Biomedical subjects

Ulrich Krings

Publications and source records attributed to Ulrich Krings.

12 recordsLinked to original sources

PubMed2006

Odor-active alcohols from the fungal transformation of alpha-farnesene.

Submerged microbial cultures were screened for their potential to oxifunctionalize alpha-farnesene. The major oxidation product in all transforming cultures, 3,7,11-trimethyldodeca-1,3(E),5(E)10-tetraen-7-ol, showed a pleasant citrus-like odor and peak concentrations of 170 mg L-1. An Aspergillus niger isolate from mango generated another two terpene alcohols identified as diastereomeric menth-1-en-3-[2-methyl-1,3-butadienyl]-8-ol, a new natural compound with an apricot-like odor. The regiospecifity of the oxygen attack with concurrent lack of stereoselectivity suggested that the initial step of the bioconversion resembled the chemical autoxidation starting with the generation of an intermediate resonance-stabilized carbon-centered radical or carbocation.

Alcohols↗

PubMed2005

Characteristic volatiles from young and aged fruiting bodies of wild Polyporus sulfureus (Bull.:Fr.) Fr.

The volatile compounds of fresh fruiting bodies of wild Polyporus sulfureus (Bull.:Fr.) Fr. growing on oak trees were isolated by continuous liquid-liquid extraction (CLLE) and investigated by high-resolution gas chromatography-mass spectrometry (HRGC-MS) on two GC columns of different polarity (DB-5 and ZB-WAX), and by gas chromatography-olfactometry (GC-O). A total of 40 major volatile compounds from the young samples were identified and semiquantified. Five odorous compounds were determined to be responsible for the characteristic flavor of young Polyporus sulfureus: 1-octen-3-one, 1-octen-3-ol, 3-methylbutanoic acid, phenylethanol, and phenylacetic acid. Four volatiles investigated by GC-O and detected by GC-MS were determined as the characteristic odorants of aged species: 2-methylpropanoic acid, butanoic acid, 3-methylbutanoic acid, and phenylacetic acid. The comparative results revealed that the volatile composition of the fruiting bodies even from the same fungal species may greatly vary with its host, location, and age.

Chromatography, Gas↗

PubMed2004

Bioconversion of (+)-valencene in submerged cultures of the ascomycete Chaetomium globosum.

Submerged cultures of the ascomycete Chaetomium globosum oxidised the exogenous sesquiterpene (+)-valencene to nootkatone via the stereoselective generation of alpha-nootkatol. Inhibition experiments suggested that the first introduction of oxygen, the rate-limiting step of the bioconversion, may have been catalysed by a cytochrome-P450-monooxygenase. However, nootkatone was not the final metabolite: further flavour-active and inactive, non-volatile oxidation products were identified. (+)-Valencene and the flavour-active mono-oxyfunctionalised transformation products, alpha-nootkatol, nootkatone, and valencene-11,12-epoxide accumulated preferably inside the fungal cells. Di- and poly-oxygenated products, such as nootkatone-11,12-epoxide, were found solely in the culture medium, indicating an active transport of these metabolites into the extracellular compartment during (+)-valencene detoxification. These metabolic properties may have contributed to the high tolerance of the fungus towards the exogenous hydrocarbon.

Biotechnology↗

PubMed2004

In vitro study of the influence of physiological parameters on dynamic in-mouth flavour release from liquids.

Influences of shear rate (surface extension), airflow, in-mouth headspace volume, synthetic saliva and human epithelial cells (modelling mucosa) on the initial dynamic flavour release from liquids were analysed. Simulating physiological mouth parameters, initial dynamic flavour release experiments over a time period of 30 s were carried out using a proven mouth model apparatus. Flavour compounds of different chemical classes were dissolved in water or in aqueous starch hydrolysate in concentrations typically present in food ( micro g/l to mg/l). Forced by increasing shear rates the enlargement of the gas-liquid interface (vortex formation) caused an increased release of flavour molecules. The release of less soluble compounds was reduced by increasing shear forces due to an improved dissolution. Increasing volumetric airflow rates resulted generally in higher release rates and in a change of pattern of release kinetics. Maximum flavour release was found at a ratio of 1:1 for in-mouth headspace and liquid volume. Neither addition of saliva alone nor the combination of saliva and mucosa showed significant influence on in-mouth flavour release from liquids in the model mouth.

Chromatography, Gas↗

PubMed2004

Volatile release from liquids: a comparison of in vivo APCI-MS, in-mouth headspace trapping and in vitro mouth model data.

In-mouth volatile release from flavoured water was followed using atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) or using a hand-held, computer-controlled device based on sequential trapping of flavours on Tenax traps. The present results verify recent in vitro data obtained with a sophisticated, fully computerized mouth model apparatus and confirm its validity for the simulation of in-mouth dynamic volatile release. In-nose APCI-MS measurements showed considerable person-to-person variability in non-trained individuals during drinking due to subconscious control of muscles during swallowing and subsequent breathing. Data showed a 'swallow breath' volume reaching the nasal cavity from the throat, not from the mouth cavity. Flavour enriched air from the mouth was shown to be transported to the nose (via exhalation) immediately after the swallowing event, but the dynamic process of volatile equilibration between residuals of the swallowed liquid and the exhaled air predominantly determined volatile in-nose concentration. Owing to its dynamic character, the process of volatile equilibration and release in the throat upon exhalation should be similar to the in-mouth process studied in the present work. A full mechanical simulation of retronasal volatile transport, however, will remain difficult.

Beverages↗

PubMed2003

Dynamic flavor release from sucrose solutions.

The initial dynamic flavor release from sucrose solutions was modeled. Modeling was based on the theoretical hydration behavior of sucrose, theoretical physicochemical data of flavor volatiles, and process parameters of a headspace apparatus used for model validation. The rate-limiting factor determining the initial flavor release was the hydration of sucrose, which in turn depends on the molarity of sucrose in the solution and, therefore, on the actual amount of nonbound water. Improved solubility of the more hydrophilic compounds due to their orientation toward the hydration shells of the sugar molecules was considered. The viscosity of nonassociated water forming the microregion for mass transfer of volatiles was considered instead of the bulk solution viscosity. Experimental validation of the model by real-time measurements of dynamic flavor release using foodlike flavor concentrations confirmed the above theory. Increasing sucrose concentrations resulted predominantly in increased flavor release, and bulk solution viscosity showed no effect.

Chemical Phenomena↗

PubMed2003

Lipid molarity affects liquid/liquid aroma partitioning and its dynamic release from oil/water emulsions.

Initial dynamic flavor release from oil/water emulsions containing different TAG phases was studied using a computerized apparatus and thermodesorption GC. A significant influence of lipid molarity on liquid/liquid partitioning and release of some flavor compounds was found. The release of the least hydrophobic compounds was not affected by any type of lipid. Hydrophobic compounds showed a positive correlation between their release and decreasing molarity of the lipid phase, that is, with increasing number of lipid molecules; only the most hydrophobic compounds did not show such a correlation. A strong linear correlation between low-melting TAG/water partition coefficients and lipid phase molarity was validated by volatile partition data of C6, C11, and C16 alkane/water systems. Lipid phase transition from the liquid to solid state did not affect flavor partitioning and release. Neither experimental nor theoretical octanol/water partition coefficients agreed with experimental TAG/water and alkane/water partition coefficients.

Emulsions↗

PubMed2002

Computerized apparatus for measuring dynamic flavor release from liquid food matrices.

A fully computer-controlled apparatus was designed. It combines a glass reactor with a temperature-controlled hood, in which headspace volatiles are captured. Flavored liquids can be introduced into the reactor and exposed to conditions of temperature, air flow, shear rate, and saliva flow as they occur in the mouth. As the reactor is completely filled before measurements are started, creation of headspace just before sampling start prevents untimely flavor release resulting in real time data. In the first 30 s of flavor release the concentrations of the volatiles can be measured up to four times by on-line sampling of the dynamic headspace, followed by off-line trapping of the samples on corresponding Tenax traps and analysis using GC-TDS-FID. Flavor compounds from different chemical classes were dissolved in water to achieve concentrations typically present in food (micrograms to milligrams per liter). Most of the compounds showed constant release rates, and the summed quantities of each volatile of three 10 s time intervals correlated linearly with time. The entire method of measurement including sample preparation, release, sampling, trapping, thermodesorption, and GC analysis showed good sensitivity [nanograms (10 s)(-1)] and reproducibility (mean coefficient of variation = 7.2%).

Chromatography, Gas↗

PubMed2002

Modeling dynamic flavor release from water.

A mathematical model derived from the convective mass transfer theory was developed to predict dynamic flavor release from water. A specific mass transfer correlation including a new term for volatile permeability was applied. The model was entirely based on physicochemical constants of flavor compounds and on some parameters of an apparatus used for validation. The model predicted a linear pattern of release kinetics during the first 30 s and large differences of absolute release for individual compounds. Both calculated and experimentally determined release profiles of a test mixture of flavors showed good agreement.

Kinetics↗

PubMedDate not supplied

GC/MS analysis of some bioactive constituents from Carthamus lanatus L.

Sterols, triterpenes, volatiles, polar and other constituents in aerial parts of Carthamus lanatus were analyzed by gas chromatography-mass spectrometry. Over 90 compounds were identified most of them new for the species. Sitosterol and stigmasterol were the most abundant of 10 sterols identified in the sterol fraction. Taraxasterol, alpha- and beta-amyrine prevailed in the triterpene fraction. Volatiles, sterols and a fraction of the dichloromethane extract showed strong cytotoxicity (Artemia salina assay).

Animals↗

PubMedDate not supplied

Regio- and stereoselective fungal oxyfunctionalisation of limonenes.

Selective transformations of limonene by asco- and basidiomycetes were investigated. On the shake flask scale, Penicillium citrinum hydrated R-(+)-limonene to a-terpineol [83% regioselectivity (rs), more than 80 mg l(-1) product yield], and Gongronella butleri catalysed the terminal oxidation to yield perillyl alcohol (60% rs, 16 mg l(-1)). On the laboratory bioreactor scale, Penicillium digitatum produced a peak concentration of 506 mg a-terpineol l(-1) in the fed-batch mode, equivalent to a theoretical yield of 67%, and no volatile by-products were found. Fusarium proliferatum transformed R-(+)-limonene enantiospecifically to cis-(+)-carveol (98.6% ee, more than 35 mg l(-1) product yield) and S-(-)-limonene predominantly to trans-(-)-carveol (96.3% ee). Pleurotus sapidus selectively dehydrogenised the accumulating trans-(-)-carveol to the corresponding enantiopure R-(-)-carvone. The results show that a careful selection of strain and bioprocess parameters may improve both the yield and the optical purity of a desired product.

Ascomycota↗

PubMedDate not supplied

A comparison of cell wall disruption techniques for the isolation of intracellular metabolites from Pleurotus and Lepista sp.

Different techniques were compared for their effectiveness in the disruption of the rigid cell walls of Basidiomycetes. Grinding under liquid nitrogen, stirred glass bead milling and enzymatic cell lysis were applied to the mycelia of Pleurotus sapidus and Lepista irina grown submerged. Each of the disruption procedures was evaluated by testing the quantity and quality of released intracellular metabolites: DNA, RNA, enzymes, and secondary metabolites. The most suitable method for nucleic acid isolation was grinding under liquid nitrogen, while bead mill homogenization was the superior technique for isolation of active enzymes. A new effective method is proposed for isolation of secondary metabolites with the aid of bead milling of fungal mycelia.

Agaricales↗