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Current PhD. Theses

Properties of non- starter lactic acid bacteria

Dissertation solver: Eva Musilová, MSc
Supervisor: Horáčková Šárka, Assoc.Prof. MSc , PhD ( sar...@vscht.cz)

Annotation: In the production and cheese ripening, a wide consortium of microorganisms is used, the most important of which are lactic acid bacteria (LAB). These are used both as starter and adjunct cultures and, on the other hand, they enter the process as so-called non-starter lactic acid bacteria (NSLAB), which mainly include facultatively heterofermentative lactobacilli and enterococci. The influence of these bacteria is strain specific and depended on technological process and interactions with other microorganisms present in cheese. From the NSLAB group, new strains with significant functional properties can be selected and their potential as adjunct cultures with a positive effect on the ripening of the given types of cheese can be used. On the other hand, they can cause defects in cheese (gas production, production of biogenic amines) or be a reservoir of transferable antibiotic (Atb) resistance genes. Monitoring the transmission of Atb resistance genes in the food chain is one of the current trends in food safety control. This issue is described in more detail in defined cultures of LAB or in probiotic strains, but little data is known about NSLAB resistance.
The aim of the PhD thesis will be the isolation and characterization of NSLAB strains from raw milk, cheeses made from raw and pasteurized milk in terms of functional (technologically important, protective and probiotic) characteristics, Atb resistance and other. The risk of NSLAB as a potential reservoir of Atb resistance genes will be assessed. Suitable strains of LAB with documented properties will be deposited in the Czech Collection of Dairy Microorganisms Laktoflora and their activity will be verified in experimental cheese productions.

Preparation and sustainable extraction of bioactive unsaturated fatty acids

Dissertation solver: Radek Beneš, MSc
Supervisor: Kyselka Jan, Assoc.Prof. MSc , PhD (jan.kyselka@vscht.cz)

Annotation: The long- and very long-chain unsaturated fatty acids of the ω-3 and ω-6 series are important precursors of oxylipins. These are diverse biologically active fatty acid derivatives with different hydrocarbon chain lengths and different numbers of double bonds in an all-cis arrangement. According to the number of carbon atoms in the oxylipin molecule, we distinguish octadecanoids (C18), eicosanoids (C20), docosanoids (C22) and the newly discovered lipid mediators derived from very long polyunsaturated fatty acids (VLC-PUFA), which are referred to as elovanoids (C26-C40). Oxylipins, which occur in free form and also as their conjugates, influence a number of vital processes such as platelet aggregation (thromboxanes), vasoconstriction and vasodilation (prostaglandins), pro-inflammatory effects (e.g. cysteinyl-LTE4), activation and infiltration of neutrophils at the site of inflammation (hepoxilins), resolution of inflammation (resolvins, maresins and protectins), protection of retinal pigment epithelial cells (elovanoids) and others. The aim of this work will be to optimize laboratory preparations of unusual unsaturated and alkyne-tagged fatty acids. Testing of biological activities will be carried out in collaboration with partner University of Oklahoma (USA). Furthermore, a sustainable way of extracting selected unsaturated fatty acids from non-traditional commodities such as krill oil will be discovered.

Fractionation of prebiotic galactooligosaccharides and their application properties

Dissertation solver: Dmytro Harkavchenko, MSc
Supervisor: Čurda Ladislav, Assoc.Prof. MSc , PhD ( cur...@vscht.cz)

Annotation: Galactooligosaccharides (GOS) prepared by trangalactosylation from lactose using β-galactosidase contain large amount of monosacharides and also unreacted lactose. Content of GOS is rarely higher than 50 % in commercial products. Product with high added value can be obtained by isolation of GOS, annual growth rate of GOS production is more than 10 %. Fractionation in preparative scale is necessary for study of GOS properties, e.g. using preparative chromatography. The aim of thesis will be selection of suitable layout of enzymic reaction, which ensures maximal yield of GOS and minimal content of residual lactose. Obtained GOS will be isolated and separated to fractions with different polymerization degree or with different structure. Prebiotic and other properties important for application in fermented products will be studied.

Characteristics and functional properties of sourdough with lactobacilli

Dissertation solver: Daniel Koval, MSc
Supervisor: Horáčková Šárka, Assoc.Prof. MSc , PhD ( sar...@vscht.cz)

Annotation: Sourdoughs are increasingly used in current processing of bakery products due to wide range of their positive functional properties. Sourdoughs are fermented mixtures of water and different types of flour. Their benefits are related to the metabolic activities of yeasts and especially different species of Lactobacillus genus, such as lactic fermentation, proteolysis and synthesis of flavor compounds together with the production of substances preventing subsequent microbial contamination of products.
The aim of the thesis will be preparation and comparison of the sourdoughs from various cereals and pseudocereals and their analytical and nutritional assessment. Attention will be paid to the presence of particular groups of microorganisms focusing on the genus Lactobacillus, the characterization of newly isolated strains with emphasis on their antibacterial and antifungal activities. Furthmore, the effect of present microflora on the quality of prepared sourdoughs, dough and bakery products, especially on the changes of polysaccharides and products aging with additions of various kinds of sourdoughs will also be evaluated.

Synthesis and analysis of very-long-chain polyunsaturated fatty acids and their use for the preparation of bioactive compounds

Dissertation solver: Tereza Honzíková, MSc
Supervisor: Kyselka Jan, Assoc.Prof. MSc , PhD ( KYS...@vscht.cz)

Annotation: Very long-chain polyunsaturated fatty acids (C≥26; VLC-PUFA) are one of the least studied groups of fatty acids in the human body. Their structure, the length of the hydrocarbon chain and the number of all-cis double bonds, defines their unique physicochemical properties. They occur naturally in the retina of the eye, where they play an indispensable role for the proper functioning of vision; in the testes and sperm, whereby they significantly affect fertility. In the brain, also in the retina, they serve as precursors for signalling molecules with neuroprotective function - the so-called elovanoids. The biosynthesis of VLC-PUFA is based on eicosapentaenoic, docosahexaenoic and arachidonic acids. Due to rare genetic disorders, the organism is not capable of endogenous biosynthesis. Their deficiency has a significant impact on the health and development of the organism, as well as on the quality of life. Dietary intake is a suitable way to compensate for the lack of VLC-PUFA derivatives, but foods of plant or animal origin do not contain VLC-PUFA. There is therefore no suitable source. The aim of this work is to prepare VLC-PUFA in cost-efficient and inexpensive synthetic pathway by using natural sources rich in precursors, for example, by applying fish oils and their concentrates. The next step will be to investigate the enzymatic interesterification of VLC-PUFA and triacylglycerols or glycerophospholipids. The dissertation process will involve active collaboration with the University of Oklahoma Health Sciences Center, Dean McGee Eye Institute.

The effect of the modification of milk protein by microbial transglutaminase on the functional properties of milk.

Dissertation solver: Štěpán Marhons, MSc
Supervisor: Štětina Jiří, Assoc.Prof. MSc , PhD ( ste...@vscht.cz)
Čurda Ladislav, Assoc.Prof. MSc , PhD ( cur...@vscht.cz)

Annotation: Treatment of milk by microbial transglutaminase (protein-glutamine gamma-glutamyltransferase,EC 2.3.2.13)produces both intra- and intramolecular isopeptide linkages of amino acid residues of glutamine and lysine in milk proteins. These results in their cross-linking and modification of the course of milk clotting and coagulate properties. The aim of the thesis will beto evaluate the influence of transglutaminase and its application on the texture and stability of fermented dairy products and selected types of cheese.

Study of the influence of antimicrobial substances on the stability of emulsion systems

Dissertation solver: Mariana Dančíková, MSc
Supervisor: Hrádková Iveta, Assoc.Prof. MSc , PhD ( ive...@vscht.cz)

Anotation: The use of antimicrobial substances in cosmetic products is a frequently discussed topic in the connection with the use of the new substances, their toxicological profile and the influence on physical, chemical and microbiological stability of products.
The aim of thesis is the design of model cosmetic systems; the comparison of antimicrobial effect of selected antimicrobial compounds (commercial and newly synthesized) in model systems; the determination of skin penetration and potential for skin irritation of tested antimicrobial substances in different model systems by alternative toxicological method in vivo in system of reconstructed 3D models of human skin; the monitoring of physical-chemical stability of model cosmetic systems and formation of nitrosamines, formaldehyde and other toxic substance in dependence on chemical structure of biological active substances in model system.

Dependence of quaternary ammonium salts antimicrobial effect on their structure

Dissertation solver: Kateřina Sasínová, MSc
Supervisor: Hrádková Iveta, Assoc.Prof. MSc , PhD (iveta.hradkova@vscht.cz )
Berčíková Markéta. MSc , PhD

Anotation: Some of quaternary ammonium salts are used in the form of pure substance as disinfection substance in human and veterinary medicine (Ajatin, Septonex). Other quaternary ammonium salts in the form of technical mixture are used as surfactants with the antimicrobial and antistatic effect in the skin cleaning cosmetics. The antimicrobial effect can be enhanced by altering the structure of the molecule of substance.
In the theoretical part, find the quaternary ammonium salt in the literature, which are used as antimicrobial substances in medicine and cosmetics. Evaluate the literature data and suggest the synthesis of new quaternary ammonium salts, which would have higher antimicrobial effect.
In the experimental part of the work, synthesize several series of pure quaternary ammonium salts. Optimize their synthesis conditions. Determine their critical micellar concentration and antimicrobial effect and compare it with the effect of currently used quaternary salts.

Updated: 1.10.2024 08:59, Author: Jiří Štětina