Orientador: Celio Kenji Miyasaka / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-03T20:55:28Z (GMT). No. of bitstreams: 1 Silva_LucianoBrunodeCarvalho_M.pdf: 1363000 bytes, checksum: e8be41339935878e0220e14d99b01b70 (MD5) Previous issue date: 2004 / Resumo: A degradação oxidativa dos ácidos graxos da soja, ocorrida durante o processamento dos grãos, desenvolve o sabor de feijão verde ou de soja crua que altera a palatabilidade e conseqüentemente aceitabilidade dos produtos à base de soja, resultando em problemas para a indústria. A enzima lipoxigenase (linoleato: O2 oxirredutase, EC 1.13.11.12), catalizadora dessa reação, está presente na soja sob a forma de três isoenzimas caracterizada por três genes dominantes, LOX-1, LOX-2 e LOX-3. O objetivo do presente trabalho foi a identificação e determinação qualitativa e quantitativa das frações de lipoxigenases em sementes de soja Glycine Max provenientes da quarta geração do primeiro retrocruzamento (F4) dos mutantes isentos das respectivas LOX {PI-408251 (-LOX-1), PI-86023 (-LOX-2), TOHOKU nº 74 (-LOX- 3)}, com o cultivar comercial IAC-8, resultando nas linhagens IAC 97-3503, IAC 97- 3512, IAC 97-3545 e IAC 97-3803, fornecidas pelo Instituto Agronômico de Campinas (IAC). A análise qualitativa e quantitativa destes quatro genótipos e do IAC 8-2 foi realizada através de 1) Eletroforese em gel de poliacrilamida contendo SDS, para discriminar as bandas existentes; 2) Teste colorimétrico e; 3) Determinação da atividade enzimática em espectrofotometria na presença de: 3.1)substratos específicos e, 3.2) reação acoplada de descoramento do b-caroteno. Observou-se por eletroforese em gel as bandas correspondentes a cada isoenzima. A reação de oxidação da LOX sobre o b- caroteno (LOX-3) e azul de metileno (LOX-2 e LOX-1) foi sensível para a detecção da LOX-1 e LOX-3. O método de determinação de atividade enzimática com a utilização de substratos específicos (ácido linoléico para LOX-1 e LOX-3, e metil-linoleato para LOX- 2) também foi sensível somente para a detecção de LOX-1 e LOX-3. Através da reação de cooxidação do b-caroteno pela LOX-2 e LOX-3 foi possível determinar todas as isoenzimas, complementando os resultados obtidos através da eletroforese em gel de poliacrilamida. Constatou-se que através dos cruzamentos e retrocruzamentos realizados pelo IAC, na linhagem IAC 97-3503 não demonstrou atividade de LOX-1, não tendo ocorrido redução significativa (p<0,05) nos outras três linhagens estudadas. Evidenciou-se redução significativa (p<0,05) da LOX-2 nas linhagens IAC 97-3512 e IAC 97-3545, quando comparados ao padrão IAC 8-2. Para a LOX-3 ocorreu redução significativa (p<0,05) no cultivar IAC 97-3503, não ocorrendo diminuição nas outras três linhagens em estudo / Abstract: The oxidative degradation of the soybean fatty acids which has taken place at the grain processing, have developed the flavor of green been or raw soybean. This degradation alters the palatability and consequently the acceptability of the products made by soybean, resulting in some industries problems. The lipoxygenase enzyme (linolenato: O2 oxirredutase, EC 1.13.11.12), which is the component that catalyze the reaction, exists in soybean in the shape of 3 isoenzymes characterized by 3 dominant genes, LOX-1, LOX-2 and LOX-3. The main propose of this work was the identification and qualitative and quantitative determination of the lipoxygenase fractions in Glycine max soybean seeds, which had come from the fourth generation of the first crossing (F4) of the mutants that didn¿t have the respective LOX {PI-408251 (-LOX-1), PI-86023 (- LOX-2), TOHOKU no 74 (-LOX-3)}, using the commercial cultivar IAC-8, resulting in the seeds IAC 97-3503, IAC 97-3512, IAC 97-3545 and IAC 97-3808, which have been furnished by the Instituto Agronômico de Campinas (IAC). The qualitative and quantitative analysis of the samples were done beyond: 1)Electrophoresis in gel of poliacrilamida and SDS, to discriminate the existing bands; 2) color test and; 3) determination of the enzymatic activity using espectofotometric in the presence of: 3.1) specific subtracts and; 3.2) connected reaction of ß-carotene bleaching. It has been observed that beyond electrophoresis in gel each band corresponds to each isoenzyme. The oxidation reaction of LOX in the ß-carotene (LOX-3) and methyl blue (LOX-2 and LOX-1) was sensible for the detection of LOX-1 and LOX-3. The method for determination of enzymatic activities with utilization of substrates (linoleic acid for LOX-1 and LOX-3, and methyl-linoleate acid for LOX-2) it was sensible for detection of LOX-1 and LOX-3. Beyond the reaction of the co-oxidation of ß-carotene by LOX-2 and LOX-3, it was possible to determinate all the isoenzymes, adding the final result which was obtained first beyond electrophoresis in gel of poliacrylamide, and it has been saw that beyond the crossing and backcrosses been made by the IAC, the seed IAC 97-3503 haven¿t shown any activity of LOX-1, to he step of it hasn¿t been observed any significant reduction (p<0,05) in the others seeds that had been studied. A significant reduction had been shown (p<0,05) in LOX-2 in the seeds IAC 97-3512 and IAC 97- 3545 when they were compared to the standard IAC 8-2. To LOX-3 it had been observed a significant reduction (p<0,05) in the seed IAC 97-3503, and no reduction had taken place in the others cultures three seeds / Mestrado / Mestre em Alimentos e Nutrição

Autoxidation, a radical chain reaction, is largely responsible for the degradation of most man-made and biological materials. These include chemical products such as lubricants, plastics and rubber; as well as biological molecules and membranes within our bodies. The development of means to hinder this process has been a major focus of the petroleum, chemical, pharmaceutical and biotechnology industry over the past century. The two most common strategies to emerge from these efforts have been the use of compounds that either prevent the initiation of autoxidation or trap the propagating radicals, so-called radical-trapping antioxidants (RTAs). Herein, we describe our efforts towards the design and development of extremely potent heterocyclic diarylamine RTAs, and their activity in a variety of applications ranging from isotropic organic solution to mammalian cells. We have elucidated the important structural motifs and mechanistic considerations necessary for the development of next-generation arylamine RTAs. Some of the substituted heterocyclic diarylamines analogs we disclose are among the best inhibitors of high temperature autoxidations described to date. Alongside, we developed novel analytical tools to facilitate the studies and acquisition of results for characterizing RTA activity in organic solutions and lipid bilayers. These fluorescent probes are highly relevant and allow for the determination of hydroperoxide and acid concentrations rapidly, as well as screen (or counter-screen) RTAs in liposomal membranes. Our methodologies address numerous drawbacks from frequently used ‘plug-and-play’ assays and we anticipate they will fill a current unmet need in both industrial and academic laboratories worldwide. Moreover, the recent characterization of ferroptosis – a novel regulated necrotic-like cell-death pathway associated with the accumulation of lipid hydroperoxides – has paved a way forward for studying oxidation induced damage in a biological context. Utilizing our expertise in lipid peroxidation and inhibition, we elucidated the prominent role of autoxidation in the execution of ferroptotic cell death. Alongside, our analytical tools and RTAs have also enabled the identification and characterization of novel ferroptosis inhibitors. Furthermore, this has prompted the development of a correlation to predict anti-ferroptosis activity of small-molecules using simple spectrophotometric assays.

Indiana University-Purdue University Indianapolis (IUPUI) / Type 1 and Type 2 diabetes (T1D/T2D) share a common etiology that involves an increase in oxidative stress that leads to dysfunction and subsequent β cell death. Lipoxygenases are enzymes that catalyze the oxygenation of polyunsaturated fatty acids to form lipid metabolites involved in a variety of biological functions including cellular oxidative stress response. On the other hand, Interleukin 6 (IL-6) signaling has been demonstrated to be protective in islets. In this study, we explored the effect of lipoxygenase enzymes 12-Lipoxygenase, 12/15 Lipoxygenase and IL-6 on β cell function and survival in mice using both STZ and high-fat diet (HFD) models of diabetes. Alox12-/- mice showed greater impairment in glucose tolerance following STZ and HFD compared to wild-type mice (WT), whereas Alox15-/- were protected against dysglycemia. These findings were accompanied by evidence of islet oxidative stress in Alox12-/- mice and reduced oxidative stress in Alox15-/- mice, consistent with alterations in the expression of antioxidant response enzymes in islets from these mice. Additionally, islets from Alox12-/- mice showed a compensatory increase in Alox15 gene expression and treatment of these mice with the 12/15-lipoxygenase inhibitor ML-351 rescued the dysglycemic phenotype. IL-6 was able to significantly attenuate the generation of reactive oxygen species by proinflammatory cytokines in human pancreatic islets. Furthermore, we find that IL-6 regulates the master antioxidant response protein NRF2. Collectively these results show that loss of Alox12 activates a compensatory increase in Alox15 that sensitizes β cells to oxidative stress and signaling by IL-6 is required for maximal antioxidant response under conditions of increased ROS formation, such as obesity.

Indiana University-Purdue University Indianapolis (IUPUI) / Diabetes is a morbid metabolic disorder that affects almost 500 million people worldwide. Although multiple factors contribute to diabetes pathogenesis, pancreatic islet inflammation and dysfunction are shared characteristics of its major forms. 12- lipoxygenase (12-LOX), an enzyme involved in lipid metabolism, has been implicated in islet inflammation. 12-LOX generates reactive oxygen species (ROS) that activate inflammation and serve as major contributors to islet dysfunction. Importantly, since ROS are transient moieties, they are challenging to study in vivo. Hence, establishing better animal models of ROS-mediated stress is critical to facilitate the discovery and preclinical testing of novel diabetes therapeutics. Here, I have adapted a zebrafish model of conditional β-cell injury, which is regulated by the administration of the prodrug metronidazole (MTZ), to study responses to ROS in vivo. I demonstrate that with MTZ treatment, ROS are generated within β-cells and subsequently exhibit recruitment of macrophages into the islet and induction of β-cell death. I utilized this model to uncover roles for macrophages and 12-LOX during islet injury. Excessive macrophage infiltration exacerbates islet inflammation and dysfunction. Interestingly, on the depletion of macrophages in zebrafish, I observed that β-cells recovered normal function upon cessation of prodrug treatment. This suggests that infiltrating macrophages promote maladaptive inflammation and premature removal of damaged β-cells. Thus, limiting the macrophage infiltration may be a therapeutic approach to restoring β-cell function. Based on the established roles of 12-LOX in other contexts, I hypothesized that its inhibition would prevent the localized infiltration of proinflammatory macrophages. To test this, I used both zebrafish and mouse models and observed a significant reduction in macrophage migration upon loss of 12- LOX activity. Furthermore, I found that expression of CXCR3, a crucial receptor regulating migration, was significantly reduced in 12-LOX loss-of-function macrophages. These data suggest a role for 12-LOX in macrophages, which is conserved across species. Collectively, my study reveals novel roles for 12-LOX in macrophage function and provides testable therapeutic targets for the resolution of inflammation-induced damage in the pancreatic islets. / 2020-11-19

No description available.

The goal of this research is to determine the effects of added soybean lipoxygenase (LOX) on bread dough rheological properties and physical properties of bread loaves compared to controls, and to determine sensory attributes of bread loaves using quantitative descriptive analysis (QDA). Protein fractions were obtained through the use of isoelectric precipitation. The pH 4.8 precipitate was found to yield the greatest LOX activity when compared with other fractions (p<0.05). The addition of pH 4.8 precipitate improved rheological properties of bread dough, examined in a farinograph, when compared to the all-purpose control (p<0.05). Addition of soy flour also increased the gluten strength of all-purpose flour (p<0.05). The addition of pH 4.8 precipitate to all-purpose flour did not improve bread loaf volume or texture. Sensory panelists described pH 4.8 supplemented bread as having firmer crumb when compared with controls (p<0.05). There were slight color differences among the loaves. The crust and crumb of bread flour loaves was lighter in color than any other sample. It was concluded that the addition of pH 4.8 precipitate to all-purpose flour greatly improved the rheological properties when compared with all-purpose flour alone. / Master of Science

La RH est une réaction de défense. L’interaction entre G.hirsutum et Xcm repose sur le concept gène-à-gène. L’infection du cultivar Réba B50 possédant les gènes R B2B3 par Xcm18 conduit à une RH associée à une activité LOX, responsable de la peroxydation des lipides, et à la transcription du GhLOX1. Premièrement, 6 génotypes de G.hirsutum contenant divers gènes R ont été retenus pour analyser la variabilité de la réponse LOX suite à l’infection par Xcm1, 18 ou 20. Notre étude a porté sur plusieurs critères, le phénotype, la perte en eau, l’activité LOX et la transcription du GhLOX1. Les résultats montrent une variabilité du phénotype RH en fonction des sources de résistances. Pour chaque type d’interaction incompatible, l’activité LOX et la transcription du GhLOX1 révèlent une augmentation significative corrélée à l’apparition des symptômes RH et à la diminution de la teneur en eau. La réponse LOX est conservée lors de la RH, quelle que soit la race de Xcm ou le génotype. Le GhLOX1 considère comme un marqueur moléculaire de la résistance spécifique du cotonnier à Xcm. Deuxièmement, le rôle du GhLOX1dans la mise en place de la RH en analysant sa fonction potentielle par surexpression. Des cotylédons ont été transformés avec la séquence codante GhLOX1 fusionnée au CaMV35S. Ces cotylédons transformés ont révélé (i) une activité LOX significativement supérieure à celle des cotylédons témoins montrant que le GhLOX1 code pour une protéine active et (ii) un phénotype sans modifications apparentes par rapport à celui des cotylédons non transformées, sauf dans certains contextes d’interactions cotonnier/Xcm où la surexpression de ce gène induit l’apparition de symptômes de type RH. L’effet de l’agro-infiltration sur l’expression de certains gènes pendant la transformation a révélé l’induction précoce et non spécifique de l’expression de gènes de défense. Ces travaux constituent une première étape dans l’analyse fonctionnelle du GhLOX1 dans la résistance spécifique du cotonnier à Xcm / The HR is a defense strategy. The interaction between G.hirsutum and Xcm is governed by the gene-for-gene concept. The infection of the cultivar Reba B50 that contains B2B3 R genes by race Xcm18 leads to a HR associated with a LOX activity response involved in peroxidation of lipids and with transcription of GhLOX1. First, 6 genotypes of G. hirsutum containing various R genes were tested to analyze the variability of the LOX response following the infection by Xcm1, 18 or 20. Several criteria were investigated including the phenotype, the water loss, the LOX activity and GhLOX1 transcription. The results showed variation in HR phenotype according to the tested R genes. For each type of the incompatible interaction, LOX activity and transcription of GhLOX1 were always significantly increased paralleled the apparition of the HR symptoms and the decrease in the water content. LOX response (enzymatic activity and GhLOX1 transcription) is associated with HR whatever the genotype of both Xcm races and cotton plant. Thus, the GhLOX1 consider as a molecular marker of the cotton specific resistance to Xcm. Second, the role of the GhLOX1 gene in the execution of the cotton HR to Xcm by analyzing its possible function by over-expression, the cotyledons were transformed with the GhLOX1 coding sequence fused to the CaMV35S. These transformed cotyledons revealed (i) a LOX activity significantly higher than that detected in the control, showing that the GhLOX1 encodes for an active protein and (ii) that the phenotype of these cotyledons was indistinguishable as compared to the non transformed cotyledons, except when the HR symptoms were induced in some GhLOX1-over-expressed cotyledons. The effect of agro-infiltration on expression of some plant genes during the transformation revealed early and nonspecific induction of the expression of defense genes. This work constitutes a preliminary investigation for the functional analysis of the GhLOX1 in order to assess its role in the cotton specific resistance to Xcm

No description available.

Um eine Verbindung zwischen den bereits bekannten in vitro-Effekten und der bislang weitgehend ungeklärten in vivo-Situation zu knüpfen, wurden der intestinale Metabo-lismus sowie die Lipoxygenase-hemmenden Eigenschaften von ausgewählten sekun-dären Pflanzeninhaltsstoffen mit verschiedenen Modellsystemen untersucht. Folgende kamen zur Anwendung: intestinaler Metabolismus Lipoxygenase-hemmende Eigenschaften - menschlicher Speichel - Soja Lipoxygenase-1 - künstlicher Magensaft - 5-Lipoxygenase aus humanen neu- - Ileostomabeutelinhalt trophilen Granulozyten - Kolostomabeutelinhalt Die ex vivo-Modellsysteme (Ileo- und Kolostomabeutelinhalte, 5-Lipoxygenase aus menschlichen neutrophilen Granulozyten) wurden speziell auf metabolische Kompe-tenz beziehungsweise Zellvitalität überprüft. Die verwendeten Darminhalte wiesen ein breites Spektrum an Enzymaktivitäten und angemessene Zahlen anaerober kolonien-bildender Einheiten auf. Nach Isolierung der neutrophilen Granulozyten aus periphe-rem Humanblut erwiesen sich sowohl Zellvitalität (> 90% lebende Zellen) als auch Zellkonzentration (> 5000 Zellen/ µl) für unsere Studien als geeignet. Mit diesen sorg-fältig geprüften Modellsystemen wurden folgende Anwendungen untersucht: I. Einfluss des Zuckerrests, der Aglyconstruktur und der Mikroflorakonzentration auf die Hydrolyse von Phenolglycosiden im menschlichen Dünndarm II. Inkubation der gegen ileale Hydrolyse/Abbau resistenten Verbindungen mit Kolostomabeutelinhalten III. Einfluss des Zuckerrests und der Aglyconstruktur auf die Hydrolyse von Hei-delbeeranthocyanen im menschlichen Dünn- und Dickdarm IV. Metabolismus von D-Galacturonsäure und amidiertem Pektin V. Flavonoide und deren intestinale Metabolite als Soja Lipoxygenase-1-Inhibi-toren VI. Anthocyane als Lipoxygenase-Inhibitoren: Studien mit Soja Lipoxygenase-1 sowie 5-Lipoxygenase aus menschlichen neutrophilen Granulozyten Hierzu wurden Quercetin- und p-Nitrophenolglycoside (hier: 3-O-&#946;-D-Glucoside, 3-O-&#946;-D-Galactoside, 3-O-&#945;-L-Arabinoside, 3-O-&#946;-D-Xyloside und 3-O-&#945;-L-Rhamno-side), anthocyanreicher Heidelbeerextrakt, D-Galacturonsäure und amidiertes Pektin unter anaeroben &#61506;edingungen bei 37°C für 24 beziehungsweise 10 h mit Ileostoma-beutelinhalten von gesunden Probanden inkubiert. Zusätzlich wurden Quercetin, Quer-cetin 3-O-&#945;-L-rhamnopyranosid, Chlorogensäure, Procyanidin B2, (-)-Epicatechin, Phloretin, D-Galacturonsäure und amidiertes Pektin unter anaeroben Bedingungen bei 37°C für 24 h mit Kolostomabeutelinhalten von gesunden Probanden inkubiert. Die Substrate und Metabolite wurden mittels Hochdruckflüssigchromatographie-Dioden-array-Detektion (HPLC-DAD) und HPLC-Elektrospray-Ionisierung-Tandemmassen-spektrometrie (HPLC-ESI-MS/MS) identifiziert. Die Gehalte von D-Galacturonsäure und amidierten Pektin wurden nach Carbazolreaktion photometrisch bestimmt. Metha-nol wurde via Headspace Solid-phase Microextraction Gaschromatographie/Massen-spektrometrie (HS-SPME-GC/MS) gemessen; die Bestimmung kurzkettiger Fettsäuren (SCFA) erfolgte mittels GC-Flammenionisations-Detektion (GC-FID). Die Enzym-versuche wurden spektrophotometrisch ausgewertet, wobei die Bildung des Hydroper-oxidprodukts bei 234 nm beziehungsweise 236 nm verfolgt wurde. / To develop a link between the already known in vitro effects of various secondary plant constituents and the still unclear in vivo situation, both the intestinal metabolism and the lipoxygenase-inhibitory properties of selected secondary plant constituents were studied with various model systems. The following were applied: intestinal metabolism lipoxygenase-inhibitory properties - human saliva - soybean lipoxygenase-1 - simulated gastric juice - human neutrophil granulocyte - human ileostomy fluid 5-lipoxygenase - human colostomy fluid The ex vivo model systems (i.e. ileostomy and colostomy fluids, human neutrophil granulocyte 5-lipoxygenase) were particularly checked for metabolic competence and cell viability, respectively. The screened intestinal fluids showed a broad range of enzymatic activities and proper counts of anaerobic colony forming units. After isola-tion of neutrophil granulocytes from human peripheral blood, the cell vitality (> 90% viable cells) and cell concentration (> 5000 cells/ µl) were adequate for our studies. With these carefully proved model systems, the following applications were perfor-med: I. Influence of sugar moiety, aglycon structure and microflora concentration on the human ileal hydrolysis of phenol glycosides II. Incubation of compounds resistant to ileal hydrolysis/degradation with human colostomy fluids III. Influence of sugar moiety and aglycon structure on the hydrolysis of bilberry anthocyanins in the small and large intestine of humans IV. The metabolism of D-galacturonic acid and amidated pectin V. Flavonoids and corresponding intestinal metabolites as soybean lipoxygenase-1 inhibitors VI. Anthocyanins as lipoxygenase inhibitors: studies with both soybean lipoxyge-nase-1 and human neutrophil granulocyte 5-lipoxygenase Thus quercetin and p-nitrophenol glycosides (i.e. 3-O-&#946;-D-glucosides, 3-O-&#946;-D-galac-tosides, 3-O-&#945;-L-arabinosides, 3-O-&#946;-D-xylosides and 3-O-&#945;-L-rhamnosides), antho-cyanin-rich bilberry extract, D-galacturonic acid and amidated pectin were incubated under anaerobic conditions at 37°C for 24 and 10 h, respectively, with ileostomy fluids from healthy volunteers. In addition, quercetin, quercetin 3-O-&#945;-L-rhamnoside, chlo-rogenic acid, procyanidin B2, (-)-epicatechin, phloretin, D-galacturonic acid and ami-dated pectin were incubated under anaerobic conditions at 37°C for 24 h with colo-stomy fluids from healthy volunteers. The substrates and metabolites were identified by high performance liquid chromatography-diode array detection (HPLC-DAD) and HPLC-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS). The contents of D-Galacturonic acid and amidated pectin were determined photometrically after carbazole reaction. Methanol was measured via headspace solid-phase microex-traction gas chromatography/mass spectrometry (HS-SPME-GC/MS) and short chain fatty acids (SCFA) were determined by GC-flame ionisation detection (GC-FID). The enzyme assays were analyzed spectrophotometrically, monitoring the appearance of hydroperoxide products at 234 nm and 236 nm, respectively.

Catechine gehören als Flavan-3-ole zur Gruppe der Polyphenole. Aufgrund deren vielfältiger positiver Effekte auf den menschlichen Organismus nehmen sie in der Ernährungsforschung einen hohen Stellenwert ein. Dabei hat man bei den Flavan-3-olen meist nur die in der Natur vorherrschenden Isomere (+)-Catechin und (-)-Epicatechin untersucht, doch auch (-)-Catechin und (+)-Epicatechin sind Naturstoffe. Letztere findet man z.B. in Guarana oder in verarbeiteten Lebensmitteln, wie z.B. Kakao- und Kakaoerzeugnissen. Sie entstehen durch Epimerisierung unter den technologischen Bedingungen beim Rösten der Kakaobohnen und der Alkalisierung der Kakaomasse. Bei der Kakao-Verarbeitung werden ferner auch Catechin-C-Glykoside gebildet. Im ersten Teil dieser Arbeit wurden Stabilitätsstudien mit (+)-Catechin bei unterschiedlichen pH-Werten und Temperaturen durchgeführt. Der zweite Teil dieser Arbeit umfasst Untersuchungen von Catechin-Isomeren und zwei Catechin-C-Glykosiden auf ihren Einfluß auf die Lipoxygenase (LOX)- und Xanthinoxidase (XOD)-Aktivität. Für die Catechin-C-Glykosidbildung ist von uns eine neue Vorstellung zu deren Entstehungsmechanismus im Laufe der Lebensmittelverarbeitung entwickelt worden. Abschließend wurden anhand von Modelling-Studien die Effekte auf die Enzymsysteme erklärt. / As flavan-3-ols, catechins belong to the group of polyphenols. Due to their manifold positive effects on the human organism, catechins are of important significance in food research. Although only the two most abundant isomers in nature, (+)-catechin and (-)-epicatechin, have been studied in most cases; however, (-)-catechin and (+)-epi-catechin occur in nature as well. The latter are found i.e. in guarana or in processed food, as cacao and cacao products as the result of epimerization due to technological processing, i.e. while roasting the cocoa beans and alkalisation of the cacao mass. Catechin-C-glycosides are also formed during cacao processing. In the first part of this thesis stability studies with (+)-catechin at different pH values and temperatures were carried out. The second part of this work comprises analysis of catechin isomers and two catechin-C-glycosides on their influence on lipoxygenase (LOX)- and xanthinoxidase (XOD)-activity. For the building mechanism of catechin-C-glycosides during food processing a new hypothesis was developed. Finally the effects on enzyme systems were explained by means of modelling studies.