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Microrheology of Biocolloids
Hnyluchová, Zuzana ; Omelka, Ladislav (referee) ; Kráčalík, Milan (referee) ; Pekař, Miloslav (advisor)
The main aim of the doctoral thesis was study of passive microrheological techniques as advanced methods for characterisation of viscoelastic properties of soft material. These techniques are able to provide certain advantaged or additional information on classical rheology. Several techniques from the wide range of passive microrheological group such as one particle video – microrhelogy with IDL data procesing, microrheology based on light scattering – DLS or FCS microrheology have been applied in practice during my PhD studies. New Matlab script has been also invented to simply obtain information about viscosity of low volume samples. Aplicability of techniques were studied on several various bicolloids such as solutions or gels of hyaluronic acid, on study of properties at the interfaces or on gelation proces studies of agarose. Obtained data were compared classical rheology results. Suitability of each technique for investigated systems or appropriate reccomendations for further measurements were didcussed based on obtained data. Main advantages and limites of passive microrheology techniques were also described in comparison wih classical rheology method.
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Spin-trapping of radical products of H-transfer from oxygeneous donors
Šafaříková, Lenka ; Polovka, Martin (referee) ; Omelka, Ladislav (advisor)
Within the bachelor thesis the evaluation of experimental material focused on EPR study of spin-trapping of phenoxyl radicals on aromatic nitrosocompounds was performed. It was found that phenoxyl radicals from unhindered phenols add to nitrosogroup in the ortho-position. As a result, the nitroxyl radicals are formed. According to the structure of nitrosocompounds this nitroxyl radicals have the character either of phenoxazinoxyl radicals in the case of nitrosobenzene or derivatives of diphenylnitroxyl radical in the case of nitrosoduren. In the work is also documented the specific behavior of some phenols containing methyl group as the para substituent.
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Study of qualitative parameters of fruit juices and possibilities of their modification via technological modifications
Fajtl, Zdeněk ; Omelka, Ladislav (referee) ; Polovka, Martin (advisor)
Ovocné šťávy jsou celosvětově nejoblíbenějšími nealkoholickými nápoji. Kromě vitamínů a minerálů jsou také bohatým zdrojem polyfenolů, které jsou považovány za látky přispívající k celkové antioxidační aktivitě. Zvyšující se požadavky konzumentů na kvalitu a bezpečnost potravin nutí výrobce k zvyšování výrobních a kvalitativních standardů potravin. Nedávné inovace ve výrobě ovocných šťáv vedly k modifikacím výrobních podmínek, které zahrnují změny ve složení šťávy (např. přídavek ovocné dužiny nebo malých ovocných kousků), vylepšování vlastností obalových materiálů a modifikace produkční atmosféry. Cílem diplomové práce bylo pomocí metod EPR a UV-VIS spektroskopie posoudit vliv různých výrobních postupů na vybrané kvalitativní znaky (antioxidační aktivita, změna barvy a koncentrace vybraných fytochemikálií) pomerančových šťáv s dužinou a ananasových šťáv, a charakterizovat jejich změny v průběhu dlouhodobého skladování. Získané výsledky byly zpracovány metodami multivariační statistické analýzy s cílem posoudit vliv původu suroviny, roku produkce a použitých výrobních podmínek na sledované parametry a celkovou kvalitu ovocných džusů. Výsledky jasně prokázaly, že pasterizace ovlivňuje kvalitu výrobku; ačkoli byla použita „šetrná“ pasterizace, byl u těchto vzorků pozorován mírný pokles prakticky všech monitorovaných parametrů v porovnání s čerstvými – nepasterizovanými šťávami. Avšak pokud jde o po-pasterizační změny, byl prokázán významný vliv produkční atmosféry na monitorované kvalitativní parametry šťáv, prokazující, že náhrada kyslíku inertními plyny může výrazně prodloužit trvanlivost šťáv. Kinetické studie změn sledovaných parametrů na době skladování ukazují, že ve většině případů dochází k postupnému zhoršování všech monitorovaných parametrů, a to bez ohledu na technologii zpracování šťávy. Ve vzorcích vyrobených použitím modifikované atmosféry bylo, v závislosti na typu inertního plynu, pozorováno zpomalení poklesu jednotlivých kvalitativních parametrů šťáv jako výsledek aplikace inertní atmosféry. Tento trend byl zřejmý především pro delší skladovací období, zatímco na začátku skladování (6 - 7 týdnů po výrobě dané šťávy) byly pozorované trendy nejednoznačné. Lze proto předpokládat že tento „ochranný“ efekt inertní atmosféry je ovlivňován fyzikálně-chemickými vlastnostmi jednotlivých plynů, zejména jejich rozpustností v kapalném médiu. Výsledky také prokázaly že vlastnosti šťáv jsou ,bez ohledu na druh ovoce, výrazně ovlivňovány také sezónními vlivy a původem surové šťávy. Z výsledků statistické analýzy vyplývá, že rok výroby je silným diskriminačním faktorem. Na základě všech monitorovaných charakteristik, bylo dosaženo absolutní diskriminace vzorků pomocí kanonické diskriminační analýzy. Pokud jde o původ surovin, byla dosažena pouze částečná diferenciace, i když s poměrně vysokým klasifikačním skóre. Pokud jde o technologii výroby, byla dosažena pouze částečná diferenciace vzorků podle typu použitého inertního plynu. Získané poznatky pomohou výrobcům ovocných šťáv s optimalizací výrobních podmínek s cílem získat výrobek s maximem prospěšných vlastností, které by si udržel po celou dobu expirace, jejíž délka může být také optimalizovány na základě prezentovaných výsledků.
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Spin-trapping of radical products of H-transfer from carboneous donors
Krkošková, Petra ; Polovka, Martin (referee) ; Omelka, Ladislav (advisor)
On example of special type of a coumarine derivatives and also compounds with character of esters and diesters, which have an –CHR- group between two carbonyl groups or between carbonyl and imino group, the possibility of detection of C-radicals resulting from the homolytic splitting of the C-H bond of a methylene group was studied. PbO2 was used as an appropriate compound, on which surface the coumarine derivatives and the other compounds are decomposed. C-radicals were investigated by means of technique of spin-trapping and by comparison of experimental and simulated EPR spectra.
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In vitro study of antioxidant activity of food supplements
Vopelková, Dominika ; Pořízka, Jaromír (referee) ; Omelka, Ladislav (advisor)
Bachelor thesis deals with the determination of antioxidant activity of food supplements in vitro. The theoretical part focuses on legislative requirements of food supplements, their characteristic and classification. Further, the attention is also devoted to antioxidants, their properties, effects, importance and utilization. Separate chapter describes herbs, which are an essential component of researched supplements, their effects and properties. For experimental part several food supplements in various forms (capsule, tea, juice, dried fruits) were chosen and total content of polyphenols was determined using the UV-VIS spectroscopy. Further, the total antioxidant activity is characterized by electron paramagnetic resonance involving DPPH method.
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Microorganisms with lipoplytic activity and their applications
Pavlačková, Jana ; Omelka, Ladislav (referee) ; Omelková, Jiřina (advisor)
Lipases are hydrolytic enzymes that are produced by many types of microorganisms. This thesis describes not only the microorganisms which produce lipases but also different possibilities for the industrial utilization of lipases. Lipases are widely used in reactions where the combination of a lipophilic substrate with a hydrophilic one is necessary – in the synthesis of ascorbic acid fatty esters, sugar esters, lipoaminoacids and in the lipophilization of phenolic derivatives. Lipases are also important in relation to environmental protection. For example, they are used for the purification of waste water. In this thesis, five different preparations containing microorganisms with lipolytic activity were tested for lipolytic activity. There are many ways of determining lipolytic activity. The spectrophotometric determination of lipolytic activity that uses the ability of lipases to divide p-nitrophenyllaurate to p-nitrophenol may serve as an example. After this p-nitophenol is detected spectrophotometricaly.
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Modern Approaches in Qualitative Aspects of Foods Assessment
Tobolková, Blanka ; Omelka, Ladislav (referee) ; Rapta, Peter (referee) ; Buňka, František (referee) ; Polovka, Martin (advisor)
Antioxidant properties and some other characteristics of selected organic and conventional products (wine, spelt flours) were evaluated in view of their potential utilization as markers suitable for food unambiguous differentiation according to the affiliation to production system. Beside these, study of fruit juices stability during storage in dependence on different technological procedures of juice processing was performed. In both cases, combination of dominantly EPR and UV/VIS spectroscopy but also other methods (e.g., HPLC, AAS, electrophoresis) was applied to evaluate the stability and antioxidant properties of selected samples. Statistical methods, especially methods of multivariate statistics were used to assess the influence of production and technological-processing operations on antioxidant status of foods and their selected characteristics. Qualitative analysis of Slovak and foreign organic and conventional wines proved that their antioxidant properties are influenced by production system, vintage and variety. On the basis of statistical analysis, descriptors of AAE, kTEMPOL and %RS were selected as the most powerful markers for Slovak organic and conventional wines discrimination. The discrimination of white and red organic and conventional wines possessed 100% and 95.2% correctness, respectively. High correctness of differentiation of Slovak and foreign wines was also achieved. Monitored descriptors of antioxidant activity of spelt flours varied in dependence on season, origin, variety, production system and depend also on way of spelt treatment, although this effect is not so significant. It was also confirmed that the type of extraction agent substantially affects the composition of extracts including polyphenols and flavonoids concentration, affecting thus also their antioxidant activity. Mixture of 50% ethanol/water was selected as the most promising extraction system. Although the results of individual spectroscopic assays revealed high variability and often ambiguous trends, the differences found were sufficient for successful differentiation of both wines and spelt flour samples according to the selected criteria by multivariate statistical processing of the data. Influence of changes in technological procedures of fruit juice processing (nitrogen atmosphere application, utilization of caps with oxygen scavengers) on radical-scavenging properties of 100% pineapples juices with pieces of pineapple and 100% orange juices with pulp was assessed as well. Results obtained proved that antioxidant activity of juices varied in dependence on storage conditions (temperature, storage time, light exposure) and depends also on origin, variety and quality of fruit used. However, the application of nitrogen atmosphere and active packaging materials is not sufficient enough to eliminate the oxidation reactions in juices, but changes in antioxidant activity are better predictable. It can be concluded that EPR spectroscopy could be effectively applied for wines and spelt flours differentiation according to the way of production and to assess the stability of food products, either alone or in combination of UV/VIS spectroscopy and the other methods, utilizing multivariate statistics for processing of experimental data.
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Microrheology of Biocolloids
Hnyluchová, Zuzana ; Omelka, Ladislav (referee) ; Kráčalík, Milan (referee) ; Pekař, Miloslav (advisor)
The main aim of the doctoral thesis was study of passive microrheological techniques as advanced methods for characterisation of viscoelastic properties of soft material. These techniques are able to provide certain advantaged or additional information on classical rheology. Several techniques from the wide range of passive microrheological group such as one particle video – microrhelogy with IDL data procesing, microrheology based on light scattering – DLS or FCS microrheology have been applied in practice during my PhD studies. New Matlab script has been also invented to simply obtain information about viscosity of low volume samples. Aplicability of techniques were studied on several various bicolloids such as solutions or gels of hyaluronic acid, on study of properties at the interfaces or on gelation proces studies of agarose. Obtained data were compared classical rheology results. Suitability of each technique for investigated systems or appropriate reccomendations for further measurements were didcussed based on obtained data. Main advantages and limites of passive microrheology techniques were also described in comparison wih classical rheology method.
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EPR Study of Radical Reactions of Secondary Amines in Liquid Phase
Šafaříková, Lenka ; Lehocký,, Marián (referee) ; Mazúr, Milan (referee) ; Omelka, Ladislav (advisor)
In the framework of Ph.D. thesis the evaluation of radical reactions of four groups of secondary amines R1–NH–R2 in the presence of some selected types of agents was performed using EPR spectroscopy. First group was represented by peroxoagents (3-chloroperbenzoic acid, tBuO2 radicals), the second group involved compounds of PbIV+ (PbO2, Pb(OAc)4) functioning as hydrogen-abstracting agents. In the presence of peroxyagents the formation of corresponding aminoxyl radicals R1–NO–R2 was demonstrated. In the case of surplus of tBuO2 radicals these radicals enter the consecutive reactions which products are new types of secondary aminoxyls. By the interpretation of reaction mechanism the intermediary formation of nitrones was assumed. These function in later steps of the reaction as spin traps for tBuO2 radicals. By the study of radical mechanism of amines R1–NH–R2 initiated by PbIV+ agents was proved, that these compounds hydrogen atom not only from –NH– group under formation of aminyl radicals, but also from C–H bonds in substituents R1, R2 (the formation of C-radicals). Because both groups of the radicals formed are characterized by high reactivity, their identification was possible only using spin-trapping method. In the course of the investigation of radical reactions of secondary amines the big amount of experimental EPR spectra was obtained. These exhibited in many cases very high hyperfine structure. Due to this fact it was necessary to perform the detailed evaluation on the basis of spectral simulation. Except of some special cases using this approach the interpretation of majority of registered EPR spectra was interpreted and EPR parameters were summarized in tables.
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