Robert D. Trengove

Interactions between Wine Volatile Compounds and Grape and Wine Matrix Components Influence Aroma Compound Headspace Partitioning

A full-factorial design was used to assess the matrix effects of ethanol, glucose, glycerol, catechin, and proline on the volatile partitioning of 20 volatile compounds considered to play a role in wine aroma. Analysis of variance showed that the two-way interactions of ethanol and glucose, ethanol and glycerol, and glycerol and catechin significantly influenced headspace partitioning of volatiles. Experiments were conducted to observe the effect of varied ethanol and glucose concentrations on headspace partitioning of a constant concentration of volatiles. Analysis of variance and linear regression analysis showed that the presence of glucose increased the concentration of volatiles in the headspace, whereas increasing ethanol concentration was negatively correlated with headspace partitioning of volatiles. A subsequent study assessed the effect of diluting white and red wines with water and ethanol. It was again observed that increased ethanol concentration significantly reduced the relative abundance of volatile compounds in the sample headspace. This study investigates some of the complex matrix interactions of the major components of grape and wine that influence volatile compound headspace partitioning. The magnitude of each matrix-volatile interaction was ethanol > glucose > glycerol > catechin, whereas proline showed no apparent interaction. The results clearly identify that increasing ethanol concentrations significantly reduce the headspace concentration of volatile aroma compounds, which may contribute to explaining recent sensory research observations that indicate ethanol can suppress the fruit aroma attributes in wine.

Identification of alkyl substituted 2H-furo[2,3-c]pyran-2-ones as germination stimulants present in smoke.

The butenolide, 3-methyl-2H-furo[2,3-c]pyran-2-one (1), is a major compound in smoke responsible for promoting the seed germination of a wide range of plant species. We now report the structure of five alkyl substituted variants of 1 that are also present in smoke. The concentrations of these analogues, as well as that of 1, in a typical smoke-water solution have been determined using high-performance liquid chromatography (HPLC) purification followed by gas chromatography-mass spectrometry (GC-MS) analysis. The analogue, 3,5-dimethyl-2H-furo[2,3-c]pyran-2-one (3), was identified at levels that indicate that it is a contributor to the overall germination-promoting activity of crude smoke extracts.

Origins of Grape and Wine Aroma. Part 1. Chemical Components and Viticultural Impacts

Wine is an ancient beverage and has been prized throughout time for its unique and pleasing flavor. Wine flavor arises from a mixture of hundreds of chemical components interacting with our sense organs, producing a neural response that is processed in the brain and resulting in a psychophysical percept that we readily describe as “wine.” The chemical components of wine are derived from multiple sources; during fermentation grape flavor components are extracted into the wine and new compounds are formed by numerous chemical and biochemical processes. In this review we discuss the various classes of chemical compounds in grapes and wines and the chemical and biochemical processes that influence their formation and concentrations. The overall aim is to highlight the current state of knowledge in the area of grape and wine aroma chemistry.

Microvirga lupini sp. nov., Microvirga lotononidis sp. nov. and Microvirga zambiensis sp. nov. are alphaproteobacterial root-nodule bacteria that specifically nodulate and fix nitrogen with geographically and taxonomically separate legume hosts.

Strains of Gram-negative, rod-shaped, non-spore-forming bacteria were isolated from nitrogen-fixing nodules of the native legumes Listia angolensis (from Zambia) and Lupinus texensis (from Texas, USA). Phylogenetic analysis of the 16S rRNA gene showed that the novel strains belong to the genus Microvirga, with ≥ 96.1% sequence similarity with type strains of this genus. The closest relative of the representative strains Lut6(T) and WSM3557(T) was Microvirga flocculans TFB(T), with 97.6-98.0% similarity, while WSM3693(T) was most closely related to Microvirga aerilata 5420S-16(T), with 98.8% similarity. Analysis of the concatenated sequences of four housekeeping gene loci (dnaK, gyrB, recA and rpoB) and cellular fatty acid profiles confirmed the placement of Lut6(T), WSM3557(T) and WSM3693(T) within the genus Microvirga. DNA-DNA relatedness values, and physiological and biochemical tests allowed genotypic and phenotypic differentiation of Lut6(T), WSM3557(T) and WSM3693(T) from each other and from other Microvirga species with validly published names. The nodA sequence of Lut6(T) was placed in a clade that contained strains of Rhizobium, Mesorhizobium and Sinorhizobium, while the 100% identical nodA sequences of WSM3557(T) and WSM3693(T) clustered with Bradyrhizobium, Burkholderia and Methylobacterium strains. Concatenated sequences for nifD and nifH show that the sequences of Lut6(T), WSM3557(T) and WSM3693(T) were most closely related to that of Rhizobium etli CFN42(T) nifDH. On the basis of genotypic, phenotypic and DNA relatedness data, three novel species of Microvirga are proposed: Microvirga lupini sp. nov. (type strain Lut6(T) =LMG 26460(T) =HAMBI 3236(T)), Microvirga lotononidis sp. nov. (type strain WSM3557(T) =LMG 26455(T) =HAMBI 3237(T)) and Microvirga zambiensis sp. nov. (type strain WSM3693(T) =LMG 26454(T) =HAMBI 3238(T)).

Metabolite identification: are you sure? And how do your peers gauge your confidence?

Metabolomics is still faced with several significant challenges which currently limit its full scientific potential. The identification of metabolites is essential to convert analytical data into meaningful biological knowledge. However, identification confidence can vary widely because the process of identification is complex and dependent on the analytical platform and robustness of the methods applied, as well as the databases and resources used. Confident and unequivocal structure identification requires significant effort, which is multiplied dramatically in non-targeted metabolomics studies where 10–100s of metabolites can be deemed as biologically important and require identification. Mass spectrometry (MS), nuclear magnetic resonance spectroscopy (NMR) or integrated MS–NMR strategies (Dunn et al. 2013; Kind and Fiehn 2010; van der Hooft et al. 2011) provide much information for the identification of metabolites (e.g. 1D/2D-NMR and MS/MS).

Development of a sensitive non-targeted method for characterizing the wine volatile profile using headspace solid-phase microextraction comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry

Future understanding of differences in the composition and sensory attributes of wines require improved analytical methods which allow the monitoring of a large number of volatiles including those present at low concentrations. This study presents the optimization and application of a headspace solid-phase microextraction (HS-SPME) method for analysis of wine volatiles by comprehensive two-dimensional gas chromatography (GC×GC) time-of-flight mass spectrometry (TOFMS). This study demonstrates an important advancement in wine volatile analysis as the method allows for the simultaneous analysis of a significantly larger number of compounds found in the wine headspace compared to other current single dimensional GC-MS methodologies. The methodology allowed for the simultaneous analysis of over 350 different tentatively identified volatile and semi-volatile compounds found in the wine headspace. These included potent aroma compound classes such as monoterpenes, norisoprenoids, sesquiterpenes, and alkyl-methoxypyrazines which have been documented to contribute to wine aroma. It is intended that wine aroma research and wine sensory research will utilize this non-targeted method to assess compositional differences in the wine volatile profile.

Assessing the impact of transcriptomics, proteomics and metabolomics on fungal phytopathology

SUMMARY Peer-reviewed literature is today littered with exciting new tools and techniques that are being used in all areas of biology and medicine. Transcriptomics, proteomics and, more recently, metabolomics are three of these techniques that have impacted on fungal plant pathology. Used individually, each of these techniques can generate a plethora of data that could occupy a laboratory for years. When used in combination, they have the potential to comprehensively dissect a system at the transcriptional and translational level. Transcriptomics, or quantitative gene expression profiling, is arguably the most familiar to researchers in the field of fungal plant pathology. Microarrays have been the primary technique for the last decade, but others are now emerging. Proteomics has also been exploited by the fungal phytopathogen community, but perhaps not to its potential. A lack of genome sequence information has frustrated proteomics researchers and has largely contributed to this technique not fulfilling its potential. The coming of the genome sequencing era has partially alleviated this problem. Metabolomics is the most recent of these techniques to emerge and is concerned with the non-targeted profiling of all metabolites in a given system. Metabolomics studies on fungal plant pathogens are only just beginning to appear, although its potential to dissect many facets of the pathogen and disease will see its popularity increase quickly. This review assesses the impact of transcriptomics, proteomics and metabolomics on fungal plant pathology over the last decade and discusses their futures. Each of the techniques is described briefly with further reading recommended. Key examples highlighting the application of these technologies to fungal plant pathogens are also reviewed.

Effects of a butenolide present in smoke on light-mediated germination of Australian Asteraceae

This study investigated the effects of 3-methyl-2H-furo[2,3-c]pyran-2-one, a germination active butenolide present in plant-derived smoke, gibberellic acid and smoke water on seeds of Australian Asteraceae exposed to different light regimes. Seeds of all species required light, with maximum germination occurring under white light, or light dominated by 640 nm. Compared to untreated seeds, butenolide increased germination of Angianthus tomentosus, Gnephosis tenuissima, Myriocephalus guerinae, Podolepis canescens and Rhodanthe citrina at suboptimal light wavelengths and in the dark to a level equal to, or greater than, smoke water. Germination of Erymophyllum glossanthus and Gnephosis acicularis was not promoted by butenolide or smoke water under any light regime. The action of gibberellic acid was compared to that of butenolide for three species (Angianthus tomentosus, Myriocephalus guerinae and Podolepis canescens), and both compounds were found to stimulate germination. This study provides evidence that butenolide can act in a similar fashion as gibberellic acid in promoting seed germination of light-sensitive seeds. The ecological significance of these findings is discussed.

Burning vegetation produces cyanohydrins that liberate cyanide and stimulate seed germination

Cyanide is well known for its toxicity towards living organisms. Many plants use cyanide as a defensive agent against herbivores, releasing it through the enzymatic hydrolysis of endogenous cyanogenic compounds. At low concentrations, cyanide has been proposed to have a regulatory role in many plant processes including stimulation of seed germination. However, no ecological role for cyanide in seed germination has been established. In the present study, we show that burning plant material produces the cyanohydrin, glyceronitrile. We also show that, in the presence of water, glyceronitrile is slowly hydrolysed to release cyanide that stimulates seed germination of a diverse range of fire-responsive species from different continents. We propose that glyceronitrile serves as an ecological store for cyanide and is an important cue for stimulating seed germination and landscape regeneration after fires.

Mannitol is required for asexual sporulation in the wheat pathogen Stagonospora nodorum (glume blotch)

The physiological role of the mannitol cycle in the wheat pathogen Stagonospora nodorum (glume blotch) has been investigated by reverse genetics and metabolite profiling. A putative mannitol 2-dehydrogenase gene (Mdh1) was cloned by degenerate PCR and disrupted. The resulting mutated mdh1 strains lacked all detectable NADPH-dependent mannitol dehydrogenase activity. The mdh1 strains were unaffected for mannitol production but, surprisingly, were still able to utilize mannitol as a sole carbon source, suggesting a hitherto unknown mechanism for mannitol catabolism. The mutant strains were not compromised in their ability to cause disease or sporulate. To further our understanding of mannitol metabolism, a previously developed mannitol-1-phosphate dehydrogenase (gene mpd1) disruption construct [Solomon, Tan and Oliver (2005) Mol. Plant-Microbe Interact. 18, 110-115] was introduced into the mutated mdh1 background, resulting in a strain lacking both enzyme activities. The mpd1mdh1 strains were unable to grow on mannitol and produced only trace levels of mannitol. The double-mutant strains were unable to sporulate in vitro when grown on minimal medium for extended periods. Deficiency in sporulation was correlated with the depletion of intracellular mannitol pools. Significantly sporulation could be restored with the addition of mannitol. Pathogenicity of the double mutant was not compromised, although, like the previously characterized mpd1 mutants, the strains were unable to sporulate in planta. These findings not only question the currently hypothesized pathways of mannitol metabolism, but also identify for the first time that mannitol is required for sporulation of a filamentous fungus.