Changes in Grape Maturity Induced by Spraying Ethanol

Three different ethanol solutions were sprayed onto Cabernet Sauvignon (Vitis vinifera L.) clusters during the ripening period: 2.5, 5 and 10% by volume in water. Controls were sprayed with water alone. Three different times of spraying were also tested: 8, 10 and 13 weeks post-flowering. One of the observed changes was a lower titratable acidity in grape samples at harvest, when the clusters were sprayed with ethanol at 10 weeks, in comparison with controls. The wines made with grapes treated with ethanol after mid-veraison, had higher ODs at 520 nm than did the controls. This may due to a combined effect of red pigment levels and acidity. In addition, following malolactic fermentation, the acidity levels of wines made with ethanoltreated grapes were slightly higher than those made with the control grapes. Spraying ethanol at 13 weeks post-flowering increased the berry weight by 10% at harvest without decreasing the °Brix value. The corresponding wines had similar degrees of alcohol. This observation was made for the first time in 2001

Ethanol triggers grape gene expression leading to anthocyanin accumulation during berry ripening

Recent studies have shown that low doses of ethanol stimulate the maturation of some fruits. The present work showed that spraying Cabernet Sauvignon grapes, with 5% ethanol at veraison enhances the anthocyanin accumulation. Veraison is the time when the berries turn from green to purple. HPLC analysis showed a marked increase in the total concentrations of the derivatives of delphinidin, cyanidin, petunidin, peonidin and malvidin from the fourth day after the ethanol treatment until harvest. This was not linked to a difference in berry weight in comparison to controls. Two distinct expression patterns were found for anthocyanin biosynthesis genes in the treated and untreated berries. For one group, consisting of chalcone synthase, flavanone-3-hydroxylase, dihydroxyflavonol-4-reductase and leucoanthocyanidin dioxygenase, the expression was inhibited or unchanged by the ethanol treatment, whereas for UDP glucose-flavonoid 3-O-glucosyltransferase (UFGT) there was a marked increase in expression from 1 to 20 days after ethanol treatment. These results suggest that the UFGT gene is a key factor in the observed anthocyanin accumulation following ethanol treatment

Evidence for host-associated clones of grape phylloxera Daktulosphaira vitifoliae (Hemiptera : Phylloxeridae) in Australia

Grape phylloxera, Daktulosphaira vitifoliae Fitch, is an important pest of grapevines (Vitis vinifera L.) (Vitaceae). Using microsatellite DNA markers it was demonstrated strong associations can exist between D. vitifoliae asexual lineages and vine host type within a vineyard. Also, in excised root bioassays, D. vitifoliae collected from three regions where different genotypic classes predominated showed host-specific differences in life table parameters of reproductive rate and intrinsic rate of increase. Lastly, comparisons of mitochondrial DNA (cytochrome oxidase I) sequences revealed that D. vitifoliae in Australia have paraphyletic origins and fall into two clades partially related to vine host usage. These findings indicate introduction of separate lineages of D. vitifoliae which have close host associations and as such, have important implications for management of this pest in Australia.A.M. Corrie, R. van Heeswijck and A.A. Hoffman

Metabolic engineering of Rhizopus oryzae for the production of platform chemicals

Rhizopus oryzae is a filamentous fungus belonging to the Zygomycetes. It is among others known for its ability to produce the sustainable platform chemicals l-(+)-lactic acid, fumaric acid, and ethanol. During glycolysis, all fermentable carbon sources are metabolized to pyruvate and subsequently distributed over the pathways leading to the formation of these products. These platform chemicals are produced in high yields on a wide range of carbon sources. The yields are in excess of 85 % of the theoretical yield for l-(+)-lactic acid and ethanol and over 65 % for fumaric acid. The study and optimization of the metabolic pathways involved in the production of these compounds requires well-developed metabolic engineering tools and knowledge of the genetic makeup of this organism. This review focuses on the current metabolic engineering techniques available for R. oryzae and their application on the metabolic pathways of the main fermentation products

In vitro systems for studying the interaction of root-knot nematode with grapevine

The original publication can be found at www.springerlink.comA simple system for in vitro dual culture of grapevine (Vitis spp.) plantlets and root-knot nematode (Meloidogyne javanica (Treub) Chitwood) is described. Based on the presence or absence of mature females, or the total number of nematodes in the roots after 36-day co-culture, the system reliably discriminated resistant (cv. Ramsey) and susceptible (cv. Chardonnay) grapevines. The system was sensitive enough to differentiate between infestation levels of cvs Borner and Chardonnay, both susceptible in the in vitro conditions. A modification of the system to use plantlets from rooted petioles has reduced labour and space requirements and would suit mass screening of grapevine genotypes in traditional or genetic engineering-based breeding programmes. In both systems, nematodes in roots of cv. Ramsey tended to be associated with brown tissue and, compared with those in roots of cv. Chardonnay, were more likely to be con. ned to tips rather than be distributed along the root after co-culture for 11 or 36 days.Tricia K. Franks, Sandra Savocchia and Robyn Van Heeswijc

Models for predicting wine fermentation kinetics

Fermentation of grape juice by yeast is a critical stage in industrial wine production. However, the kinetics of the process are poorly understood due to the extreme conditions present during such fermentations. Problematic fermentations occur regularly and result in significant cost as a result of wasted tank capacity and low value of the final degraded product. Control of the fermentation process is important to avoid 'stuck fermentations' (a stuck fermentation is a fermentation that has stopped before all the available sugar in the wine has been converted to alcohol and CO2) and clearly, the fermentation unit operation strongly influences the aesthetic endcharacteristics of the wine. A variety of models have been proposed to predict the dynamic behaviour (kinetics) of the process. Two traditional and simple biochemical models (Monod kinetics and the Gompertz model) are predominantly employed and these were investigated in this work. The primary aim of this study was to determine the ability of both models to predict fermentation behaviour when fitted to data from early stages of fermentation. Initially, the Monod and Gompertz models were fitted to sugar consumption data for laboratory scale wine fermentations using least squares regression. The model produced a reasonable qualitative fit for the kinetic (growth and production) data with a root-mean-squared error (RMS) of 21 g/L or less in each case. Both models were then fitted to sugar consumption data from twenty two industrial fermentations over a varying number of time steps following the initial measurement in each data set. The number of time steps required to produce an RMS error less than 20 g/L was 8 days in 19 cases using the Monod model. However, the Gompertz model (successful in 18 cases) generally required 2 – 4 fewer time steps (days). No correlation was found between the number of time steps required or the regressed parameters and the volume of fermentation. The values of the regressed Monod parameters maximum growth rate (μm), the Monod constant (KS) and the yield coefficient (YX/S) lay between 0.1 – 1.0 day-1, 200 – 1000 g/L and 0.01 – 0.10 g cell X/g substrate (assumed to be sugar content) S in most cases, with deviations loosely correlated to the use of Semillon grapes. Both models exhibited promise for use in industry alongside traditional winemaking techniques, depending upon the specific goals and requirements of each individual winery. Rigorous error analysis was not possible due to a lack of supplied experimental uncertainty data and this will be investigated in future work.Brian O'Neill, Torbjorn van Heeswijck and Richard Muhlackhttp://www.chemeca2011.com