Demonstration of pectic polysaccharides in cork cell wall from Quercus suber L

Migration of Tannins and Pectic Polysaccharides from Natural Cork Stoppers to the Hydroalcoholic Solution

Ellagitannins, condensed tannins, and pectic-derived polysaccharides were removed from natural cork stoppers using hydroalcoholic solution. Two main populations of migrated compounds were determined; the major one with molecular weight (MW) between 0.2 and 1 kDa and the second with 2.1 kDa and polydispersity of 1.3. Two residual populations mainly composed of condensed tannins were also observed between 2.5 and 4.5 kDa and higher than 15 kDa. Simple, C-glycosidic, complex, and oligomeric ellagitannins were identified by high-performance liquid chromatography-diode array detection/electrospray ionization-mass spectrometry (HPLC-DAD/ESI-MS). Ellagitannins linked to condensed tannins and some pectic-derived polysaccharides were also tentatively identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF-MS). This preliminary work opens an opportunity for the cork stoppers industry due to the relevance of this type of compounds on the astringency and bitterness of wines.

Musty and Moldy Taint in Wines: A Review

The literature about musty and moldy taint—the so-called cork taint—in wines is varied because there are many different molecules involved in this wine defect. Chloroanisoles are the most relevant compound responsible for cork taint and of these, 2,4,6-trichloroanisole (TCA) is the most common, but 2,3,4,6-tetrachloroanisole (TeCA) and 2,4,6-tribromoanisole (TBA) can also be responsible of this defect. For other compounds involved in cork taint, geosmin and 2-methylisoborneol (2-MIB) are responsible for earthy off-flavor; pyrazines cause vegetable odors, and guaiacol results in smoked, phenolic and medicinal defects. Off-odors of mushroom in wines are caused by 1-octen-3-ol and 1-octen-3-one coming from grapes contaminated by bunch rot (Botrytis cinerea). The sensory aspects of these molecules are illustrated in this review. Generally, the most important cause of this wine contamination is the natural cork of bottle stoppers, but this is not always true. Different origins of contamination include air pollution of the cellars, wood materials, barrels and chips. A review of the possible prevention or remedial treatments to cork taint is also presented. The best solution for this off-flavor is to prevent the wine contaminations.

Finding Value in Wastewaters from the Cork Industry: Carbon Dots Synthesis and Fluorescence for Hemeprotein Detection

Valorisation of industrial low-value waste residues was preconized. Hence, carbon dots (C-dots) were synthesized from wastewaters of the cork industry-an abundant and affordable, but environmentally-problematic industrial effluent. The carbon nanomaterials were structurally and morphologically characterised, and their photophysical properties were analysed by an ensemble of spectroscopy techniques. Afterwards, they were successfully applied as highly-sensitive fluorescence probes for the direct detection of haemproteins. Haemoglobin, cytochrome c and myoglobin were selected as specific targets owing to their relevant roles in living organisms, wherein their deficiencies or surpluses are associated with several medical conditions. For all of them, remarkable responses were achieved, allowing their detection at nanomolar levels. Steady-state and time-resolved fluorescence, ground-state UV-Vis absorption and electronic circular dichroism techniques were used to investigate the probable mechanisms behind the fluorescence turn-off of C-dots. Extensive experimental evidence points to a static quenching mechanism. Likewise, resonance energy transfer and collisional quenching have been discarded as excited-state deactivating mechanisms. It was additionally found that an oxidative, photoinduced electron transfer occurs for cytochrome c, the most electron-deficient protein. Besides, C-dots prepared from citric acid/ethylenediamine were comparatively assayed for protein detection and the differences between the two types of nanomaterials highlighted.

Growth Region Impacts Cell Wall Properties and Hard-to-Cook Phenotype of Canned Navy Beans (Phaseolus vulgaris)

Cellular mechanisms underpinning the hard-to-cook phenomenon are poorly understood. Navy beans (Phaseolus vulgaris) from the same cultivar but grown in different regions of North America showed different canning characteristics. Up to 46.4% more force was required to disrupt hard beans (HB) grown in Ontario compared with soft beans (SB) grown in Manitoba. HB absorbed 12.5% and 14.7% less water during blanching and canning, respectively. Microscopic assessment revealed that canning led to swelling of middle lamella and cell walls, but preservation of cell adhesion in both types of beans. Immunofluorescence microscopy showed reduced labelling of methyl-esterified homogalacturonan (HG) and more non-methyl-esterified HG and arabinan epitopes in HB. Compositional analysis indicated that the polysaccharides from HB were less water soluble and enriched in neutral sugars, including 46.5% more arabinose and 51.8% more galactose than in SB. ELISA analysis of polymers in the canning medium supported the increased solubility of cell wall polymers in SB. In the same cultivar, growth region affects cell wall properties with consequences for processing, eating and nutritional quality.

Structure and Properties of Cork-Silica Xerogel Nanocomposites: Influence of the Cork Content

Environmentally friendly nanocomposites were synthesized from a silica precursor and cork under mild conditions and dried at atmospheric pressure. Because of the covalent bonding between the components, these CorSil nanocomposites are homogeneous, light (apparent density in the range 360-750 kg m^-3), machinable, with the Shore D hardness up to 67 and compressive strength up to 22.6 MPa. These properties place them as good replacements for wood, other natural products, and thermoplastic polymers, with the advantage of being flame-retardant. The influence of the cork content and grain size on the structure, porosity, and mechanical properties of the nanocomposites was studied using infrared spectroscopy, sorption isotherms, compressive strength, and Shore D hardness measurements.

Investigating Aspergillus nidulans secretome during colonisation of cork cell walls

Cork, the outer bark of Quercus suber, shows a unique compositional structure, a set of remarkable properties, including high recalcitrance. Cork colonisation by Ascomycota remains largely overlooked. Herein, Aspergillus nidulans secretome on cork was analysed (2DE). Proteomic data were further complemented by microscopic (SEM) and spectroscopic (ATR-FTIR) evaluation of the colonised substrate and by targeted analysis of lignin degradation compounds (UPLC-HRMS). Data showed that the fungus formed an intricate network of hyphae around the cork cell walls, which enabled polysaccharides and lignin superficial degradation, but probably not of suberin. The degradation of polysaccharides was suggested by the identification of few polysaccharide degrading enzymes (β-glucosidases and endo-1,5-α-l-arabinosidase). Lignin degradation, which likely evolved throughout a Fenton-like mechanism relying on the activity of alcohol oxidases, was supported by the identification of small aromatic compounds (e.g. cinnamic acid and veratrylaldehyde) and of several putative high molecular weight lignin degradation products. In addition, cork recalcitrance was corroborated by the identification of several protein species which are associated with autolysis. Finally, stringent comparative proteomics revealed that A. nidulans colonisation of cork and wood share a common set of enzymatic mechanisms. However the higher polysaccharide accessibility in cork might explain the increase of β-glucosidase in cork secretome.

BIOLOGICAL SIGNIFICANCE

Cork degradation by fungi remains largely overlook. Herein we aimed at understanding how A. nidulans colonise cork cell walls and how this relates to wood colonisation. To address this, the protein species consistently present in the secretome were analysed, as well as major alterations occurring in the substrate, including lignin degradation compounds being released. The obtained data demonstrate that this fungus has superficially attacked the cork cell walls apparently by using both enzymatic and Fenton-like reactions. Only a few polysaccharide degrading enzymes could be detected in the secretome which was dominated by protein species associated with autolysis. Lignin degradation was corroborated by the identification of some degradation products, but the suberin barrier in the cell wall remained virtually intact. Comparative proteomics revealed that cork and wood colonisation share a common set of enzymatic mechanisms.

Changes in pectins and MAPKs related to cell development during early microspore embryogenesis in Quercus suber L

The occurrence and significance of changes in cell wall components and signalling molecules has been investigated during early microspore embryogenesis in cork oak (Quercus suber L.) in relation to cell proliferation and cell differentiation. Microspore embryogenesis has been induced in in vitro anther cultures of Q. suber by the application of a stress treatment of 33 degrees C. After the treatment, microspores at the responsive developmental stage of vacuolate microspore switched towards proliferation and the embryogenesis pathway to further produce haploid plantlets. Ultrastructural and immunocytochemical analysis revealed changes in cell organisation after induction at different developmental stages, the cellular features displayed being in relation to the activation of proliferative activity and the beginning of differentiation in young and late proembryos. Immunogold labelling with JIM5 and JIM7 antibodies showed a different presence of pectin and level of its esterification in cell walls at different developmental stages. Non-esterified pectins were found in higher proportions in cells of late proembryos, suggesting that pectin de-esterification could be related to the beginning of differentiation. The presence and subcellular distribution of Erk 1/2 MAPK homologues have been investigated by immunoblotting, immunofluorescence and immunogold labelling. The results showed an increase in the expression of these proteins with a high presence in the nucleus, during early microspore proembryos development. The reported changes during early microspore embryogenesis are modulated in relation to proliferation and differentiation events. These findings provided new evidences for a role of MAPK signalling pathways in early microspore embryogenesis, specifically in proliferation, and would confer information for the cell fate and the direction of the cell development.