• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 259
  • 176
  • 47
  • 33
  • 30
  • 30
  • 8
  • 5
  • 4
  • 4
  • 4
  • 4
  • 4
  • 4
  • 4
  • Tagged with
  • 691
  • 691
  • 325
  • 129
  • 89
  • 71
  • 63
  • 59
  • 59
  • 52
  • 51
  • 47
  • 43
  • 41
  • 39
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
531

Mikrobielle Exopolysaccharide von Milchsäurebakterien

Mende, Susann 22 October 2014 (has links) (PDF)
In der Milchindustrie spielt die Auswahl der Starterkulturen eine wichtige Rolle bei der Herstellung fermentierter Produkte mit gewünschter Textur und entsprechenden sensorischen Eigenschaften. Milchsäurebakterien mit der Fähigkeit extrazelluläre Polysaccharide (EPS) zu synthetisieren sind von besonderem Interesse, da auf Grund der in situ gebildeten Hydrokolloide der Einsatz von Zusatzstoffen vermieden werden kann. Die Wirkung von EPS auf die Produkt-eigenschaften ist in der Literatur bereits mehrfach beschrieben, wird jedoch auf Grund der Vielzahl an unterschiedlichen Stämmen und Fermentationsparametern bzw. einer fehlenden Systematisierung immer noch sehr kontrovers diskutiert. Des Weiteren stellt die wissenschaftliche Aufklärung der komplexen Struktur-Funktionsbeziehungen und der Wechselwirkungen mit anderen Produktkomponenten eine große Herausforderung dar. Um die Zusammenhänge besser verstehen zu können, wurde in dieser Arbeit ein neuer Ansatz gewählt: isolierte und aufgereinigte EPS wurden der Milch vor der Säuerung zugesetzt und die daraus hergestellten Milchgele mit jenen mit in situ produzierten EPS verglichen. In Milchgelen aus Einzelstammkulturen von Streptococcus thermophilus oder Lactobacillus delbrueckii ssp. bulgaricus wurden EPS‑Gehalte von 40 - 150 mg/kg ermittelt. Die Gele unterschieden sich hinsichtlich ihrer Viskosität und ihres fadenziehenden Charakters, was erste Hinweise auf die Art der gebildeten EPS liefert. Die Synthese größerer Mengen an EPS zur Charakterisierung und Untersuchung ihrer Funktionalität erfolgte entkoppelt von der Produkt­herstellung mit ausgewählten Stämmen in Batch-Fermentationen mit konstantem pH in komplexen oder semidefinierten Medien. S. thermophilus ST‑143 produzierte ~ 300 mg/L fadenziehende EPS, die durch entsprechende Aufreinigungsschritte als drei EPS‑Fraktionen gewonnen werden konnten: freie EPS (EPSf), kapsuläre EPS (EPSk) und ein Gemisch aus beiden (EPSf+k). EPSf haben eine höhere Molekülmasse (M = 2,6 x 10^6 Da) und eine höhere intrinsische Viskosität (1,14 mL/mg) im Vergleich zu EPSk (M = 7,4 x 10^3 Da, 1,4 x 10^5 Da; intrinsische Viskosität = 0,06 mL/mg) und führten bereits in geringen Mengen zu rheologischen Veränderungen. Allerdings scheinen die EPSk Wechselwirkungen zwischen EPSf Molekülen zu unterstützen. In chemisch gesäuerten Milchgelen konnte durch den definierten Zusatz aufgereinigter Fraktionen von EPSf und EPSf+k vor der Säuerung (c = 0 - 0,35 mg/g) erstmals eine konzentrationsabhängige Wirkung aufgezeigt werden. Mit EPSf stieg der maximale Speichermodul der Milchgele als Maß für die Gelsteifigkeit linear an (457 - 722 Pa). EPSk zeigten hingegen keinen Einfluss. Als Modellpolysaccharid wurde vergleichend das gut beschriebene, ebenfalls ungeladene und nicht gelbildende Homopoly­saccharid Dextran herangezogen (c = 0 - 300 mg/g). EPSf und Dextran veränderten die Gelbildung, erhöhten die Steifigkeit stichfester Gele und die Viskosität gerührter Gele in ähnlichem Maße, es waren jedoch deutlich unterschiedliche Konzentrationen notwendig. Die in den Milchgelen beschriebenen Einflüsse können unter anderem auf Depletionseffekte zwischen gleichgeladenen Polymeren (hier Proteine und Polysaccharide) zurückgeführt werden. / The selection of suitable starter cultures for the production of fermented milk with a desired texture and corresponding sensory attributes is of great importance for the dairy industry. Lactic acid bacteria with the ability to synthesise extracellular polysaccharides (EPS) are of particular interest, because these in situ produced hydrocolloids may allow to omit the use of additives. Many effects of EPS on product properties are already described in the scientific literature, but are still discussed controversially because of the multitude of different strains and fermentation parameters and, hence, a lack of systematisation. Furthermore, research on the mechanisms behind the structure-function relationship and interactions with other product components is a challenging area. To obtain a deeper understanding of this complex system, a new approach was chosen for the present study: EPS were isolated, purified and added to the milk prior to acidification, and the respective milk gels were compared with those with in situ produced EPS. In milk gels acidified by single strains of Streptococcus thermophilus or Lactobacillus delbrueckii ssp. bulgaricus, EPS contents of 40 - 150 g/kg were determined. The gels differed in viscosity and their ropy character, which is a first indicator for the type of the EPS. To allow for their chemical and technofunctional characterisation, the synthesis of higher amounts of EPS was performed by batch-fermentation at constant pH and decoupled from the product manufacturing with selected strains in complex or semidefined media. S. thermophilus ST‑143 synthesised ~ 300 mg/L ropy EPS, which were isolated as three different EPS fractions by applying particular purification steps: free EPS (EPSf), capsular derived EPS (EPSk) and a mixture of both EPS (EPSf+k). EPSf had a higher molecular mass (M = 2.6 x 10^6 Da) and a higher intrinsic viscosity (1.14 mL/mg) compared to EPSk (M = 7.4 x 10^3 Da, 1.4 x 10^5 Da; intrinsic viscosity = 0.06 mL/mg) and affected the rheological properties of aqueous solutions already at low concentration. However, EPSk appear to support interactions between the EPSf molecules. In chemically acidified milk gels a concentration dependent impact of EPSf and EPSf+k, which were added to the milk prior to acidification (c = 0 - 0,35 mg/g), was described for the first time. The maximum of the storage modulus as a measure for stiffness of the milk gels linearly increased with EPSf content (457 - 722 Pa). With EPSk no effects were observed. For the purpose of comparison dextran, a well described also uncharged and non gelling homopolysaccharide, was used as a model polysaccharide (0 - 300 mg/g). EPSf and dextran affected the gelation, increased gel stiffness of set gels and viscosity of stirred gels to a similar way, but the concentrations needed for that found to be completely different. The effects described for milk gels can be ascribed among others to depletion interactions between similar charged polymers (here proteins and polysaccharides).
532

Lizocimo įtaka pieno technologinėms savybėms / The Influence of Lysozyme on the Milk Technological Properties

Šapošnikova, Jelena 06 June 2006 (has links)
Work size - 60 pages, including 35 pictures, 1 table. List of literature - 44 sources. The beginning of the work -2004 09 01, the end of the work - 2006 05 15. Purpose of work: To explore, what influence the additive lysozyme on technological properties of milk which are important in manufacture of fermental cheeses and sour - milk products has. In work presents the analysis of lysozyme influence on the technological properties of. The results show that lysozyme prevent to develop of undesirable microorganisms and positively influences on the quality of fermented milks. It was established that the additive of lysozyme prolongs the duration of the bactericidal phase. The investigation of the rennet formation time has shown that the clothing of the milk in samples with lysozyme formed 12 - 15  faster as in compared with the control sample without lysozyme. Besides, it is established, that the additive of lysozyme intensifies the process removal of the whey. The research investigation show that in samples with lysozyme, whey distinguish in smaller optical density as compared with control samples. The development of lactic bacteria during fermentation process was examined too. It was found that lysozyme influence on this process is very insignificant. It was established that the additive of lysozyme insignificant reduces viscosity and acidity of fermented milk gels.
533

Engineering of Lactic Acid Bacteria strains modulating immune response for vaccination and delivery of therapeutics

Azevedo, Marcela 25 October 2013 (has links) (PDF)
The use of Lactic Acid Bacteria (LAB), such as Lactococcus lactis (LL), as DNA delivery vehicles represents an interesting strategy as they are regarded as safe. Wild type (wt) LL or recombinant invasive LL, were able to trigger DNA expression by epithelial cells both in vitro and in vivo. However, important information about how LL can transfer DNA plasmids is still missing. Therefore, we decided to construct a new recombinant invasive LL strain expressing mutated Internalin A (mInlA) from the pathogen Listeria monocytogenes to understand the manner by which the DNA is transferred to mammalian cells. mInlA expression was detected by FACS analysis and LL-mInlA strain showed to be more invasive than the wt strain after co-incubation assays with non-confluent or polarized intestinal epithelial cells (IECs). Confocal microscopy confirmed the invasive status of LL-mInlA which demonstrated to deliver more efficiently the eukaryotic expression vector coding the allergen β-lactoglobulin, pValac:BLG, in vitro to IECs and to dendritic cells (DCs). LL-mInlA was also capable to transfer pValac:BLG to DCs across a monolayer of differentiated IECs. In vivo, invasive lactococci tended to increase the number of mice expressing BLG. Moreover, noninvasive or invasive LL-mInlA stimulated the secretion of the pro-inflammatory cytokine IL-12 in DCs and, in vivo, after oral or intranasal immunization trials, non-invasive LL polarized the immune response more in the type 1 direction while invasive LL generated a Th2-type response in immunized animals. All these data gives new insights on the mechanism of lactococci uptake for delivery of therapeutics.
534

Ottimizzazione di pratiche enologiche per la riduzione di contaminanti biologici in vino / OPTIMIZATION OF OENOLOGICAL PRACTICES TO REDUCE BIOLOGICAL CONTAMINANTS IN WINE

MONCALVO, ALESSANDRO 21 February 2013 (has links)
L’ocratossina e le ammine biogene sono due metaboliti biologici che possono essere ritrovati nei vini. Il primo di questi contaminanti è stato studiato recentemente per la sua elevata tossicità sebbene non sia rintracciabile frequentemente nei vini. Le ammine biogene sono presenti in ogni tipo di vino in differenti concentrazioni, oltretutto, alcune di loro, ad alte concentrazioni, possono causare reazioni allergiche. Gli obiettivi di questo PhD riguardano tre differenti aspetti. Indagare metodi biologici di per la decontaminazione di ocratossina A durante la vinificazione; in particolare lo studio si è focalizzato sull’uso di un ceppo Lactobacillus plantarum utilizzato come starter malolattico. Valutare la presenza di Lactobacillus spp., isolati da mosto e vino, in grado di produrre ammine biogene, usando tecniche molecolari come la reazione a catena della polimerasi (PCR) per rilevare i geni codificanti gli enzimi responsabili della sintesi di questi composti. Testare la capacità di un L. plantarum di effettuare la malolattica effettuando l’inoculo in differenti fasi della vinificazione e valutare il trend delle ammine biogene già presenti nel mosto. / Two of the major biological metabolites present in wine are the ochratoxin and the biogenic amines. The first of these contaminants was studied in recent decades because of its toxicity in humans, although its presence is not frequent in wines. The biogenic amines are present in every types of wine in different concentration, and some of them, in high concentrations, can cause allergenic reactions in humans. The objectives of this PhD regard three different aspects. Investigate the biological methods to reduce ochratoxin A in wine during winemaking; in particular the study is focused to use a Lactobacillus plantarum strain as malolactic starter. Investigate the presence of Lactobacillus spp., isolated from must and wine, able to produce the amines, using molecular techniques as polymerase chain reaction (PCR) to detect the genes that encode for the enzymes responsible of the synthesis of these compounds. Test the ability of a L. plantarum to perform MLF in relationship with inoculation time and assess the trend of biogenic amines already present in must.
535

Materials and microfabrication approaches for completely biodegradable wireless micromachined sensors

Luo, Mengdi 12 January 2015 (has links)
Implantable sensors have been extensively investigated to facilitate diagnosis or to provide a means to generated closed loop control of therapy by yielding in vivo measurements of physical and chemical signals. Biodegradable sensors which degrade gradually after they are no longer functionally needed exhibit great potential in acute or shorter-term medical diagnostic and sensing applications due to the advantages of (a) exclusion of the need to a secondary surgery for sensor removal, and (b) reduction of the risk of long-term infection. The objective of this research is to design and characterize microfabricated RF wireless pressure sensors that are made of completely biodegradable materials and degrade at time-controlled manner (in the order of years and months). This was achieved by means of investigation of appropriate biodegradable materials and development of appropriate fabrication processes for these non-standard (Microelectromechanical systems) MEMS materials. Four subareas of research are performed: (1) Design of sensors that operate wirelessly and are made of biodegradable materials. The structure of the wireless sensor consists a very compact and relatively simple design of passive LC resonant circuits embedded in a polymer dielectric package. To design the sensor with a particular resonant frequency range, an electromagnetic model of the sensor and a mechanical model for circular plate are developed. The geometry of the sensor is established based on the analytical and finite element simulations results. (2) Investigation of the biodegradable materials in the application of implantable biodegradable wireless sensors to achieve controllable degradation lifetimes. Commercially available and FDA approved biodegradable polymers poly(L-lactic acid) (PLLA) and a "shell-core" structure of poly(lactic-co-glycolic acid) (PLGA) and polyvinyl alcohol (PVA) are utilized as the dielectric package for slow and rapid degradation sensors, respectively. Biodegradable metallic zinc and zinc/iron couples are chosen as conductor materials. The degradation behavior of Zn and Zn/Fe-couple are investigated in vitro. (3) Development of novel fabrication processes. The process exploit the advantages of MEMS technology in fabricating miniaturized devices, while protecting vulnerable biodegradable materials from the strong and/or hazardous chemicals that are commonly used in conventional MEMS fabrication process. These new processes enable the fabrication of biocompatible and biodegradable 3-D devices with embedded, near-hermetic cavities. (4) Testing the pressure response functionality and studying the degradation behavior of the wireless biodegradable pressure sensors. Both PLLA-based and PLGA/PVA-based sensors are characterized in vitro by being immersed in 0.9% saline for prolonged time. All the sensors exhibit three stages of behavior in vitro: equilibration, functional lifetime, and performance degradation. During the functional lifetime, most sensors exhibit fully stable functionality. The PLLA-based sensors show no significant weight loss within 8 month and are expected to fully degrade after 2 years, while the PLGA/PVA-based sensors can degrade completely within 26 days.
536

Fermentuotų augalų produktų panaudojimas mėsos pusgaminių gamyboje / The use of ferment plant products in the production of meat ready-to-cook

Augėnienė, Dovilė 18 June 2013 (has links)
Šio darbo tikslas: nustatyti kietafaze fermentacija fermentuotų topinambų ir lubinų raugų įtaką mėsos pusgaminių kokybei ir saugai Darbo uždaviniai: Įvertinti kietafaze fermentacija (toliau – KF) fermentuotų skirtingomis pienarūgštėmis bakterijomis topinambų įtaką: kiaulienos pusgaminių fizikiniams – cheminiams rodikliams; jautienos pusgaminių fizikiniams – cheminiams rodikliams; lakiųjų junginių pokyčiams jautienos pusgaminiuose. Įvertinti KF fermentuotų skirtingomis pienarūgštėmis bakterijomis lubinų įtaką: kiaulienos pusgaminių fizikiniams – cheminiams rodikliams; jautienos pusgaminių fizikiniams – cheminiams rodikliams; lakiųjų junginių pokyčiams kiaulienos ir jautienos pusgaminiuose. Įvertinti KF fermentuotų skirtingomis pienarūgštėmis bakterijomis topinambų ir lubinų įtaką kiaulienos pusgaminių bendram bakteriniam užterštumui. Eksperimentui atlikti buvo gaminami kiaulienos ir jautienos pusgaminiai su 5 proc. raugu (fermentuotais lubinais ir topinambais, fermentacijai panaudojant tris pienarūgštes bakterijas: P. acidilactici KTU -05-7, P. pentosaceus KTU -05-8, L. sakei KTU -05-6). Naudota metodika: LST ISO 1442:2000 „Mėsa ir mėsos produktai. Drėgmės kiekio nustatymas (pamatinis metodas).; Grau ir Hammo (1956) metodas (vandens rišlumo nustatymas); Soksleto (1879) metodas (riebalų kiekio nustatymas); LST ISO 936:2000 „Mėsa ir mėsos produktai. Bendrojo pelenų kiekio nustatymas; lakiųjųi junginių analizė atlikta dujų chromatografu metodu. Išvados: Fermentuoti lubinų... [toliau žr. visą tekstą] / The aim of this paper is to identify the solid state fermentation of Jerusalem artichoke and lupine cultures affect to the quality and safety of meat ready-to-cook. Job tasks: Evaluate the solid state fermentation (thereinafter – SSF) fermente by lactic acid bacteria (thereinafter – LAB) in different Jerusalem artichoke influence: pork ready-to-cook physical- chemical parameters; beef ready-to-cook physical-chemical parameters; changes of volatile compounds in beef ready-to-cook. Evaluate the SSF of fermented in different LAB lupine influence: pork ready-to-cook physical- chemical parameters; beef ready-to-cook physical-chemical parameters; changes of volatile compounds in pork and beef ready-to-cook. Evaluate SFF ferment in different LAB Jerusalem artichoke and lupine influence to pork ready-to-cook impurity. In this experiment pork and beef ready-to-cook have been used with 5 percent product (fermented lupine and Jerusalem artichoke, for fementation were used 3 LAB: P. acidilactici KTU -05-7, P. pentosaceus KTU -05-8, L. sakei KTU -05-6). Methods: LST ISO 1442:2000 Meat and meat products – Determination of moisture content (References method).;Grau and Hamm (1956); Soxlet (1879); LST ISO 936:2000 Meat and meat products – Determination of total ash.; Detection volatile compounds using gas chromatography method. Conclusion: Ferment lupine and Jerusalem artichoke products have reduced pH in pork and beef ready-to-cook. Beef ready-to-cook fermentated with Jerusalem artichoke... [to full text]
537

Bakteriocinus produkuojančių pieno rūgšties bakterijų panaudojimo galimybės daržovių biokonservavimui / The usability of lactic acid bacteria producing bacteriocins for vegetable biopreservation

Jankauskaitė, Skaistė 18 June 2014 (has links)
Tikslo įgyvendinimui buvo atlikta baltagūžių ir mėlynųjų kopūstų bei saldžiųjų raudonųjų ir geltonųjų paprikų fermentacija skirtingomis pieno rūgšties bakterijomis (PRB) (L. sakei, P. pentosaceus KTU-08, P. pentosaceus KTU-09 ir P. acidilactici). Tiriant fermentacijos proceso efektyvumą buvo įvertinta pH dinamika, gautuose produktuose nustatytas PRB kolonijas sudarančių vienetų skaičius grame produkto (KSV/g), L (+) ir D-(-) pieno rūgšties izomerų kiekis, atlikta juslinė analizė, priimtiniausiems produktams įvertintos spalvų koordinatės ir tekstūros savybės. Pagal gautus tyrimų rezultatus galima teigti, kad eksperimente naudotos PRB yra tinkamos baltagūžių ir mėlynųjų kopūstų bei saldžiųjų raudonųjų ir geltonųjų paprikų fermentacijai. PRB taikymas daržovių fermentavimui yra efektyvus, nes į smulkintas daržoves įterpus PRB, jos kurį laiką dominuoja. Naudojant fermentacijai PRB, gaunamas pakankamai žemas produktų pH, o tai suteikia fermentuotoms daržovėms priimtinas vartotojams juslines savybes. Daržovių fermentacijai taikant PRB, gaunami didesnio šviesumo, raudonumo, geltonumo, grynumo bei spalvos tono produktai. Siekiant užtikrinti fermentuotų produktų saugą D(-) pieno rūgšties izomerų aspektu daržovių fermentacijai reikėtų rinktis L. sakei. / Fermentations with different lactic acid bacteria (LAB) (L. sakei, P. pentosaceus KTU-08, P. pentosaceus KTU-09 and P. acidilactici) of white cabbage, red cabbage, sweet red and yellow paprika were performed in order to achieve the goal. While studying the effectiveness of the fermentation process, pH dynamics was evaluated, colony forming units of LAB in fermented products, concentration of lactic acid isomers L (+) and D(-), sensory analysis, colour coordinates and texture parameters were evaluated. We conclude that in the experiment used LAB are suitable for the fermentation of a white cabbage, red cabbage, sweet red and yellow paprika. The application of LAB is effective, because LAB were dominate for some time in the fermented vegetables. While using LAB for the vegetables fermentation, pH was found quite low, and improve sensory properties of the fermented vegetables products. LAB gives higher brightness, clarity of red and yellow, as well as colour tone of the fermented products. In order to ensure the safety of fermented products, in the context of D (-) lactic acid, L. sakei would be more suitable for the vegetable fermentation.
538

Apsauginių kultūrų panaudojimas mėsos pusgaminių gamyboje / The use of protective cultures in the manufacture of semi-finished meat

Razutytė, Orinta 18 June 2014 (has links)
Darbo tikslas: ištirti apsauginių kultūrų panaudojimo mėsos pusgaminių gamyboje galimybes, gerinant saugą ir kokybę. Darbo uždaviniai: įsisavinti apsauginių kultūrų panaudojimo mėsos pusgaminių gamyboje būdus, pusgaminių kokybinių ir saugos rodiklių nustatymo metodus; ištirti apsauginių bakterijų kultūrų: Lactobacillus spp. Staphylococcus xylosus, poveikį mėsos pusgaminių mikrobiologiniams ir fizikiniams cheminiams rodikliams, įvertinti jų saugą ir kokybę; ištirti termiškai apdorotų mėsos pusgaminių su apsauginėmis bakterinėmis kultūromis Lactobacillus spp., Staphylococcus xylosus juslines savybes; palyginti įprastų ir gautų mėsos pusgaminių su apsauginėmis kultūromis kokybę ir saugą, juslines savybes, vartojimo terminą; apdoroti statistiškai gautus duomenis, apibendrinti rezultatus ir pateikti išvadas. Rezultatai: priedas su apsauginėmis kultūromis Lactobacillus spp., Staphylococcus xylosus visiškai išnaikino E. Coli jautienos farše, supakuotame į vakuuminę pakuotę (p ≤ 0,01), modifikuotų dujų atmosferą (p ≤ 0,01), laikomo aerobinėmis sąlygomis (p ≤ 0,001) lyginant su kontrole. Apsauginių kultūros ženkliai sumažino bendrą aerobinių mikroorganizmų skaičių lyginant su kontrole (p ≤ 0,001). Apsauginių kultūrų įterpimas sumažino biogeninių aminų tiramino, spermidino ir spermino kiekius iki mažesnių už aptikimo ribą kiekių (< 5 mg/kg), tačiau mėginiuose su apsauginių kultūrų priedu, laikomuose aerobinėmis sąlygomis, nustatytas padidėjęs fenilalanino kiekis, lyginant su kontrole... [toliau žr. visą tekstą] / The aim of the work was to investigate the possibilities of using protective cultures in the manufacture of semi-finished meat in improving safety and quality. The tasks of the work were to master ways of using protective cultures in production of semi-finished meat; methods for determining quality and safety indicators of semi – finished meat; to investigate the impact of protective bacterial cultures: Lactobacillus spp., Staphylococcus xylosus to microbiological and physico-chemical parameters of semi – finished meat in order to ensure their safety and quality; to investigate organoleptic properties of the heat-treated semi – finished meat with a protective bacterial cultures Lactobacillus spp., Staphylococcus xylosus; to compare quality and safety, organoleptic characteristics, expiry date of conventional and meat preparations with protective cultures; to process statistically obtained data, summarize the results and present findings. Results: • Additive with protective cultures Lactobacillus spp., Staphylococcus xylosus completely destroyed E. coli in vacuum packed minced beef (p ≤ 0,01), in modified gas atmosphere (p ≤ 0,01), stored under aerobic conditions (p ≤ 0,001) compare with the controls. • Protective cultures significantly reduced the total number of aerobic microorganisms compare with controls (p ≤ 0,001). • Insertion of protective cultures reduced biogenic amines tyramine, spermidine and spermine below the detection limit (<5 mg / kg), however, samples... [to full text]
539

Biochemical And Genetic Studies On The Pyruvate Branch Point Enzymes Of Rhizopus Oryzae

Acar, Seyda 01 January 2004 (has links) (PDF)
Rhizopus oryzae is a filamentous fungi which produces lactic acid and ethanol in fermentations. R. oryzae has numerous advantages for use industrial production of L-(+)-lactic acid but the yield of lactic acid produced on the basis of carbon consumed is low. Metabolic flux analysis of R. oryzae has shown that most of the pyruvate produced at the end of the glycolysis is channelled to ethanol, acetyl-CoA and oxaloacetate production. This study aimed to answer some questions addressed on the regulation of pyruvate branch point in R. oryzae and for this purpose biochemical characterisation of the enzymes acting at this branch point and cloning the genes coding for these enzymes have been done. Pyruvate decarboxylase was purified and characterised for the first time from R. oryzae. The purified enzyme has a Hill coefficient of 1.84 and the Km of the enzyme is 8.6 mM for pyruvate at pH 6.5. The enzyme is inhibited at pyruvate concentrations higher than 30 mM. The optimum pH for enzyme activity shows a broad range from 5.7 and 7.2. The monomer molecular weight was estimated as 59&plusmn / 2 kDa by SDS-PAGE analysis. Pyruvate decarboxylase (pdcA and pdcB) and lactate dehydrogenase (ldhA and ldhB) genes of R. oryzae have been cloned by PCR-cloning approach and the filamentous fungi Aspergillus niger was transformed with these genes. The A. niger transformed with either of the ldh genes of R. oryzae showed enhanced production of lactic acid compared to wild type. Citric acid production was also increased in these transformants while no gluconate production was observed Cloning of hexokinase gene from R. oryzae using degenerate primers was studied by the use of GenomeWalker kit (Clontech). The results of this study were evaluated by using some bioinformatics tools depending on the unassembled clone sequences of R. oryzae genome.
540

Organische Linkermoleküle auf Basis natürlicher Hydroxycarbonsäuren zum Aufbau homochiraler poriger Festkörperstrukturen

Eißmann, Diana 10 October 2011 (has links) (PDF)
Das Ziel dieser Arbeit bestand in der Synthese neuartiger homochiraler Molekülstrukturen, welche nach Konzepten des Crystal Engineering über ein starres Grundgerüst sowie koordinationsfähige Haftgruppen verfügen sollten. Unter Verwendung von Wein- und Milchsäure, als Vertreter der natürlich vorkommenden, enantiomerenreinen α-Hydroxycarbonsäuren, konnten die entsprechenden Derivate mit aromatischen und/oder acetylenischen Spacerelementen hergestellt und umfassend charakterisiert werden. Die synthetisierten Wein- und Milchsäureverbindungen sowie die sich von den jeweiligen Weinsäureestern ableitenden TADDOLe wurden außerdem auf ihre optische Aktivität, ihre Affinität gegenüber verschiedenen Lösungsmitteldämpfen, ihr Einschlussverhalten gegenüber achiralen und chiralen Lösungsmitteln sowie ihre Eignung als organische Linker bei der Synthese von metallorganischen Gerüststrukturen untersucht. Mittels Röntgeneinkristallstrukturanalyse konnten die Festkörperstrukturen einiger Derivate aufgeklärt und diese hinsichtlich ihrer Konformation verglichen werden.

Page generated in 0.0681 seconds