No description available.

This study is concerned with the metabolism of L-asparagine in Lactobacillus plantarum (ATCC 8014). Theprimary area of investigation is the preliminary characterization of a previously unreported L-asparaginase enzyme in L. plantarum. This L-asparaginase was determined to be an inducible enzyme with variations in its activity level according to the L-asparagine level in the growth medium. L-Glutaminase could not be induced in this organism by L-glutamine, nor would L-glutamine induce the asparaginase activity. These and other studies with amino acid analogs demonstrated the high specificity of both induction and enzymic activity of the asparaginase. Various physical properties of the enzyme were studied. The enzyme was found to be inhibited by adenosine triphosphate (ATP). This inhibition appears to be cooperative in nature and of the type exhibited by allosteric enzymes. These studies should be confirmed on a highly purified enzyme as these preliminary experiments were performed using a crude cell-free extract.

No description available.

No description available.

That Lactobacillus arabinosus 17-5, ATCC 8014, can supply its own requirement for the amino acid, lysine, is demonstrated by the fact that the organism is capable of growth in media devoid of lysine. Since the final biosynthetic step in lysine formation in all bacteria studied to date involves the decarboxylation of meso-dlaminopimelic acid (DAP) to produce lysine, it was of interest to determine whether an enzyme catalyzing such a reaction (DAP decarboxylase) is present in L. arabinosus.

The diploma thesis deals with the Influence of the Enzyme L-asparagine and the Inorganic salts (NaCl, CaCl2, NaHCO3 and NH4HCO3) on the elimination of the acrylamide in food-stuffs and a simulated model cereal matrix. The acrylamide belongs to the probable carcinogenic compounds which is incipient in the course of thermal processing of food, which are rich in the reducing sugars and amino acids as L-asparagine. Because of L-asparagine is the natural component of cereals and simultaneously is dominant antecedent incipient acrylamide, the way of the elimination by enzyme L-asparaginase (or the combination of L-asparaginase and salt) leads to the reduced level of acrylamide in a final product. The L- asparagine and salts were used on food-stuffs and a simulated model cereal matrix. It was found that individual used substances (except for NH4HCO3) cause the reduction of acrylamide production even about 90 % without change in the sensory properties of final product.

Chan Hiu-ki. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 97-112). / Abstracts in English and Chinese. / Thesis Committee --- p.i / 摘要 --- p.ii / Abstract --- p.iii / Acknowledgements --- p.v / Abbreviations --- p.vi / Table of Contents --- p.vii / List of figures --- p.xi / List of tables --- p.xiii / Chapter Chapter 1 --- Literature Review --- p.1 / Chapter 1.1 --- Nitrogen assimilation in plants --- p.1 / Chapter 1.2 --- Importance of asparagine in plants --- p.5 / Chapter 1.3 --- Enzymatic reaction of asparagine synthetase (AS) --- p.8 / Chapter 1.4 --- Asparagine synthetase of non-plant organisms --- p.10 / Chapter 1.5 --- Biochemistry background of plant asparagine synthetases --- p.12 / Chapter 1.6 --- Molecular studies of asparagine synthetase genes in plants --- p.15 / Chapter 1.7 --- Arabidopsis thaliana as a model plant --- p.24 / Chapter 1.8 --- ASN studies in Arabidopsis thaliana --- p.24 / Chapter 1.9 --- Hypothesis --- p.27 / Chapter Chapter 2 --- Materials and Methods --- p.29 / Chapter 2.1 --- Chemicals --- p.29 / Chapter 2.2 --- Plant materials and growth conditions --- p.29 / Chapter 2.2.1 --- Surface sterilization of Arabidopsis seeds --- p.29 / Chapter 2.2.2 --- "Growth conditions of Arabidopsis seeds for total RNA extraction, enzyme assay, chlorophyll content measurement and dry weight measurement" --- p.30 / Chapter 2.3 --- Agrobacterium mediated transformation via vacuum infiltration method --- p.30 / Chapter 2.3.1 --- Principles --- p.30 / Chapter 2.3.2 --- Plant materials and bacterial strains of Agrobacterium mediated transformation --- p.31 / Chapter 2.3.2.1 --- Plant materials --- p.31 / Chapter 2.3.2.2 --- Gene constructs --- p.31 / Chapter 2.3.2.2 --- Bacterial strains --- p.32 / Chapter 2.3.3 --- Agrobacterium mediated transformation via vacuum infilitration --- p.32 / Chapter 2.4 --- Screening of transformants --- p.33 / Chapter 2.5 --- DNA and RNA manipulation --- p.34 / Chapter 2.5.1 --- DNA extraction and quantitation --- p.34 / Chapter 2.5.2 --- PCR amplification and detection of transgenes --- p.36 / Chapter 2.5.2.1 --- PCR amplification and detection of transgenes --- p.36 / Chapter 2.5.2.2 --- Primer sequence --- p.37 / Chapter 2.6 --- RNA analysis of transormants --- p.38 / Chapter 2.6.1 --- General introduction --- p.38 / Chapter 2.6.2 --- RNA extraction --- p.39 / Chapter 2.6.3 --- Making single-strand DIG PCR probes --- p.40 / Chapter 2.6.4 --- Quantitation of single-strand DIG-labeled probes --- p.42 / Chapter 2.7 --- Northern blot analysis --- p.42 / Chapter 2.7.1 --- Detection --- p.43 / Chapter 2.7.2 --- Film development --- p.43 / Chapter 2.8 --- "Amino acid, protein, dry weight and total nitrogen analysis" --- p.43 / Chapter 2.8.1 --- Extraction of free amino acids --- p.43 / Chapter 2.8.2 --- Protein assay --- p.44 / Chapter 2.8.3 --- Determination of nitrogen and carbon content in seeds --- p.45 / Chapter 2.8.4 --- Dry weight measurement --- p.45 / Chapter 2.8.5 --- Seed storage protein analyses --- p.45 / Chapter 2.8.6 --- Detection of chlorophyll content --- p.46 / Chapter 2.9 --- Asparagine synthetase activity analysis --- p.46 / Chapter 2.9.1 --- Crude extracts preparation --- p.46 / Chapter 2.9.2 --- AS enzyme assay --- p.47 / Chapter 2.9.3 --- Asparagine content measurement --- p.47 / Chapter 2.10 --- In situ hybridization --- p.48 / Chapter 2.10.1 --- Making cRNA probe --- p.48 / Chapter 2.10.2 --- In situ hybridization --- p.48 / Chapter Chapter 3 --- Results --- p.50 / Chapter 3.1 --- Construction of ASN1 overexpressing lines --- p.50 / Chapter 3.2 --- Changes in nitrogen status during vegetative growth of ASN1 overexpressing lines --- p.53 / Chapter 3.3 --- Changes in nitrogen status during seed development of ASN1 overexpressing lines --- p.55 / Chapter Chapter 4 --- Discussion --- p.76 / Chapter Chapter 5 --- Conclusion --- p.85 / Chapter Chapter 6 --- Perspective --- p.86 / Appendix --- p.87 / References --- p.97

L'acrylamide, connu comme étant une molécule cancérigène, apparait lors de traitement thermique à haute température (>120°C) d'aliments riches en asparagine et en sucre. La friture profonde génère ce composé à des teneurs proche de 0,44 ppm pour les chips de plantain. Or les aliments à base de plantain sont largement consommés dans les pays du sud. Ces travaux de recherche ont pour objectif de mieux comprendre l'accumulation de l'acrylamide lors de l'élaboration de produits frits à base de plantain. Pour y parvenir la teneur en précurseurs (asparagine) a d'abord été obtenue dans différentes variétés de bananes, mais aussi durant le mûrissage d'une variété de plantain d'exportation (Harton). Ces résultats ont permis d'identifier l'asparagine comme étant limitant pour la formation d'acrylamide dans le plantain. Ensuite, une étude cinétique du couplage entre la température et l'activité en eau a été entreprise en système fermé. Le domaine d'étude consistait en 4 températures de traitement (140, 160, 180 et 200°C) et 3 activités en eau (0,43 ; 0,9 ; 0,97). La cinétique de formation et d'élimination de l'acrylamide a été traduite par la somme de 2 cinétiques d'ordre 1. Les paramètres cinétiques ont été identifiés et montrent que la température est le paramètre qui influence le plus la cinétique de l'acrylamide. Le modèle cinétique a dans une autre étape été couplé à un modèle traduisant les transferts d'énergie et de vapeur durant la friture. Le modèle a bien simulé les teneurs en eau et en acrylamide de deux produits frits à base de plantain « tajadas » (produit épais) et « tostones » (produit mince). Les coulages entre transfert et réaction sont discutés en vue d'imaginer des stratégies de réduction de l'acrylamide. Il a été démontré que la formation de l'acrylamide se fait presque exclusivement dans la zone hygroscopique périphérique (croûte). De ce fait, la conduite de la friture en températures variables est recommandée et permet de réduire d'au moins 50% la teneur en acrylamide. La sélection variétale et l'état de maturité du plantain sont les moyens en amont les plus souples pour contrôler la teneur en acrylamide dans le produit final. Des prétraitements par immersion se sont avérés efficaces induisant une réduction significative de l'acrylamide. En revanche, la formulation de molécules antioxydantes ne semble pas avoir d'effet réducteur. / Acrylamide, a molecule known as a carcinogen, appears during heat treatment of asparagine and sugars rich foods at high temperature (> 120 ° C). Deep frying produces this compound at levels close to 0.44 ppm for plantain chips, these foods being widely consumed in developing countries. The aim of the present work is to better understand the accumulation of acrylamide during the process of plantain-based products. In this context, the level of precursors (asparagine) was obtained firstly in different varieties of bananas and also during ripening of an export plantain variety (Harton). These results allowed identifying asparagine as a limiting factor of acrylamide formation in plantain. Afterwards, a kinetic study of the coupling between temperature and water activity was undertaken in a closed system. The field of study consisted of four temperatures of treatment (140, 160, 180 and 200 ° C) and three water activities (0.43, 0.9, 0.97). The kin etics of formation and elimination of acrylamide was translated by the sum of 2 order 1 kinetics. The kinetic parameters were identified and showed that temperature is the parameter that influences the most acrylamide kinetic. The kinetic model, in a further step, was coupled to a model describing energy and steam transfers during frying. The model simulated well water and acrylamide content in two plantain-based fried products: "Tajada" (produced thick) and "tostones" (thin product). The coupling between transfers and reaction were discussed in order to identify strategies to reduce acrylamide. It was demonstrated that acrylamide formation occurs almost exclusively in the hygroscopic and peripheral area (crust). Thus, conducting frying process at varying temperatures is recommended and can reduce by at least 50% the acrylamide content. The varietal selection and the ripeness degree of plantain are more flexible ways to control upstream the levels of acrylamide in the final product. Immersion pretreatments were also effective to reduce significantly acrylamide. However, the formulation of antioxidant molecules did not appear to have reduction effect.