqueous ones obtained from H. pierrei and S. roxburghii. A. indica and C. arborea ethanolic extracts affected the growth of yeast cells in a concentration-dependent manner, namely C. albicans, H. uvarum, and S. cerevisiae. Low concentrations of extracts (8-16 µg/ml) prevented cell death and increased their growth, while medium concentrations (32-128 µg/ml) were able to fully inhibit the growth of yeasts, and higher concentrations (256-1024 µg/ml) were predominantly not efficient for growth-inhibition. This hormetic effect of these extracts has not been previously described in the scientific literature and could be investigated more explicitly. The trial fermentation test has been performed and three yeasts, namely H. uvarum T5, M. pulcherrima T9, S. cerevisiae DSM 70465 were chosen for the further experiments with Cambodian plant extracts. The yeasts were selected due to their good fermentative ability indicated by the highest values of produced ethanol detected by GC-FID. The results of this thesis suggest all tested extracts as perspective material for further isolation and identification of active antimicrobial compounds that can be used as potential beverage preservatives.

Keywords

Careya arborea, Hopea odorata, Hopea pierrei, Shorea roxburghii, fermentation, Azadirachta indica

Jazyk práce: angličtina

Datum vytvoření / odevzdání či podání práce: 3. 5. 2021

Obhajoba závěrečné práce

• Vedoucí: Ing. Pavel Nový, Ph.D.
• Oponent: Marie Netopilová, Ing.

Česká zemědělská univerzita v Praze

Fakulta agrobiologie, potravinových a přírodních zdrojů

Magisterský studijní program:
Výživa a potraviny