13 research outputs found
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
Commercial Saccharomyces cerevisiae Yeast Strains Significantly Impact Shiraz Tannin and Polysaccharide Composition with Implications for Wine Colour and Astringency
To gain knowledge on the role of Saccharomyces cerevisiae yeast strains (and their hybrids) on wine sensory properties, 10 commercially available yeast strains were selected on the basis of their widespread usage and/or novel properties and used to produce Shiraz wines. Significant differences were evident post-alcoholic fermentation and after 24 months of ageing with regards to the number of wine compositional variables, in particular the concentration of tannin and polysaccharide. Strain L2323 is known for its pectinolytic activity and yielded the highest concentration of both yeast- and grape-derived polysaccharides. Wines made with the mannoprotein-producing strain Uvaferm HPS (high levels of polysaccharides) did not have elevated concentrations of yeast-derived polysaccharides, despite this observation being made for corresponding model fermentations, suggesting that mannoprotein production or retention might be limited by the wine matrix. Wine tannin concentration showed a high level of variability between strains, with L2323 having the highest, and AWRI1503 the lowest concentration. Sensory analysis of the wines after 24 months ageing revealed significant differences between the yeast strains, but only the attributes opacity (visual colour) and astringency could be predicted by partial least squares regression using the wine compositional data. Notably, the astringency attribute was associated with higher concentrations of both tannin and polysaccharide, contrary to reports in the literature which suggested that polysaccharide exerts a moderating effect on astringency. The results confirm previous reports demonstrating that the choice of yeast strain represents an opportunity to shape wine style outcomes
Properties of Wine Polymeric Pigments Formed from Anthocyanin and Tannins Differing in Size Distribution and Subunit Composition
To
explore the effect of tannin composition on pigment formation,
model ferments of purified 3-<i>O</i>-monoglucoside anthocyanins
(ACN)
were conducted either alone or in the presence of two different tannins.
Tannins were isolated from grape seeds (Sd) or skins (Sk) following
exhaustive extraction in 70% v/v acetone. The Sd and Sk tannin fractions
had a mean degree of polymerization of 5.2 and 25.6, respectively.
The Sd fraction was highly galloylated, at 22%, but galloylation was
<2% in the Sk fraction. The Sk fraction was distinguished by a
high proportion of prodelphinidin, at 58%. After a 6 month aging period,
polymeric pigments were quantified and their color properties determined
following isolation by solid-phase extraction. Wine color and polymeric
pigment were highest in the treatment containing ACN+Sd and similar
in the ACN+Sk and ACN treatments. The same trend between treatments
was observed for total and polymeric nonbleachable pigments. Only
minor changes in tannin subunit composition were found following ACN
incorporation, but the size distribution of polymeric pigments determined
by gel permeation chromatography decreased, in particular for the
ACN+Sk treatment. Color incorporation in the higher molecular mass
range was lower for ACN+Sk wines than for ACN+Sd wines. Compositional
differences between the two tannin fractions may therefore limit the
incorporation of ACNs in the colored form. The results suggest that
in the ACN+Sk and ACN treatments, the formation of lower molecular
mass oligomeric pigments was favored. In polymeric pigments derived
from ACNs, the presence of ethyl- and vinyl-linked ACNs to the level
of trimers was identified using mass spectrometry
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
Rapid measurement of methyl cellulose precipitable Ttannins using ultraviolet spectroscopy with chemometrics: application to red wine and inter-laboratory calibration transfer
Information relating to tannin concentration in grapes and wine is not currently available simply and rapidly enough to inform decision-making by grape growers, winemakers, and wine researchers. Spectroscopy and chemometrics have been implemented for the analysis of critical grape and wine parameters and offer a possible solution for rapid tannin analysis. We report here the development and validation of an ultraviolet (UV) spectral calibration for the prediction of tannin concentration in red wines. Such spectral calibrations reduce the time and resource requirements involved in measuring tannins. A diverse calibration set (n = 204) was prepared with samples of Australian wines of five varieties (Cabernet Sauvignon, Shiraz, Merlot, Pinot Noir, and Durif), from regions spanning the wine grape growing areas of Australia, with varying climate and soils, and with vintages ranging from 1991 to 2007. The relationship between tannin measured by the methyl cellulose precipitation (MCP) reference method at 280 nm and tannin predicted with a multiple linear regression (MLR) calibration, using ultraviolet (UV) absorbance at 250, 270, 280, 290, and 315 nm, was strong (r(2)val = 0.92; SECV = 0.20 g/L). An independent validation set (n = 85) was predicted using the MLR algorithm developed with the calibration set and gave confidence in the ability to predict new samples, independent of the samples used to prepare the calibration (r(2)val = 0.94; SEP = 0.18 g/L). The MLR algorithm could also predict tannin in fermenting wines (r(2)val = 0.76; SEP = 0.18 g/L), but worked best from the second day of ferment on. This study also explored instrument-to-instrument transfer of a spectral calibration for MCP tannin. After slope and bias adjustments of the calibration, efficient calibration transfer to other laboratories was clearly demonstrated, with all instruments in the study effectively giving identical results on a transfer set.Robert G. Dambergs, Meagan D. Mercurio, Stella Kassara, Daniel Cozzolino, and Paul A. Smit