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De Vrese M.,Institute For Mikrobiologie Und Biotechnologie | Lorenzen P.,Institute For Sicherheit Und Qualitat Bei Milch Und Fisch | Clawin-Radecker I.,Institute For Sicherheit Und Qualitat Bei Milch Und Fisch | Hammer P.,Institute For Sicherheit Und Qualitat Bei Milch Und Fisch | And 4 more authors.
Ernahrungs Umschau | Year: 2012

The MRI performed a study on 30 milk samples, including traditional fresh milk, ESL milk and UHT milk. Whatever the processing procedure, all samples fulfilled expectations with respect to adequate heating of the milk, thermal stress, content of principle nutrients and - with a single exception - microbiological safety. No evidence at all was found of decreased vitamin content or increased losses on storage of properly stored ESL milk, in comparison to traditional (pasteurised) commercial milk. Pasteurised milk may have a marginally better taste and odour than ultrapasteurised milk, although the differences were not statistically significant. Moreover, there was no deterioration in the sensory quality of ESL milk after long-term storage. In summary, ESL milk is a high quality food, as judged by the criteria of nutritional physiology, and is comparable to traditional (pasteurised) fresh milk. It is nevertheless an open question whether milk that has been stored for up to 3 weeks fulfils the consumer's conception of "freshness" or "extended freshness", or whether it would perhaps be better just to speak of "extended shelf-life milk". Source


Heller K.J.,Institute For Mikrobiologie Und Biotechnologie | Neve H.,Institute For Mikrobiologie Und Biotechnologie
BioSpektrum | Year: 2014

Superinfection exclusion (SIE) is a mechanism by which a prophage residing in the genome of its host bacterium prevents infection of its host by other phages. During recent years, we have studied superinfection exclusion by prophage TP-J34. Its host is Streptococcus thermophilus J34, a bacterium applied as yoghurt starter. Here we present our data on identifying the SIE protein of TP-J34, its mode of action, X-ray structure, and target protein in the superinfecting phage. © 2014 Springer-Verlag Berlin Heidelberg. Literatur:. Source


Muhlig A.,TU Munich | Kabisch J.,Institute For Mikrobiologie Und Biotechnologie | Pichner R.,Institute For Mikrobiologie Und Biotechnologie | Scherer S.,TU Munich | Muller-Herbst S.,TU Munich
Food Microbiology | Year: 2014

The antimicrobial action of the curing agent sodium nitrite (NaNO2) in raw sausage fermentation is thought to mainly depend on the release of cytotoxic nitric oxide (NO) at acidic pH. Salmonella Typhimurium is capable of detoxifying NO via the flavohemoglobin HmpA, the flavorubredoxin NorV and the periplasmic cytochrome C nitrite reductase NrfA. In this study, the contribution of these systems to nitrosative stress tolerance in raw sausages was investigated. Invitro growth assays of the S. Typhimurium 14028 deletion mutants δhmpA, δnorV and δnrfA revealed a growth defect of δhmpA in the presence of acidified NaNO2. Transcriptional analysis of the genes hmpA, norV and nrfA in the wild-type showed a 41-fold increase in hmpA transcript levels in the presence of 150mg/l acidified NaNO2, whereas transcription of norV and nrfA was not enhanced. However, challenge assays performed with short-ripened spreadable sausages produced with 0 or 150mg/kg NaNO2 failed to reveal a phenotype for any of the mutants compared to the wild-type. Hence, none of the NO detoxification systems HmpA, NorV and NrfA is solely responsible for nitrosative stress tolerance of S. Typhimurium in raw sausages. Whether these systems act cooperatively, or if there are other yet undescribed mechanisms involved is currently unknown. © 2014 Elsevier Ltd. Source


Zeiser J.,Institute For Mikrobiologie Und Biotechnologie | Muhlenbeck L.H.,Institute For Mikrobiologie Und Biotechnologie | Schweiger P.,Missouri State University | Deppenmeier U.,Institute For Mikrobiologie Und Biotechnologie
Applied Microbiology and Biotechnology | Year: 2014

The α-proteobacterium Sphingomonas wittichii RW1 is known for its ability to degrade dioxins and related toxic substances. Bioinformatic analysis of the genome indicated that this organism may contain the largest number of pyrroloquinoline quinone-dependent dehydrogenases of any bacteria sequenced so far. Sequence analysis also showed that one of these genes (swit-4395) encodes an enzyme that belongs to the class of periplasmic glucose dehydrogenases. This gene was fused to a pelB signal sequence and a strep-tag coding region at the 5′ and 3′ ends, respectively. The fusion product was cloned into the broad-host range expression vector pBBR1p264-Streplong and the corresponding protein was heterologously produced in Escherichia coli, purified via Strep-Tactin affinity chromatography, and characterized. The protein Swit-4395 had a subunit mass of 39.3 kDa and formed active homooctamers and homododecamers. The enzyme showed the highest activities with short- and medium-chain aldehydes (chain length C1-C6) and ketoaldehydes, such as methylglyoxal and phenylglyoxal. Butyraldehyde was the best substrate, with Vmax and apparent KM values of 3,970 U/mg protein and 12.3 mM, respectively. Pyrroloquinoline quinone was detected using UV-Vis spectroscopy and was found to be a prosthetic group of the purified enzyme. Therefore, Swit-4395 was identified as a pyrroloquinoline quinone-dependent aldehyde dehydrogenase. The enzyme could be purified from the native host when the expression vector was introduced into S. wittichii RW1, indicating homologous protein production. Overproduction of Swit-4395 in S. wittichii RW1 dramatically increased the tolerance of the bacterium toward butyraldehyde and thus might contribute to the detoxification of toxic aldehydes. © 2013 Springer-Verlag. Source


Schweiger P.,Institute For Mikrobiologie Und Biotechnologie | Gross H.,Institute For Pharmazeutische Biologie | Deppenmeier U.,Institute For Mikrobiologie Und Biotechnologie
Applied Microbiology and Biotechnology | Year: 2010

Two cytosolic NADPH-dependent carbonyl reductases from Gluconobacter oxydans 621H, Gox0644 and Gox1615, were heterologously produced in Escherichia coli. The recombinant proteins were purified to homogeneity and characterized. Gox0644 and Gox1615 were dimers with native molecular masses of 66.1 and 74.5 kDa, respectively. The enzymes displayed broad substrate specificities and reduced α-ketocarbonyls at the keto moiety most proximal to the terminus of the alkyl chain to produce alpha-hydroxy carbonyls, as demonstrated by NMR. With respect to stereoselectivity, protein Gox0644 specifically reduced 2,3-pentanedione to 2R-hydroxy-pentane-3-one, whereas Gox1615 produced 2S-hydroxy-pentane-3-one. Both enzymes also reduced 1-phenyl-1,2-propanedione to 2-hydroxy-1-phenylpropane-1-one, which is a key intermediate in the production of numerous pharmaceuticals, such as antifungal azoles and antidepressants. Gox0644 displayed highest activities with 2,3-diones, α-ketoaldehydes, α-keto esters, and 2,5-diketogluconate. Gox1615 was less active with these substrates, but displayed a broader substrate spectrum reducing a variety of α-diketones and aldehydes. © 2010 Springer-Verlag. Source

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