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ANWENDUNG VON IMMOBILISIERTEN LIPASEN ZUR UMESTERUNG VON SPEISEFETTEN
No full textThe application of an immobilized lipase for the
interesterification of lipids in a continuous solvent-free system has
been studied. Important engineering parameters which are necessary for
the design of a bioreactor e.g. a fixed bed reactor has been examined.
The pressure drop across a fixed bed (Hp= 0,7 m; T = 60 °%;
Ug = 7° 10 74 m/s) was 0,5 bar. The flow of the substrate through the
biocatalyst bed can be described by a linear equation. The influence
of internal and external mass transfer limitations on the conversion
of the reaction has been tested in stirred tank reactors and fixed bed
reactors. The reaction rate is influenced by internal diffusion
effects. Film diffusion limitations can be neglected for flow rates
over 8,0 + 10 "° ms
LACTATE DEHYDROGENASE : EFFECT OF AMINO ACID CHANGES ON PROPERTIES
No full textMany changes have been made by protein engineering in lactate dehydrogenase from
B.stearothermophilus. The role of groups involved in susbtrate and coenzyme
binding, catalysis and effector molecule binding has been deduced and variants with
improved thermal stability developed. The native substrate catalysis patern of
lactate dehydrogenase has been modified by many orders of magnitude, to convert
this protein into essentially a highly active malate dehydrogenase. Work is
Currently on-going to modify this further and to convert malate dehydrogenase,
Similarly by protein engineering, into a functional lactate dehydrogenase
KONZEPT UND ENTWICKLUNG DER ENZYMATISCHEN LEBENSMITTELKONSERVIERUNG
No full textDas Interesse der Verbraucher bezüglich Ernährung richtet sich neben der Forderung
nach Geschmack und Unbedenklichkeit zunehmend nach einem Höchstmaß an "convenience",
nach der Anpassung an ernährungsphysiologische Notwendigkeiten (Kalorienreduktion)
und nach einer möglichen Vermeidung von naturfremden Hilfsstoffen bei der Lebensmittelherstellung. Erkenntnisse der Biotechnologie können zur Bereitstellung "natürlicher"
Lebnsmittelzusatzstoffe genutzt werden, wobei auch Konservierungsstoffe zu nennen
sind. Es wird ein Konzept zur Lebensmittelkonservierung mittels Enzymen vorgestellt,
die als Alternative zu physikalischen Verfahren der Haltbarmachung bzw. zu traditionellen chemischen Konservierungsstoffen in Betracht gezogen werden können. Enzyme
mit bakterienlysierender Wirkung sind in der Natur weit verbreitet; aus Hühnereiern
wird Lysozym im technischen Maßstab gewonnen und für den Pharma- und Ernährungssektor verkauft.
Daneben kann Lysozym auch fermentativ hergestellt werden. Anhand dieses fermentativen Lysozyms wird der Entwicklungsweg vom Primärscreening nach bakterienlysierenden
Enzymen bis zur technischen Fermentation beschrieben. Ensprechend muß die Entwicklung von schimmelpilz- und hefelysierenden Enzymen betrieben werden. Die Wirkspektren und die minimalen Hemmstoffkonzentrationen dieser Enzyme sind in entsprechenden
in-vitro Untersuchungen sowie Anwendungsversuchen zu erfassen
ENZYMATISCHE HYDROLYSE VON INULIN AUS TOPINAMBUR ZUR HERSTELLUNG EINES FRUCTOSEHALTIGEN SAFTES
No full textDer Konsum von Gemüsesäften in den europäischen Ländern macht nur einen
geringen Bruchteil, etwa 0,5 - 3 % des Anteils der Fruchtsäfte und Fruchtsaftgetränke aus. Trotz dieses niedrigen Verbrauchs von Gemüsesäften verdienen diese ausgesprochen kalorienarmen Säfte erhöhte Beachtung, vor
allem, weil sie appetitanregend und verdauungsregulierend wirken und dazu als Vitamin- und Mineralstoffspender von größter Bedeutung sind./1/
Der nachwachsende Rohstoff Topinambur ( Helianthus tuberosus L. ), der
aus den nördlichen Regionen Nordamerikas stammt, wird seit Anfang des
17. Jahrhunderts in Europa kultiviert. Unter dem neuen Aspekt der Bioenergieproduktion kommt Topinambur wegen ihres hohen Energiepotentials
vermehrte Bedeutung zu. Zu nennen ist in diesem Zusammenhang der medizinisch und ernährungsbedingt begründete Einsatz von D-Fructose als Süssungsmittel in der Lebensmittel- und Getränkeindustrie./2,3,4,8/Die Verwendung von Topinamburprodukten im diätetischen Bereich ist ebenfalls zu
erwähnen./9/Außerdem stellt Topinambur als Substrat für die Produktion
von hochfructosehaltigen Sirupen eine natürlich vorkommende D-FructanQuelle dar./5
DEVELOPMENT OF AN AGAR-MEDIUM (ESCULIN CELLOBIOSE AGAR) FOR THE DETECTION AND ENUMERATION OF LACTOBACILLUS ACIDOPHILUS
No full textAn agar-medium (Esculin cellobiose agar) is presented which enables the detection and
quantitative determination of Lactobacillus acidophilus in dairy products, especially
in fermented milk products. For this purpose the ability of L.acidophilus to grow at
40 °C, to ferment cellobiose, and to hydrolyse esculin to esculetine is used. Esculetine forms in combination with Fe (III) ions and olive-green to black complex. For a
further differentiation the addition of chlorophenolred was useful. In total 60
strains of lactobacilli, streptococci, and bifidobacteria from 22 species were
examined regarding their growth on EC-agar. Only L.acidophilus, L.casei-rhamnosus and
L.plantarum could not be differentiated distinctly
MODIFICATION OF MILK-CLOTTING ASPARTIC PROTEASES, CHYMOSIN AND MUCOR RENNIN
No full textArtificial mutagenesis of milk-clotting aspartic proteases,
chymosin and a fungal aspartic protease from Mucor pusillus (MPR), was
carried out by recombinant DNA techniques. The native and the
modified chymosins were prepared by using the expression system of
Escherichia coli and their activities were measured with aciddenatured
haemoglobin and synthetic peptides. A marked change of
substrate specificity with a change of Km or kcat was observed with
the mutation of 17077) on’ the flap structure to Phe. Involvement of
Lys(221) in determining the pH-activity profile was also suggested.
Correctly processed but highly glycosylated MPR was secreted from
yeast cells carrying the fungal gene. The decreased milk-clotting
activity of the yeast MPR was improved by treatment with
endoglycosidase H. Exchange of the Tyr residue on the flap and
Trp(45) suggested that the hydrogen bonding between these residues is
required for correct arrangement of the S1 subsite.
X-ray crystallographic analysis of several aspartic proteases
has revealed that 3-dimensional structures of these enzymes are very
similar to each other (1). The molecules are bilobal, composing of
two topologically similar domains rich in 6 -sheet structures. Their
junction forms an extended substrate binding cleft and the two
essential aspartyl residues reside at the bottom of the Cleft . A
flexible flap region is located at the entrance of the cleft and a
tyrosine residue on the flap as well as several hydrophobic residues
in the adjacent region are involved to form the Sl subsite for
substrate binding. In spite of these high similarity in tertiary
structures, marked diversity of the catalytic activity and substrate
specificity in these enzymes suggest that different sets of amino acid
residues may be involved in their catalytic functions.
Calf chymosin and a fungal aspartic protease produced by Mucor
pusillus are characterized by their relatively high milk clotting
activity and low proteolytic activity, which allow them to be used as
milk coagulants in cheese industry. Mutagenesis of these two enzymes
was performed by using the recombinant DNA technique to obtain
information on the structure-function relationship in this
characteristic group of the aspartic proteases
CONTINUOUS GLUCOSE MONITORING IN SUBCUTANEOUS TISSUE AND BLOOD WITH AN AMPEROMETRIC ENZYME ELECTRODE
No full textAs we have described previously, an amperometric enzyme electrode
was developed, based on the detection of hydrogen peroxide generated
by the oxidation of glucose (Kerner et al., Horm.Metab.Res.Suppl.20:
8-13,1988). This needle-type electrode was implanted into sc.tissue
of sheep. It is shown that the sensor current is closely related to
the course of blood glucose. For measurement of glucose in blood
comparable to the Biostator, an electrode was further modified and
integrated into a flow-chamber system. In vitro experiments demonstrated
its qualification. Monitoring of blood glucose was performed
over 24 hours
A NEW METHOD FOR DETERMINATION OF ENZYME SUBSTRATES BY MONITORING THE INTRINSIC FLUORESCENCE OF IMMOBILIZED ENZYMES
No full textWe describe a new method for monitoring the concentration of enzyme substrates that are
converted into products by an oxidation process. The method is based on the finding that enzymes
having FAD as a prosthetic group change their fluorescence during interaction with a
substrate. Typical enzymes that have been studied include glucose oxidase (GOD), lactate monooxygenase
(LMO), and cholesterol oxidase (ChOD). Their fluorescence is monitored via fiber
optic light guides at above 500 nm, following fluorescence excitation at around 410 - 450 nm.
The relative fluorescence intensities of the enzymes vary to a large extent, being highest for
LMO, and rather low for ChOD. Typical detection limits are in the 0.5 mM range for lactate
and 1.5 mM for glucose at ambient oxygen pressure.
A characteristic feature of this sensor is the narrow dynamic range which usually does not
exceed 3 mM.This is explained in terms of enzyme kinetics and diffusional processes. Unlike
optical biosensors based on measurementofthe intrinsic fluorescence of NADH, this sensor
type has the advantages of full reversibility (because reduced FAD-based enzymes accept oxygen
as a second substrate) and analytical wavelengths that are compatible with plastic or glass
fiber optics. The method has also been applied successfully in an FIA-like type of arrangement
L-LACTIC ACID DETERMINATIONIN MILK PRODUCTS BASED ONA FIBRE OPTIC BIOSENSOR AND FLOW INJECTION ANALYSIS(FIA)
No full textAnew methodfor the determinationof L -lactic acid using a fibre optic lactic acid biosensorin
combination with a flow injection system (FIA) is presented. The biosensoris based ona fibre
optic oxygen optrode which measures the oxygen consumption via dynamic quenching of the
fluorescence of a dye by molecular oxygen. Lactic acid oxidaseis immobilised onto the surface
of the oxygen optrode. For the detection of L- lactic acid in milk products, sample
pretreatment proved necessary for protection of the biosensor. As a consequencethe
samples were automatically diluted and buffered by meansof a FIA-system
A SURVEY OF FLAVOBACTERIUM
No full textThe survey of Flavobacterium is a general review of the origins of the genus and
of its taxonomic development in the various editions of Bergey's Manual. Brief consideration
is given to the chemistry of the pigments which have been studied