Retention of Proanthocyanidin in Wine-like Solution Is Conferred by a Dynamic Interaction between Soluble and Insoluble Grape Cell Wall Components

For better understanding of the factors that impact proanthocyanidin (PA) adsorption by insoluble cell walls or interaction with soluble cell wall-derived components, application of a commercial polygalacturonase enzyme preparation was investigated to modify grape cell wall structure. Soluble and insoluble cell wall material was isolated from the skin and mesocarp components of <i>Vitis vinifera</i> Shiraz grapes. It was observed that significant depolymerization of the insoluble grape cell wall occurred following enzyme application to both grape cell wall fractions, with increased solubilization of rhamnogalacturonan-enriched, low molecular weight polysaccharides. However, in the case of grape mesocarp, the solubilization of protein from cell walls (in buffer) was significant and increased only slightly by the enzyme treatment. Enzyme treatment significantly reduced the adsorption of PA by insoluble cell walls, but this effect was observed only when material solubilized from grape cell walls had been removed. The loss of PA through interaction with the soluble cell wall fraction was observed to be greater for mesocarp than skin cell walls. Subsequent experiments on the soluble mesocarp cell wall fraction confirmed a role for protein in the precipitation of PA. This identified a potential mechanism by which extracted grape PA may be lost from wine during vinification, as a precipitate with solubilized grape mesocarp proteins. Although protein was a minor component in terms of total concentration, losses of PA via precipitation with proteins were in the order of 50% of available PA. PA-induced precipitation could proceed until all protein was removed from solution and may account for the very low levels of residual protein observed in red wines. The results point to a dynamic interaction of grape insoluble and soluble components in modulating PA retention in wine

Factors Affecting Skin Tannin Extractability in Ripening Grapes

The acetone-extractable (70% v/v) skin tannin content of Vitis vinifera L. cv. Cabernet Sauvignon grapes was found to increase during late-stage ripening. Conversely, skin tannin content determined following ethanol extraction (10, 20, and 50% v/v) did not consistently reflect this trend. The results indicated that a fraction of tannin became less extractable in aqueous ethanol during ripening. Skin cell walls were observed to become more porous during ripening, which may facilitate the sequestering of tannin as an adsorbed fraction within cell walls. For ethanol extracts, tannin molecular mass increased with advancing ripeness, even when extractable tannin content was constant, but this effect was negligible in acetone extracts. Reconstitution experiments with isolated skin tannin and cell wall material indicated that the selectivity of tannin adsorption by cell walls changed as tannin concentration increased. Tannin concentration, tannin molecular mass, and cell wall porosity are discussed as factors that may influence skin tannin extractability

Survey of the Variation in Grape Marc Condensed Tannin Composition and Concentration and Analysis of Key Compositional Factors

Grape marc contains a number of compounds with potential antimethanogenic activity in ruminants, including condensed tannins (CTs). Using direct phloroglucinolysis, a survey of CT chemistry across 66 grape marc samples showed diversity in concentration (6.9 to 138.8 g/kg of dry matter). Concentration was found to be independent of CT composition, although all compositional variables were significantly correlated (<i>P</i> < 0.0001). Twenty samples diverse in CT were selected from a cluster analysis and analyzed for compounds relevant to ruminant digestion and methanogenesis, including metabolizable energy (6.6–12.0 MJ/kg DM), crude protein (3.2–14.4% DM), neutral detergent fiber (18.4–61.4% DM), and ethanol soluble carbohydrates (2.0–40.6% DM). Fatty acid concentrations varied throughout the 20 samples (5.2–184.5 g/kg DM), although fatty acid profile showed two distinct groups. Grape marc varies widely in nutritional value, and in compounds that have been linked with changes in ruminant digestion and methane emissions

Kinetics and Cure Mechanism in Aromatic Polybenzoxazines Modified Using Thermoplastic Oligomers and Telechelics

A series of blends is prepared comprising 2,2-bis­(3,4-dihydro-3-phenyl-2<i>H</i>-1,3-benzoxazine)­propane (BA-a) with variously 5, 10, or 20 wt % of a selected oligomer represented by poly­(arylsulfone) (PSU) or poly­(arylethersulfone) (PES). The oligomers, comprising either chloro-, hydroxyl- or benzoxazinyl- (Bz) terminal functionality, are of low molecular weight (3000–12000 g mol^–1). The introduction of the oligomers is shown to initiate the polymerization of a bisbenzoxazine monomer where the terminal functionality of the oligomer is coreactive (e.g., hydroxyl or benzoxazine) without having a detrimental effect on the polymerization kinetics (similar values for the activation energy and orders of reaction are obtained). The introduction of the nonreactive chloro-terminated oligomer appears to favor the formation of an interpenetrating network (IPN) with a higher energy of activation. The thermal stability of the blends is generally increased compared with the polybenzoxazine homopolymer, regardless of the molecular weight or thermoplastic loading. Aside from the aforementioned PSU_Cl-containing IPN, the nature of the resulting network is slightly modified by the addition of the thermoplastic with similar or slightly elevated cross-link densities recorded (compared with the polybenzoxazine homopolymer). The heterogeneity of the network increases with a broadening of the tan δ response, suggesting an improvement in the toughness of the resulting blend

Examining the Initiation of the Polymerization Mechanism and Network Development in Aromatic Polybenzoxazines

Three bis-benzoxazine monomers based on the aniline derivatives of bisphenol A (BA-a), bisphenol F (BF-a), and 3,3′-thiodiphenol (BT-a) are examined using a variety of spectroscopic, chromatographic, and thermomechanical techniques. The effect on the polymerization of the monomers is compared using two common compounds, 3,3′-thiodiphenol (TDP) and 3,3′-thiodipropionic acid (TDA), at a variety of loadings. It is found that the diacid has a greater effect on reducing the onset of polymerization and increasing cross-link density and <i>T</i>_g for a given benzoxazine. However, the addition of >5 wt % of the diacid had a detrimental effect on the cross-link density, <i>T</i>_g, and thermal stability of the polymer. The kinetics of the polymerization of BA-a were found to be well described using an autocatalytic model for which values of <i>n</i> = 1.64 and <i>m</i> = 2.31 were obtained for the early and later stages of reaction (activation energy = 81 kJ/mol). Following recrystallization the same monomer yielded values <i>n</i> = 1.89, <i>m</i> = 0.89, and <i>E</i>_a = 94 kJ/mol (confirming the influence of higher oligomers on reactivity). The choice of additive (in particular the magnitude of its p<i>K</i>_a) appears to influence the nature of the network formation from a linear toward a more clusterlike growth mechanism

Measuring the Molecular Dimensions of Wine Tannins: Comparison of Small-Angle X‑ray Scattering, Gel-Permeation Chromatography and Mean Degree of Polymerization

The molecular size of wine tannins can influence astringency, and yet it has been unclear as to whether the standard methods for determining average tannin molecular weight (MW), including gel-permeation chromatography (GPC) and depolymerization reactions, are actually related to the size of the tannin in wine-like conditions. Small-angle X-ray scattering (SAXS) was therefore used to determine the molecular sizes and corresponding MWs of wine tannin samples from 3 and 7 year old Cabernet Sauvignon wine in a variety of wine-like matrixes: 5–15% and 100% ethanol; 0–200 mM NaCl and pH 3.0–4.0, and compared to those measured using the standard methods. The SAXS results indicated that the tannin samples from the older wine were larger than those of the younger wine and that wine composition did not greatly impact on tannin molecular size. The average tannin MWs as determined by GPC correlated strongly with the SAXS results, suggesting that this method does give a good indication of tannin molecular size in wine-like conditions. The MW as determined from the depolymerization reactions did not correlate as strongly with the SAXS results. To our knowledge, SAXS measurements have not previously been attempted for wine tannins

Comparison of Extraction Protocols To Determine Differences in Wine-Extractable Tannin and Anthocyanin in <i>Vitis vinifera</i> L. cv. Shiraz and Cabernet Sauvignon Grapes

Cabernet Sauvignon and Shiraz grapes were sourced from different regions within Australia, and microvinified with a skin contact period of 6 days. Grape samples were extracted using two protocols: a 15% v/v ethanol, 10 g/L tartaric acid extract of gently crushed berries (wine-like, WL) and a 50% v/v ethanol, pH 2 extract of grape berry homogenate. It was found that in WL extracts, grape tannin and anthocyanin concentrations were strongly related to wine tannin, anthocyanin and color density achieved during the skin contact period. No relationship was observed for grape tannin concentration analyzed in homogenate extracts and wine tannin, but a strong, positive relationship was found for anthocyanin concentration. When the data obtained from homogenate extraction was treated separately by grape variety, a stronger relationship between grape and wine tannin concentration was observed. Tannin compositional analysis in wines indicated that higher tannin concentrations were due to the extraction of tannin of higher molecular mass during fermentation, most likely from grape skins

AICc comparison of the statistical model for arrival in James Bay; Locations of groupings of automated telemetry receivers in North America; Estimates of the relationship between residual mass (relative body condition) and arrival dates to the sub-Arctic from Body condition explains migratory performance of a long-distance migrant

Table S1. AICc comparison of the statistical model for arrival in James Bay. The top 5 models are displayed, with the best model in boldface. Timing of arrival in James Bay is the response variable in all models. Departure refers to the last detection of an individual in Delaware Bay and tailwind refers to the tailwind the first 3h of the trajectory.; Fig S1. Locations of groupings of automated telemetry receivers in North America (see main text for details). The white dot indicates the capture site of Delaware Bay and the grey dot represents James Bay, located at the southern edge of the breeding grounds. The red dots indicate the fall detection sites of the Mingan Archipelago the Bay of Fundy. Maps created using R 3.3.3 using packages ggplot2, ggmap, raster and RgoogleMaps (image data providers: US Dept. of State Geographer © 2016); Fig S2. Estimates of the relationship between residual mass (relative body condition) and arrival dates to the sub-Arctic. Birds in a higher condition at the stopover site arrive earlier at the breeding grounds. Data points are estimates of linear mixed models (see main text for details), and the gray area represents 95% confidence intervals

Examples of close appositions between β-endorphin-ir fibers (red) and GnRH-GFP perikarya and processes (green) in a maximum intensity projection of the image stack (A) and in single 0.5 µm optical slices (B–D).

<p>A few close appositions were also observed between β-endorphin-ir fibers and GnRH neuroterminals in the median eminence (E), confirmed by analysis of single 0.5 µm optical slices (F). Scale bars = 15 µm (A–D), 10 µm (E), 5 µm (F).</p

Confocal microscopy revealing GFP-expressing GnRH neurons (left) and immunostaining with LR1 (right).

<p>Note that the two techniques reveal a similar number of GnRH perikarya, but the extent of the neurites is clearer using the immunohistochemical approach. Scale bars = 50 µm.</p