Aroma binding and stability in brewed coffee: A case study of 2-furfurylthiol.

The aroma stability of fresh coffee brew was investigated during storage over 60 min, there was a substantial reduction in available 2-furfurylthiol (2-FFT) (84%), methanethiol (72%), 3-methyl-1H-pyrole (68%) and an increase of 2-pentylfuran (65%). It is proposed that 2-FFT was reduced through reversible chemical binding and irreversible losses. Bound 2-FFT was released after cysteine addition, thereby demonstrating that a reversible binding reaction was the dominant mechanism of 2-FFT loss in natural coffee brew.

Acid production, growth kinetics and aroma profiles of Lactobacillus flora from Stilton cheese.

The effect of Lactobacillus plantarum isolates from Stilton cheese on aroma profiles of milk fermentation was examined. Representative Lb. plantarum isolates were cultured alone and in combination with acid-producing and non-acid producing Lactococcus lactis NCIMB 9918 in UHT milk at 30 & 18 °C for 48 h & 12 weeks, respectively in presence and absence of salt, simulating cheese production and ripening.

Development and validation of an APCI-MS/GC-MS approach for the classification and prediction of Cheddar cheese maturity.

Headspace techniques have been extensively employed in food analysis to measure volatile compounds, which play a central role in the perceived quality of food. In this study atmospheric pressure chemical ionisation-mass spectrometry (APCI-MS), coupled with gas chromatography-mass spectrometry (GC-MS), was used to investigate the complex mix of volatile compounds present in Cheddar cheeses of different maturity, processing and recipes to enable characterisation of the cheeses based on their ripening stages. Partial least squares-linear discriminant analysis (PLS-DA) provided a 70% success rate in correct prediction of the age of the cheeses based on their key headspace volatile profiles.

Diversity and activities of yeasts from different parts of a Stilton cheese.

Blue cheeses are very complex food matrices presenting significant spatial differentiation between sections and the Stilton variety also has a hard brown crust making its matrix even more complex. The mycobiota communities in the three sections (blue veins, white core and outer crust) of a Stilton blue cheese were studied by employing culture-independent (TRFLP, DGGE) and culture-dependent analyses. Yeasts isolated from the cheese were studied for aroma production in a dairy model system with and without the starter Lactococcus lactis and filamentous fungus Penicillium roqueforti using SPME GC-MS.

A female-emitted pheromone component is associated with reduced male courtship in the parasitoid wasp Spalangia endius.

During courtship interactions, the courted individual may not always be prepared to mate. For example, mating or courtship may be detrimental to its fitness and resistance is expected under these circumstances. As such, various resistance strategies have evolved, from physically fending off courting individuals to producing behavioural signals of unreceptivity.

Study of the influence of yeast inoculum concentration (Yarrowia lipolytica and Kluyveromyces lactis) on blue cheese aroma development using microbiological models.

Yarrowia lipolytica and Kluyveromyces lactis occur as part of Stilton cheese microflora yet are not controlled during production. This study investigated the influence of their inoculum concentration on aroma production. Models of Y.

Flavour generation during commercial barley and malt roasting operations: a time course study.

The roasting of barley and malt products generates colour and flavour, controlled principally by the time course of product temperature and moisture content. Samples were taken throughout the industrial manufacture of three classes of roasted product (roasted barley, crystal malt and black malt) and analysed for moisture content, colour and flavour volatiles. Despite having distinct flavour characteristics, the three products contained many compounds in common.

Effects of ethanol and long-chain ethyl ester concentrations on volatile partitioning in a whisky model system.

Ethanolic atmospheric pressure chemical ionization mass spectrometry (APCI-MS) was used to analyze the headspace concentrations of a test set of 14 whisky volatile compounds above a series of aqueous ethanolic solutions differing in alcohol content (5-40% ABV) and with regard to concentration of ethyl hexadecanoate (0-500 mg/L). The latter was selected to represent the long-chain ethyl esters found at various concentrations in new-make spirit. Headspace ion intensities were modeled against ethanol and ethyl hexadecanoate concentrations as factors.

Aroma release from wines under dynamic conditions.

Aroma release from wines and model ethanolic solutions during dynamic headspace dilution was measured in real time using atmospheric pressure chemical ionization-mass spectrometry. Model ethanolic solutions maintained the headspace concentration of volatile compounds close to equilibrium values during gas phase dilution over 10 min. Wine samples (with the same ethanol content) did not maintain the headspace concentration of volatiles to the same extent.

Carbohydrate utilization and the lager yeast transcriptome during brewery fermentation.

The fermentable carbohydrate composition of wort and the manner in which it is utilized by yeast during brewery fermentation have a direct influence on fermentation efficiency and quality of the final product. In this study the response of a brewing yeast strain to changes in wort fermentable carbohydrate concentration and composition during full-scale (3275 hl) brewery fermentation was investigated by measuring transcriptome changes with the aid of oligonucleotide-based DNA arrays. Up to 74% of the detectable genes showed a significant (p View Article and Find Full Text PDF

Effect of ethanol, temperature, and gas flow rate on volatile release from aqueous solutions under dynamic headspace dilution conditions.

On the basis of a mechanistic model, the overall and liquid mass transfer coefficients of aroma compounds were estimated during aroma release when an inert gas diluted the static headspace over simple ethanol/water solutions (ethanol concentration = 120 mL x L(-1)). Studied for a range of 17 compounds, they were both increased in the ethanol/water solution compared to the water solution, showing a better mass transfer due to the presence of ethanol, additively to partition coefficient variation. Thermal imaging results showed differences in convection of the two systems (water and ethanol/water) arguing for ethanol convection enhancement inside the liquid.

The oxidative stress response of a lager brewing yeast strain during industrial propagation and fermentation.

Commercial brewing yeast strains are exposed to a number of potential stresses including oxidative stress. The aim of this investigation was to measure the physiological and transcriptional changes of yeast cells during full-scale industrial brewing processes with a view to determining the environmental factors influencing the cell's oxidative stress response. Cellular antioxidant levels and genome-wide transcriptional changes were monitored throughout an industrial propagation and fermentation.

In vivo flavor release from gelatin-sucrose gels containing droplets of flavor compounds.

Gelatin-sucrose gels containing the same amount of flavor compounds present as either suspended droplets or homogenously distributed in the gel (dissolved) were eaten, and the in vivo flavor release was studied using atmospheric pressure chemical ionization-mass spectrometry. The maximum intensity of release was higher from all droplet-containing samples as compared with the dissolved sample (by a factor of 4-2500-fold). When the flavor was dispersed as a greater number of smaller droplets rather than one 1 microL droplet, the intensity of in vivo release was slightly lower.

Redirection of carotenoid metabolism for the efficient production of taxadiene [taxa-4(5),11(12)-diene] in transgenic tomato fruit.

The taxanes are a group of polycyclic diterpenes produced by various species of yew. The potent anticancer drug paclitaxel (marketed as Taxol) is the commercially most important taxane with annual sales in 2000 exceeding 1.6 billion dollars.

Volatile emission by contest losers revealed by real-time chemical analysis.

Animal interactions often involve chemical exchange but simultaneous evaluation of chemistry and behaviour has been problematical. Here we report findings from a novel method, atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) coupled with manipulation of molecular-mass achieved by rearing organisms on deuterium-enhanced nutrients. This allows real-time monitoring of the occurrence and quantity of volatile chemicals released by each of two interacting individuals, in tandem with behavioural observations.

Dynamic headspace analysis of the release of volatile organic compounds from ethanolic systems by direct APCI-MS.

Static equilibrium headspace was diluted with a stream of nitrogen to study the stability of the volatile headspace concentration. The headspace dilution profile of 18 volatile compounds above aqueous and ethanolic solutions was measured in real time using atmospheric pressure chemical ionization-mass spectrometry. Under dynamic conditions the volatiles headspace concentration above water solutions decreased readily upon dilution.

Model studies on retention of added volatiles during breadcrumb production.

Breadcrumb samples were prepared with a range of volatile compounds at known concentrations. The retention of these volatiles was assessed via solvent extraction and quantification by gas chromatography-mass spectrometry. Volatile loss during processing was shown to be substantial and dependent upon the compound's vapor pressure.

Direct coupling of supercritical fluid extraction to a gas phase atmospheric pressure chemical ionisation source ion trap mass spectrometer for fast extraction and analysis of food components.

Supercritical fluid extraction (SFE) was coupled to a custom-built atmospheric pressure chemical ionization (APCI) source of an ion trap mass spectrometer (ITMS). This method was developed for the monitoring of static or dynamic carbon dioxide extraction of volatile aroma compounds in real time. The gas phase APCI source resulted in simple spectra where the extraction of individual compounds could be monitored.

Effect of beta-cyclodextrin on aroma release and flavor perception.

Binding and release of volatile compounds to and from beta-cyclodextrin were measured in model aqueous systems using static equilibrium headspace and dynamic headspace dilution. Beta-cyclodextrin decreased the static equilibrium headspace for some volatiles (e.g.

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.

Effects of hydrocolloid thickeners on the perception of savory flavors.

The perceived intensities of savory flavors in hydrocolloid-thickened solutions were investigated using sensory paired comparison tests between two distinct thickener concentrations (high and low viscosities). The perceived saltiness of 3.5 g/L NaCl was found to be significantly reduced (P < 0.

Oral shear stress predicts flavour perception in viscous solutions.

The perception of sweetness and flavour were studied in viscous solutions containing 50 g/l sucrose, 100 p.p.m.

Monitoring chemical and physical changes during thermal flavor generation.

On-line techniques were developed to monitor chemical and physical changes occurring during the heating of skim milk powder (SMP). Atmospheric pressure chemical ionization mass spectrometry (APCIMS) followed the generation and release of volatile compounds from SMP in a packed-bed reactor. Operating conditions were optimized to avoid condensation of high boiling compounds such as maltol, and the system was highly reproducible (CV < 7%).

Real-time monitoring of thermal flavor generation in skim milk powder using atmospheric pressure chemical ionization mass spectrometry.

The feasibility of monitoring volatile flavor compounds formed by thermal treatment of skimmed milk powder in real time by atmospheric pressure chemical ionization mass spectrometry (APCIMS) was established. Skim milk powder samples were heated isothermally (70 to 120 degrees C) at different moisture contents (2.2 and 12.

Modeling the partition of volatile aroma compounds from a cloud emulsion.

Parameters determining the partitioning behavior of volatile compounds between a cloud emulsion and the gas phase were measured under static equilibrium headspace conditions, using volatiles (e.g., ethyl hexanoate, cymene, and octanol) representing different volatilities and different degrees of hydrophobicity.