Barbara Siegmund

Monitoring the plant epiphyte Methylobacterium extorquens DSM 21961 by real-time PCR and its influence on the strawberry flavor

Besides its influence on plant growth and health, plant-associated bacteria exert an impact on fruit quality. Methylotrophic bacteria can enhance the biosynthesis of strawberry flavor compounds, especially the two furanoid compounds 2,5-dimethyl-4-hydroxy-2H-furanone (DMHF) and 2,5-dimethyl-4-methoxy-2H-furanone in vitro. Here, we report the selection and characterization of Methylobacterium extorquens DSM 21961, a strain that was able to enhance the furanone content ad planta under greenhouse conditions. For monitoring the colonization of strawberry plants, a strain-specific quantification system for M. extorquens DSM 21961 was developed. Specificity, linear range and quantitative limit of the system were shown, and successful application was demonstrated in a monitoring experiment of M. extorquens DSM 21961 on strawberry leaves under greenhouse conditions. Furthermore, the quantification of DMHF in strawberry fruits via GC indicated an increased biosynthesis of this compound in strawberry plants. The colonization behavior analyzed by confocal laser scanning microscopy using GFP-tagged cells revealed high colonization of the upper and the lower leaf surfaces, with a specific accumulation of bacterial cells on trichomes. The results support a biotechnological application of this promising flavor-stimulating agent.

Key odourants of pressure-cooked hen meat

Abstract The volatile aroma compounds of pressure-cooked hen meat isolated by simultaneous distillation-extraction and extraction-high vacuum distillation were investigated by GC/MS and GC-olfactometry. We found out that 2-furfuryl thiol, 3-(methylthio)propanal, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, (E,E)-2, 4-decadienal, 2-methyl-3-furanthiol and 2-ethyl-3,5-dimethyl pyrazine are the most potent odourants of the pressure-cooked hen meat. We assume that aroma-active compounds such as 2,4,6-trimethyltetrahydro-1,3,5-thiadiazine, 3,5-dime-thyl-1, 2,4-trithiolane, 5,6-dihydro-2,4,6-trimethyl-4H-1,3,5-dithiazine and some unknown compounds, which could only be found in extracts obtained by simultaneous distillation-extraction, are artefacts formed during this isolation process.

Study of the influence of maceration time and oenological practices on the aroma profile of Vranec wines.

Vranec is one of the most important red grape varieties in Republic of Macedonia, grown in all vineyards, mostly in the Tikveš wine region. In this study, Vranec wines produced with different maceration times (4, 7, 14 and 30 days) in presence of enzyme and oak chips during fermentation were studied in order to determine the influence of vinification conditions on the aroma profile. The volatile compounds were determined using headspace solid phase microextraction (HS-SPME) with a PDMS/Carboxen/DVB fibre, coupled with gas chromatography-mass spectrometry (GC-MS). In total 63 aroma compounds were detected revealing a complex aroma profile of Vranec wines composed of esters, alcohols, fatty acids, aldehydes, ketones and sulphur compounds. The content of aroma compounds was related mostly to maceration time, observing increased relative amount of alcohols, esters and fatty acids from the fourth to seventh day of maceration and the presence of oak chips during the fermentation enhanced their formation. The Student-Newman-Keuls test has been applied to ascertain possible significant differences between the studied wines, and principal component analysis has been employed, showing separation and grouping of the wines according to maceration time and oak chips treatment.

Development of a simple sample preparation technique for gas chromatographic-mass spectrometric determination of nicotine in edible nightshades (Solanaceae).

The purpose of this study was to develop a rapid analytical method for the reliable determination of low concentrations of nicotine in foods for large numbers of samples. Food material was extracted using a simple liquid-liquid extraction method. For processed foods, further clean-up steps had to be employed to eliminate interfering compounds. The determination of nicotine was performed by gas chromatography-mass spectrometry. Quantitative analysis was accomplished using deuterium labeled nicotine as an internal standard. Recoveries of over 95% were obtained for a single step extraction, as well as for a multiple-stage extraction procedure, respectively. The method has been applied to the determination of nicotine in edible nightshades (i.e. tomatoes, potatoes and aubergines) and their processed products.

The contribution of dietary nicotine and dietary cotinine to salivary cotinine levels as a nicotine biomarker

Abstract Dietary nicotine, as a source of nicotine biomarkers such as salivary cotinine, has been a controversial topic, mainly because of limited published data on nicotine in foods. Recently, a sample preparation method for nicotine in foods and an analytical method, based on gas chromatography with mass spectrometric detection, were developed and validated in our laboratory. Nicotine was determined in fresh, cooked and processed foods of the Solanaceae family. In this study we have furthered this work to investigate the presence of cotinine in these vegetables, using GC–MS and HPLC–MS as independent alternative analytical techniques. A large number of samples was investigated, but cotinine was not detected in any of the samples, although very high sensitivity could be achieved. Based on the results, we report a Monte Carlo simulation of salivary cotinine levels obtained utilising dietary nicotine, food consumption data, and the variance in these parameters. In this estimate, a mean salivary cotinine concentration of 0.022 ng ml −1 is predicted from dietary sources. This level is below the limit of detection for traditional analytical methods, but perhaps not for newly-developed methods.

Determination of sulfur and nitrogen compounds during the processing of dry fermented sausages and their relation to amino acid generation

The identification of odor-active sulfur and nitrogen compounds formed during the processing of dry fermented sausages was the objective of this study. In order to elucidate their possible origin, free amino acids (FAAs) were also determined. The volatile compounds present in the dry sausages were extracted using solvent assisted flavor evaporation (SAFE) and monitored by one and two-dimensional gas chromatography with different detectors: mass spectrometry (MS), nitrogen phosphorous (NPD), flame photometric (FPD) detectors, as well as gas chromatography-olfactometry. A total of seventeen sulfur and nitrogen compounds were identified and quantified. Among them, 2-acetyl-1-pyrroline was the most potent odor active compound, followed by methional, ethylpyrazine and 2,3-dihydrothiophene characterized by toasted, cooked potato, and nutty notes. The degradation of FAAs, generated during processing, was related to the production of aroma compounds, such as methionine forming methional and benzothiazole while ornithine was the precursor compound for 2-acetyl-1-pyrroline and glycine for ethylpyrazine.

More than Honey: Investigation on Volatiles from Monovarietal Honeys Using New Analytical and Sensory Approaches

Eight monovarietal honeys from dandelion, fir tree, linden tree, chestnut tree, robinia, orange, lavender, and rape were investigated with respect to their volatile compounds and sensory properties. Analysis of the volatile compounds was performed by gas chromatographic techniques (one-dimensional GC-MS as well as comprehensive GC×GC-MS). For sensory evaluation Napping in combination with ultraflash profiling was applied using sensory experts. For dandelion honey, 34 volatile compounds are described for the first time to be present in dandelion honey. PCA and cluster analysis of the volatile compounds, respectively, show high correlation with the PCA obtained from sensory evaluation. Lavender and linden honey showed sensory characteristics that were not expected from these honey types. Analysis of the volatile compounds resulted in the identification of odor-active compounds that are very likely derived from sources other than the respective honeyflow. Contamination with essential oils used in apiculture is very likely to be the reason for the occurrence of these compounds in the investigated honeys.

The Flavor of Elderflower – Species Differentiation via Flavor Compounds

The very pleasant flavor of elder flowers (Sambucus niger L.) was the focus of this study. The flavor compounds of elder flowers of various varieties obtained from different growing sites were investigated over a period of 3 years. The flowers were analyzed by headspace SPME and subsequent GC-MS. Multivariate analysis of the data showed that there are significant differences in the composition of the volatile compounds depending on the elder variety, whereas differences based on the growing site and the year of vegetation play a minor role. Wild forms cannot be related to any distinct elder variety via the flavor profile.

The Effect of Methylobacteria Application on Strawberry Flavor Investigated by GC-MS and Comprehensive GC×GC-qMS

The flavor of strawberries (Fragaria ananassa) and the influence of the mutualistic association between the strawberry plant and methylobacteria on strawberry flavor formation in the fruit were the focus of this study. With the aim of better understanding the underlying reactions and their influence on strawberry flavor formation, we investigated strawberries that were treated with methylobacteria as well as fruits from control plants by the use of comprehensive GC×GC-qMS in comparison to traditional GC-MS. For various reasons, the preliminary results did not provide any clear explanation of what happens in this specific plant–bacteria association; further efforts are therefore required in plant breeding as well as in analytical investigations.

Formation and determination of microbially-derived off-flavour in apple juice

The role of two bacteria (namely Alicyclobacillus acidoterrestris and Streptomyces griseus griseus) on the off-flavour formation in apple juice was investigated. The strains were able to form a number of off-flavour compounds causing medicinal and/or earthymusty notes in the juice under conditions that were common for the storage of shelf-stable products.