Aerial and underground organs display specific metabolic strategies to cope with water stress under rising atmospheric CO2 in Fagus sylvatica L.

Beech is known to be a moderately drought-sensitive tree species, and future increases in atmospheric concentrations of CO2 ([CO2 ]) could influence its ecological interactions, also with changes at the metabolic level. The metabolome of leaves and roots of drought-stressed beech seedlings grown under two different [CO2 ] (400 (aCO2 ) and 800 (eCO2 ) ppm) was analyzed together with gas exchange parameters and water status. Water stress estimated from predawn leaf water potential (Ψpd ) was similar under both [CO2 ], although eCO2 had a positive impact on net photosynthesis and intrinsic water use efficiency. The aerial and underground organs showed different metabolomes. Leaves mainly stored C metabolites, while those of N and P accumulated differentially in roots. Drought triggered the proline and N-rich amino acids biosynthesis in roots through the activation of arginine and proline pathways. Besides the TCA cycle, polyols and soluble sugar biosynthesis were activated in roots, with no clear pattern seen in the leaves, prioritizing the root functioning as metabolites sink. eCO2 slightly altered this metabolic acclimation to drought, reflecting mitigation of its effect. The leaves showed only minor changes, investing C surplus in secondary metabolites and malic acid. The TCA cycle metabolites and osmotically active substances increased in roots, but many other metabolites decreased as if the water stress was dampened. Above- and belowground plant metabolomes were differentially affected by two drivers of climate change, water scarcity and high [CO2 ], showing different chemical responsiveness that could modulate the tree adaptation to future climatic scenarios.

Specific leaf metabolic changes that underlie adjustment of osmotic potential in response to drought by four Quercus species.

Osmotic adjustment is almost ubiquitous as a mechanism of response to drought in many forest species. Recognized as an important mechanism of increasing turgor under water stress, the metabolic basis for osmotic adjustment has been described in only a few species. We set an experiment with four species of the genus Quercus ranked according to drought tolerance and leaf habit from evergreen to broad-leaved deciduous. A cycle of watering deprivation was imposed on seedlings, resulting in well-watered (WW) and water-stressed (WS) treatments, and their water relations were assessed from pressure-volume curves. Leaf predawn water potential (Ψpd) significantly decreased in WS seedlings, which was followed by a drop in leaf osmotic potential at full turgor (Ψπ100). The lowest values of Ψπ100 followed the ranking of decreasing drought tolerance: Quercus ilex L. < Quercus faginea Lam. < Quercus pyrenaica Willd. < Quercus petraea Matt. Liebl. The leaf osmotic potential at the turgor loss point (ΨTLP) followed the same pattern as Ψπ100 across species and treatments. The pool of carbohydrates, some organic acids and cyclitols were the main osmolytes explaining osmotic potential across species, likewise to the osmotic adjustment assessed from the decrease in leaf Ψπ100 between WW and WS seedlings. Amino acids were very responsive to WS, particularly γ-aminobutyric acid in Q. pyrenaica, but made a relatively minor contribution to osmotic potential compared with other groups of compounds. In contrast, the cyclitol proto-quercitol made a prominent contribution to the changes in osmotic potential regardless of watering treatment or species. However, different metabolites, such as quinic acid, played a more important role in osmotic adjustment in Q. ilex, distinguishing it from the other species studied. In conclusion, while osmotic adjustment was present in all four Quercus species, the molecular processes underpinning this response differed according to their phylogenetic history and specific ecology.

Rising [CO2] effect on leaf drought-induced metabolome in Pinus pinaster Aiton: Ontogenetic- and genotypic-specific response exhibit different metabolic strategies.

Rising atmospheric CO2 concentrations ([CO2]) together with water deficit can influence ecological interactions of trees through an array of chemically driven changes in plant leaves. In four drought stressed Pinus pinaster genotypes, grown under two levels of atmospheric [CO2] (ambient (aCO2) and enriched (eCO2)) the metabolome of adult and juvenile needles was analyzed to know if the metabolic responses to this environmental situation could be genotype-dependent and vary according to the stage of needle ontogeny. Drought had the highest incidence, followed by needle ontogeny, being lower the eCO2 effect. The eCO2 reduced, eliminated or countered the 50 (adult needles) - 44% (juvenile) of the drought-induced changes, suggesting that CO2-enriched plants could perceived less oxidative stress under drought, and proving that together, these two abiotic factors triggered a metabolic response different from that under single factors. Genotype drought tolerance and ontogenetic stage determined the level of metabolite accumulation and the plasticity to eCO2 under drought, which was mainly reflected in antioxidant levels and tree chemical defense. At re-watering, previously water stressed plants showed both, reduced C and N metabolism, and a "drought memory effect", favoring antioxidants and osmolyte storage. This effect showed variations regarding genotype drought-tolerance, needle ontogeny and [CO2], with remarkable contribution of terpenoids. Chemical defense and drought tolerance were somehow linked, increasing chemical defense during recovery in the most drought-sensitive individuals. The better adaptation of trees to drought under eCO2, as well as their ability to recover better from water stress, are essential for the survival of forest trees.

Leaf ecophysiological and metabolic response in Quercus pyrenaica Willd seedlings to moderate drought under enriched CO2 atmosphere.

Impact of drought under enriched CO2 atmosphere on ecophysiological and leaf metabolic response of the sub-mediterranean Q. pyrenaica oak was studied. Seedlings growing in climate chamber were submitted to moderate drought (WS) and well-watered (WW) under ambient ([CO2]amb =400 ppm) or CO2 enriched atmosphere ([CO2]enr =800 ppm). The moderate drought endured by seedlings brought about a decrease in leaf gas exchange. However, net photosynthesis (Anet) was highly stimulated for plants at [CO2]enr. There was a decrease of the stomatal conductance to water vapour (gwv) in response to drought, and a subtle trend to be lower under [CO2]enr. The consequence of these changes was an important increase in the intrinsic leaf water use efficiency (WUEi). The electron transport rate (ETR) was almost a 20 percent higher in plants at [CO2]enr regardless drought endured by seedlings. The ETR/Anet was lower under [CO2]enr, pointing to a high capacity to maintain sinks for the uptake of extra carbon in the atmosphere. Impact of drought on the leaf metabolome, as a whole, was more evident than that from [CO2] enrichment of the atmosphere. Changes in pool of non-structural carbohydrates were observed mainly as a consequence of water deficit including increases of fructose, glucose, and proto-quercitol. Most of the metabolites affected by drought back up to levels of non-stressed seedlings after rewetting (recovery phase). It can be concluded that carbon uptake was stimulated by [CO2]enr, even under the stomatal closure that accompanied moderate drought. In the last, there was a positive effect in intrinsic water use efficiency (WUEi), which was much more improved under [CO2]enr. Leaf metabolome was little responsible and some few metabolites changed mainly in response to drought, with little differences between [CO2] growth conditions.

Phenolic and volatile compounds in Quercus humboldtii Bonpl. wood: effect of toasting with respect to oaks traditionally used in cooperage.

BACKGROUND: The most frequent renewal of barrels of different origins and species is a current trend, but this demand does not match the current availability of wood. An alternative could be the use of Quercus humboldtii wood. However, there is little information about its composition. Because of this, the aim was to study low-molecular-weight phenols (LMWP), ellagitannins and volatile compounds in untoasted and toasted Q. humboldtii oak, and compare these with the species traditionally used in cooperage: Q. petraea (French and Romanian) and Q. alba (American). RESULTS: The LMWPs in Q. humboldtii were comparable to those in Q. petraea and Q. alba. Ellagitannin composition in Q. humboldtii was similar to that in Q. alba. The toasting process improved volatile composition, mainly in Q. humboldtii, presenting the highest concentration of several volatile compounds. CONCLUSION: The results indicate that Q. humboldtii could be considered suitable for aging wine, although it is necessary to continue the study of this wood species to confirm its potential use in oenology. © 2018 Society of Chemical Industry.

Metabolic response to elevated CO2 levels in Pinus pinaster Aiton needles in an ontogenetic and genotypic-dependent way.

Global climate changes involve elevated atmospheric [CO2], fostering the carbon allocation to tree sink tissues, partitioning it into metabolic pathways. We use metabolomics analysis in adult and juvenile needles of four Pinus pinaster genotypes exposed to two levels of growth [CO2]: ambient (400 µmol mol-1) and enriched (800 µmol mol-1), to know if the metabolic responses are genotype-dependent and vary according to the stage of needle ontogeny. The eCO2-induced changes in the needle metabolomes are more significant in secondary metabolism pathways and especially meaningful in juvenile needles. The heteroblasty has important consequences in the expression of the metabolome, and on the plasticity to CO2, determining the level of specific metabolite accumulation, showing an interdependence between adult and juvenile needles. The P. pinaster needle metabolomes also show clear quantitative differences linked to genotype, as well as regarding the metabolic response to eCO2, showing both, common and genotype-specific biochemical responses. Thus, the changes in flavonol levels are mainly genotype-independent, while those in terpenoid and free fatty acids are mainly genotype-dependent, ratifying the importance of genotype to determine the metabolic response to eCO2. To understand the adaptation mechanisms that tree species can develop to cope with eCO2 it is necessary to know the genetically distinct responses within a species to recognize the CO2-induced changes from the divergent approaches, what can facilitate knowing also the possible interrelation of the physiological and metabolic responses. That could explain the controversial effects of eCO2 on the carbon-based metabolite in conifers, at the inter- and intra-specific level.

Organ-specific metabolic responses to drought in Pinus pinaster Ait.

Drought is an important driver of plant survival, growth, and distribution. Water deficit affects different pathways of metabolism, depending on plant organ. While previous studies have mainly focused on the metabolic drought response of a single organ, analysis of metabolic differences between organs is essential to achieve an integrated understanding of the whole plant response. In this work, untargeted metabolic profiling was used to examine the response of roots, stems, adult and juvenile needles from Pinus pinaster Ait. full-sib individuals, subjected to a moderate and long lasting drought period. Cyclitols content showed a significant alteration, in response to drought in all organs examined, but other metabolites increased or decreased differentially depending on the analyzed organ. While a high number of flavonoids were only detected in aerial organs, an induction of the glutathione pathway was mainly detected in roots. This result may reflect different antioxidant mechanisms activated in aerial organs and roots. Metabolic changes were more remarkable in roots than in the other organs, highlighting its prominent role in the response to water stress. Significant changes in flavonoids and ascorbate metabolism were also observed between adult and juvenile needles, consistent with previously proven differential functional responses between the two developmental stages. Genetic polymorphisms in candidate genes coding for a Myb1 transcription factor and a malate dehydrogenase (EC 1.1.1.37) were associated with different concentration of phenylalanine, phenylpropanoids and malate, respectively. The results obtained will support further research on metabolites and genes potentially involved in functional mechanisms related to drought tolerance in trees.

Wood impregnation of yeast lees for winemaking.

This study develops a new method to produce more complex wines by means of an indirect diffusion of wood aromas from yeast cell-walls. An exogenous lyophilized biomass was macerated with an ethanol wood extract solution and subsequently dried. Different times were used for the adsorption of polyphenols and volatile compounds to the yeast cell-walls. The analysis of polyphenols and volatile compounds (by HPLC/DAD and GC-MS, respectively) demonstrate that the adsorption/diffusion of these compounds from the wood to the yeast takes place. Red wines were also aged with Saccharomyces cerevisiae lees that had been impregnated with wood aromas and subsequently dried. Four different types of wood were used: chestnut, cherry, acacia and oak. Large differences were observed between the woods studied with regards to their volatile and polyphenolic profiles. Sensory evaluations confirmed large differences even with short-term contact between the wines and the lees, showing that the method could be of interest for red wine making. In addition, the results demonstrate the potential of using woods other than oak in cooperage.

Non-targeted metabolomic profile of Fagus sylvatica L. leaves using liquid chromatography with mass spectrometry and gas chromatography with mass spectrometry.

INTRODUCTION: Fagus sylvatica L. is one of the most widely distributed broad-leaved tree species in central and western Europe, important to the forest sector and an accurate biomarker of climate change. OBJECTIVE: To profile the beech leaf metabolome for future studies in order to investigate deeper into the characterisation of its metabolic response. METHODS: Leaf extracts were analysed using LC-MS by electrospray ionisation in negative mode from m/z 100-1700 and GC-MS by electron ionisation in scan mode from m/z 35-800. RESULTS: The LC-MS profile resulted in 56 compounds, of which 43 were identified and/or structurally characterised, including hydroxycinnamic acid derivatives, flavan-3-ols and proanthocyanidins, and flavonols. From a second analysis based on GC-MS, a total of 111 compounds were identified, including carbohydrates, polyalcohols, amino acids, organic acids, fatty acids, phenolic compounds, terpenoids, sterols and other related compounds. Many of the compounds identified were primary metabolites involved in major plant metabolic pathways, however, some secondary metabolites were also detected. Some of them play roles as tolerance-response osmoregulators and osmoprotectors in abiotic stress, or as anti-oxidants that reduce the effect of reactive oxygen species and promote many protective functions in plants. CONCLUSIONS: This study provides a broad and relevant insight into the metabolic status of F. sylvatica leaves, and serves as a base for future studies on physiological and molecular mechanisms involved in biotic or abiotic stress.

Nontargeted GC-MS approach for volatile profile of toasting in cherry, chestnut, false acacia, and ash wood.

By using a nontargeted GC-MS approach, 153 individual volatile compounds were found in extracts from untoasted, light toasted and medium-toasted cherry, chestnut, false acacia, as well as European and American ash wood, used in cooperage for aging wines, spirits and other beverages. In all wood types, the toasting provoked a progressive increase in carbohydrate derivatives, lactones and lignin constituents, along with a variety of other components, thus increasing the quantitative differences among species with the toasting intensity. The qualitative differences in the volatile profiles allow for identifying woods from cherry (being p-anisylalcohol, p-anisylaldehyde, p-anisylacetone, methyl benzoate and benzyl salicylate detected only in this wood), chestnut (cis and trans whisky lactone) and false acacia (resorcinol, 3,4-dimethoxyphenol, 2,4-dihydroxy benzaldehyde, 2,4-dihydroxyacetophenone, 2,4-dihydroxypropiophenone and 2,4-dihydroxy-3-methoxyacetophenone), but not those from ash, because of the fact that all compounds present in this wood are detected in at least one other. However, the quantitative differences can be clearly used to identify toasted ash wood, with tyrosol being most prominent, but 2-furanmethanol, 3- and 4-ethylcyclotene, α-methylcrotonolactone, solerone, catechol, 3-methylcatechol and 3-hydroxybenzaldehyde as well. Regarding oak wood, its qualitative volatile profile could be enough to distinguish it from cherry and acacia woods, and the quantitative differences from chestnut (vanillyl ethyl ether, isoacetovanillone, butirovanillone, 1-(5-methyl-2-furyl)-2-propanone and 4-hydroxy-5,6-dihydro-(2H)-pyran-2-one) and ash toasted woods.

LC-DAD/ESI-MS/MS study of phenolic compounds in ash (Fraxinus excelsior L. and F. americana L.) heartwood. Effect of toasting intensity at cooperage.

The phenolic composition of heartwood extracts from Fraxinus excelsior L. and F. americana L., both before and after toasting in cooperage, was studied using LC-DAD/ESI-MS/MS. Low-molecular weight (LMW) phenolic compounds, secoiridoids, phenylethanoid glycosides, dilignols and oligolignols compounds were detected, and 48 were identified, or tentatively characterized, on the basis of their retention time, UV/Vis and MS spectra, and MS fragmentation patterns. Some LMW phenolic compounds like protocatechuic acid and aldehyde, hydroxytyrosol and tyrosol, were unlike to those for oak wood, while ellagic and gallic acid were not found. The toasting of wood resulted in a progressive increase in lignin degradation products with regard to toasting intensity. The levels of some of these compounds in medium-toasted ash woods were much higher than those normally detected in toasted oak, highlighting vanillin levels, thus a more pronounced vanilla character can be expected when using toasted ash wood in the aging wines. Moreover, in seasoned wood, we found a great variety of phenolic compounds which had not been found in oak wood, especially oleuropein, ligstroside and olivil, along with verbascoside and isoverbascoside in F. excelsior, and oleoside in F. americana. Toasting mainly provoked their degradation, thus in medium-toasted wood, only four of them were detected. This resulted in a minor differentiation between toasted ash and oak woods. The absence of tannins in ash wood, which are very important in oak wood, is another peculiar characteristic that should be taken into account when considering its use in cooperage.

Polyphenolic profile as a useful tool to identify the wood used in wine aging.

Although oak wood is the main material used in cooperage, other species are being considered as possible sources of wood for the production of wines and their derived products. In this work we have compared the phenolic composition of acacia (Robinia pseudoacacia), chestnut (Castanea sativa), cherry (Prunus avium) and ash (Fraxinus excelsior and F. americana) heartwoods, by using HPLC-DAD/ESI-MS/MS (some of these data have been showed in previous paper), as well as the changes that toasting intensity at cooperage produce in each polyphenolic profile. Before toasting, each wood shows a different and specific polyphenolic profile, with both qualitative and quantitative differences among them. Toasting notably changed these profiles, in general, proportionally to toasting intensity and led to a minor differentiation among species in toasted woods, although we also found phenolic markers in toasted woods. Thus, methyl syringate, benzoic acid, methyl vanillate, p-hydroxybenzoic acid, 3,4,5-trimethylphenol and p-coumaric acid, condensed tannins of the procyanidin type, and the flavonoids naringenin, aromadendrin, isosakuranetin and taxifolin will be a good tool to identify cherry wood. In acacia wood the chemical markers will be the aldehydes gallic and ß-resorcylic and two not fully identified hydroxycinnamic compounds, condensed tannins of the prorobinetin type, and when using untoasted wood, dihydrorobinetin, and in toasted acacia wood, robinetin. In untoasted ash wood, the presence of secoiridoids, phenylethanoid glycosides, or di and oligolignols will be a good tool, especially oleuropein, ligstroside and olivil, together verbascoside and isoverbascoside in F. excelsior, and oleoside in F. americana. In toasted ash wood, tyrosol, syringaresinol, cyclolovil, verbascoside and olivil, could be used to identify the botanical origin. In addition, in ash wood, seasoned and toasted, neither hydrolysable nor condensed tannins were detected. Lastly, in chestnut wood, gallic and ellagic acids and hydrolysable tannins of both the gallotannin and ellagitannin type, can be used as chemical markers.

Polyphenols in red wine aged in acacia (Robinia pseudoacacia) and oak (Quercus petraea) wood barrels.

Polyphenolic composition of two Syrah wines aged during 6 or 12 months in medium toasting acacia and oak 225L barrels was studied by LC-DAD-ESI/MS. A total of 43 nonanthocyanic phenolic compounds were found in all wines, and other 15 compounds only in the wines from acacia barrels. Thus, the nonanthocyanic phenolic profile could be a useful tool to identify the wines aged in acacia barrels. Among all of them the dihydrorobinetin highlights because of its high levels, but also robinetin, 2,4-dihydroxybenzaldehyde, a tetrahydroxydihydroflavonol, fustin, butin, a trihydroxymethoxydihydroflavonol and 2,4-dihydroxybenzoic acid were detected at appreciable levels in wines during aging in acacia barrels, and could be used as phenolic markers for authenticity purposes. Although longer contact time with acacia wood mean higher concentrations of phenolic markers found in wines, the identification of these wines will also be easy after short aging times due the high levels reached by these compounds, even after only 2 months of aging.

Effect of toasting intensity at cooperage on phenolic compounds in acacia (Robinia pseudoacacia) heartwood.

The phenolic composition of heartwood from Robinia pseudoacacia, commonly known as false acacia, before and after toasting in cooperage was studied by HPLC-DAD and HPLC-DAD/ESI-MS/MS. A total of 41 flavonoid and nonflavonoid compounds were identified, some tentatively, and quantified. Seasoned acacia wood showed high concentrations of flavonoid and low levels of nonflavonoid compounds, the main compounds being the dihydroflavonols dihydrorobinetin, fustin, tetrahydroxy, and trihydroxymethoxy dihydroflavonol, the flavonol robinetin, the flavanones robtin and butin, and a leucorobinetinidin, none of which are found in oak wood. The low molecular weight (LMW) phenolic compounds present also differed from those found in oak, since compounds with a ß-resorcylic structure, gallic related compounds, protocatechuic aldehyde, and some hydroxycinnamic compounds are included, but only a little gallic and ellagic acid. Toasting changed the chromatographic profiles of extracts spectacularly. Thus, the toasted acacia wood contributed flavonoids and condensed tannins (prorobinetin type) in inverse proportion to toasting intensity, while LMW phenolic compounds were directly proportional to toasting intensity, except for gallic and ellagic acid and related compounds. Even though toasting reduced differences between oak and acacia, particular characteristics of this wood must be taken into account when considering its use in cooperage: the presence of flavonoids and compounds with ß-resorcylic structure and the absence of hydrolyzable tannins.

Characterization of volatile constituents in commercial oak wood chips.

The volatile composition of the different oak wood pieces (chips of Quercus spp.) that can be found on the market to be used as alternatives to barrels for aging wines, as well as of chips of Quercus pyrenaica which are being introduced, was studied, evaluating the contents of volatile phenols, lactones, furanic compounds, pyranones, phenolic aldehydes, phenolic ketones, and others. In regard to the overall results, the volatile composition of these products varies widely and has not been clearly laid out according to either the oak species or the wood toasting intensity. Taking into account that the different characteristics of alternatives to barrel products are reflected in the wine treated with them and that an oenological profile based on these variables (origin and toasting level) cannot be defined, only an appropriate chemical analysis would reveal the quality of alternative-to-barrel products and allow us to attempt to foresee its effects on the chemical and organoleptic characteristics of the wines treated with them. On the other hand, the Q. pyrenaica alternative products are very similar to those of other species, with some aromatic particularities, such as their high levels of furanic compounds, eugenol, Furaneol, and cis-whiskylactone, and low levels of vanillin.

Phenolic compounds in chestnut (Castanea sativa Mill.) heartwood. Effect of toasting at cooperage.

The phenolic and tannic composition of heartwood extracts from Castanea sativa Mill., before and after toasting in cooperage, were studied using HPLC-DAD and HPLC-DAD/ESI-MS, and some low molecular weight phenolic compounds and hydrolyzable tannins were found. The low molecular weight phenolic compounds were lignin constituents as the acids gallic, protocatechuic, vanillic, syringic, ferulic, and ellagic, the aldehydes protocatechuic, vanillic, syringic, coniferylic, and sinapic, and the coumarin scopoletin. Their patterns were somewhat different those of oak because oak does not contain compounds such protocatechuic acid and aldehyde and is composed of much lower amounts of gallic acid than chestnut. Vescalagin and castalagin were the main ellagitannins, and acutissimin was tentatively identified for the first time in this wood. Moreover, some gallotannins were tentatively identified, including different isomers of di, tri, tetra, and pentagalloyl glucopyranose, and di and trigalloyl-hexahydroxydiphenoyl glucopyranose, comprising 20 different compounds, as well as some ellagic derivatives such as ellagic acid deoxyhexose, ellagic acid dimer dehydrated, and valoneic acid dilactone. These ellagic derivatives as well as some galloyl and hexahydroxydiphenoyl derivatives were tentatively identified for the first time in this wood. The profile of tannins was therefore different from that of oak wood because oak only contains tannins of the ellagitannins type. Seasoned and toasted chestnut wood showed a very different balance between lignin derivatives and tannins because toasting resulted in the degradation of tannins and the formation of low molecular weight phenolic compounds from lignin degradation. Moreover, the different toasting levels provoked different balances between tannins and lignin constituents because the intensity of lignin and tannin degradation was in relation to the intensity of toasting.

Phenolic compounds in cherry ( Prunus avium ) heartwood with a view to their use in cooperage.

The phenolic and tannic composition of heartwood extracts from Prunus avium , commonly known as cherry tree, before and after toasting in cooperage were studied using HPLC-DAD and HPLC-DAD/ESI-MS. Nonflavonoid (16 compounds) and flavonoid (27 compounds) polyphenols were identified, 12 of them in only a tentative way. The nonflavonoids found were lignin constituents, and their pattern is different compared to oak, since they include compounds such as protocatechuic acid and aldehyde, p-coumaric acid, methyl vanillate, methyl syringate, and benzoic acid, but not ellagic acid, and only a small quantity of gallic acid. In seasoned wood we found a great variety of flavonoid compounds which have not been found in oak wood for cooperage, mainly, in addition to the flavan-3-ols (+)-catechin, a B-type procyanidin dimer, and a B-type procyanidin trimer, the flavanones naringenin, isosakuranetin, and eriodictyol and the flavanonols aromadendrin and taxifolin. Seasoned and toasted cherry wood showed different ratios of flavonoid to nonflavonoid compounds, since toasting results in the degradation of flavonoids, and the formation of nonflavonoids from lignin degradation. On the other hand, the absence of hydrolyzable tannins in cherry wood, which are very important in oak wood, is another particular characteristic of this wood that should be taken into account when considering its use in cooperage.

Micro-oxygenation strategy depends on origin and size of oak chips or staves during accelerated red wine aging.

The practice of wine aging in stainless steel tank involves storing wine in contact with wood and dosing it with small oxygen quantities in order to obtain a final wine more stable in time and with the same characteristics of barrel-aged wines. Oxygen dosing is a key factor and, to achieve a correct development of wine, needs to be applied according to wine necessities and to the kind of wood chosen. This paper shows the results obtained from the study of oxygen required by a same wine aged in tanks with different alternative products (chips and staves) made of American (Q. alba), French (Q. petraea) and Spanish oak (Q. pyrenaica), with a strategy of micro-oxygenation as required. The results indicate that the size and origin of the wood used determine the oxygen management during the process. In fact, wine treated with big pieces (staves) consumes more oxygen and, with regard to wood origin, wine aged with French oak (Q. petraea) products needs of a higher oxygen dosage.

Volatile compounds in acacia, chestnut, cherry, ash, and oak woods, with a view to their use in cooperage.

Extracts of wood from acacia, European ash, American ash, chestnut, cherry, and three oak species (Quercus pyrenaica, Quercus alba and Quercus petraea) before and after toasting in cooperage were studied by GC-MS. 110 compounds were detected, and 97 of them were identified. In general, all studied woods showed more lignin derivatives than lipid and carbohydrate derivatives, with a higher variety of compounds detected and abundance of them. The toasting led to an increase in the concentrations of most of these compounds, and this increase is especially important in acacia, chestnut and ash woods. The cis and trans isomers of beta-methyl-gamma-octalactone and isobutyrovanillone were only detected in oak wood, 3,4-dimethoxyphenol and 2,4-dihydroxybenzaldehyde only in acacia wood, and p-anisaldehyde and benzylsalicylate only in cherry wood, before and after toasting, and these compounds could be considered chemical markers for each one of these woods. Moreover, each wood has a characteristic volatile composition, from a quantitative point of view, and therefore we can expect a characteristic sensorial profile. The oak wood turned out to be the most balanced, since although it provides a lot of volatile compounds to the aroma and flavor of aged wine, it can do so without masking their primary and secondary aroma. On the whole, toasted acacia and chestnut woods showed a very high richness of studied compounds, as lignin as lipid and carbohydrate derivatives, while cherry and ash were much richer than toasted oak wood in lignin derivatives, but much poorer in lipid and carbohydrate derivatives.

Volatile compounds and sensorial characterization of wines from four Spanish denominations of origin, aged in Spanish Rebollo (Quercus pyrenaica Willd.) oak wood barrels.

The evolution of almost 40 oak-related volatile compounds and the sensorial characteristics of red wines from four Spanish denominations of origin (DOs) (Bierzo, Toro, Ribera de Duero, and Rioja) during aging in barrels made of Rebollo oak wood, Quercus pyrenaica, were studied and compared to the same wines aged in American and French oak barrels. Each oak wood added unique and special characteristics to the wine, and in addition, each wine showed a different ability to extract the compounds, which result in these characteristics from the oak wood. In general, wines aged in Q. pyrenaica wood were characterized by high levels of eugenol, guaiacol, and other volatile phenols. In regards to compounds like cis-whiskylactone or maltol, the behavior of this wood is very similar to that of American oaks. When considering phenolic aldehydes and ketones, the levels of these compounds are intermediate between those of French and American woods and depend greatly on the type of wine. The type of oak, on the other hand, does not affect the chromatic characteristics of the wines. In sensory analysis, the biggest differences are found in the olfactory phase. Among the four DOs studied, wine aged in Q. pyrenaica presented the highest notes of wood, with more aromas of roasting, toasting, milky coffee, spices, or wine-wood interactions. The wines aged in barrels made of Q. pyrenaica wood were highly regarded, and preference was shown for them over those same wines when they had been aged in barrels of American or French oak.