Scielo RSS <![CDATA[South African Journal of Enology and Viticulture]]> vol. 39 num. 2 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>The Use of SO<sub>2</sub> to Bind Acetaldehyde in Wine: Sensory Implications</b>]]> It is thought that the formation of hydroxysulphonate when sulphur dioxide is added to wine containing free acetaldehyde negates the sensory impact of the latter compound, but little research has been done on this. Descriptive analyses were employed using a trained sensory panel to assess the sensory effect of sulphur dioxide and acetaldehyde as single compounds and in combination in model wine. The addition of acetaldehyde or sulphur dioxide as singular compounds led to large increase in especially the green apple or sulphur descriptors respectively. When these two compounds were added in equimolar concentrations, the green apple description decreased drastically; however, a prominent sulphur description was still noted. It thus seems that hydroxysulphonate also has a sulphur-like aroma. The hydroxysulphonate did not influence the perception of a prominent ester, isoamyl acetate, in model wine. A low pH influences the perception of sulphur when sulphur dioxide is present on its own, but this is not the case with hydroxysulphonate. The implications of these results for wine production are discussed further. <![CDATA[<b>Identification <i>of Mgeniafuscovaria </i>(Stål)(Hemiptera: Cicadellidae), a vector of aster yellows disease on grapevines in South Africa, and differentiation from <i>Mgenia angusta </i>(Theron) by nucleotide sequences of the mitochondrial cytochrome oxidase I <i>(cox1) </i>gene</b>]]> Aster yellows phytoplasma (AY), only recently reported in South Africa and still limited in its distribution in the country, causes a serious disease of grapevine. A leafhopper, Mgenia fuscovaria (Stâl)(Hemiptera: Cicadellidae), was shown to transmit AY to grapevine (Vitis vinifera L.) locally. A second Mgenia species, identified as Mgenia angusta (Theron), has also been found in vineyards in South Africa but has not been shown to transmit AY. M. angusta is morphologically similar to M. fuscovaria, but does differ regarding the size of the male sex organ and in the number of teeth of the blades making up the ovipositor. In this study, we determined the nucleotide sequence of the mitochondrial cytochrome oxidase I gene (coxl), commonly used in insect bar-coding, of a number of specimens of males, females and nymphs of both M. fuscovaria and M. angusta. No differences were observed between the coxl sequences of the male, female and nymph specimens putatively assigned to any specific species, but some nucleotide sequence differences were observed between specimens of M. fuscovaria and M. angusta. These differences, however, were insufficient to allow the development of PCR systems specific to each species. <![CDATA[<b>Potential of Local Entomopathogenic Nematodes for Control of the Vine Mealybug, <i>Planococcus ficus</i></b>]]> Planococcus ficus, the vine mealybug, is the dominant mealybug pest of grapes in South Africa. To provide an alternative for chemical control, entomopathogenic nematodes (EPNs) were investigated as a biological control agent to be used in an integrated pest management system. Four local EPN species were screened for efficacy against female P. ficus, the most potent of which were Heterorhabditis noenieputensis, with 90% mortality, and Steinernema yirgalemense, with 63%. Since S. yirgalemense was previously shown to be highly effective against a range of pests, the effects of temperature and humidity on the infectivity of S. yirgalemense to female P. ficus were also assessed. The application of S. yirgalemense at 25°C yielded the highest mortality, of 72%, followed by 45% mortality at 30°C, and only 9% mortality when applied at 15°C. Steinernema yirgalemense performed best at 100% relative humidity (RH), resulting in 70% mortality. Decreasing RH levels resulted in decreased mortality (61% mortality at 80% RH, 40% mortality at 60% RH). As a soil-based organism, S. yirgalemense is most effective as a biocontrol agent of P. ficus under conditions of moderate temperature and high humidity. Its lethality to P. ficus, and its status as an indigenous species, indicate its promise as a potential biocontrol agent of the vine mealybug. <![CDATA[<b>Genome-wide Analysis and Expression Profiling Suggest Diverse Roles of TCP Genes During Development and Stress Responses in Grapevine <i>(Vitis vinifera </i>L)</b>]]> Teosinte branched 1/cycloidea/proliferating cell factor 1 (TCP) proteins are plant-specific transcription factors playing crucial roles in various biological processes, such as leaf development, flower symmetry, shoot branching and senescence. However, no comprehensive analysis of the TCP gene family has been reported in grapevine (Vitis vinifera L). Herein, a total of 15 TCP family members were identified in the genome of grapevine, located on eight of the 19 chromosomes. Phylogenetic and structural analyses showed that the VvTCPs were classified into two groups, designated as Class I and Class II. The Class II genes were further divided into two subclasses, the CIN subclass and the CYC/TB1 subclass. Genes belonging to the same subclass shared similar gene structures, conserved domains and motifs. Real-time PCR showed that almost all members of Class II exhibited organ-specific expression patterns, while members of Class I and the CIN Class were ubiquitously expressed in all the tissues examined, indicating multiple roles in the development of different grapevine organs. In addition, many members were strongly modulated by abiotic (cold, heat, drought) and biotic (downy mildew and powdery mildew infection) stresses, suggesting important and diverse regulatory roles in adverse conditions and plant immunity. The comprehensive in silico analysis of the grapevine TCP transcription factor family gives us some references to potential functions in grapevine development and stress responses. <![CDATA[<b>Effect of Temperature and Duration of Maceration on Colour and Sensory Properties of Red Wine: A Review</b>]]> The maceration process plays an important role in the composition of the colour and sensory properties of red wine by facilitating the extraction of phenolic and aromatic compounds found in grapes. This review summarises the key findings from a study of the literature associated with research on the effects of the temperature and duration of maceration on the phenolic content, colour and sensory properties of red wine. In the past, many researchers have reported that higher maceration temperatures increase the extraction of phenolic compounds and enhance red wine colour, but low-temperature pre-fermentative techniques have become more popular in recent years due to their positive effects on wine composition, including lower oxidation of anthocyanin pigments and aroma compounds, inhibition of undesirable enzymatic activities, and an environment that is less conductive to microbial growth. Macerations carried out at low temperature ranges (10°C to 15°C) result in red wines with the highest levels of total phenolic content, anthocyanin and colour intensity, and richer fruity, flowery and spicy aroma. The duration of maceration has also been shown to have significant effects on red wine phenolic compounds, colour properties and the relevant sensory attributes. Studies show that prolonged maceration leads to a stable red colour, as well as richer tannin content, polymeric pigments and astringency. Red wines with appropriate colour and sensory characteristics can be produced by adapting both maceration temperature and duration to the desired style. <![CDATA[<b>Interaction Effects of 3-Mercaptohexan-1-ol (3MH), Linalool and Ethyl Hexanoate on the Aromatic Profile of South African Dry Chenin blanc Wine by Descriptive Analysis (DA)</b>]]> Interaction studies are some of the most interesting sensory experiments that highlight the effect of composition on wine perception. The use of single compounds, viz. an ester (ethyl hexanoate), a terpene (linalool) and a thiol (3-mercaptohexanol, 3MH), which have previously been shown to be representative of Chenin blanc wines, resulted in typical descriptors for these compounds, such as 'apple, 'floral' and 'guava' respectively. Interaction effects were observed between the compounds, and these were reflected in both the nature and the level of attributes generated. Additionally, interaction effects between the compounds (singles and combinations) and the wine matrix indicated that the latter plays an important role in the perception of wine aromas. The use of a dearomatised neutral wine base added an extra dimension to this study, which usually is done in a simpler matrix, such as a model wine. <![CDATA[<b>Effect of Irrigation Using Diluted Winery Wastewater on the Chemical Status of a Sandy Alluvial Soil, With Particular Reference to Potassium and Sodium</b>]]> The re-use of winery wastewater for irrigation was investigated in a field trial with micro-sprinkler-irrigated Cabernet Sauvignon/99 Richter in the Breede River Valley region of South Africa. Irrigation with winery wastewater diluted with river water to 100, 250, 500, 1 000, 1 500, 2 000, 2 500 and 3 000 mg/L chemical oxygen demand (COD) was compared to irrigation with river water. No trends were found in soil pH and electrical conductivity of the saturated soil extract (ECe ) that were related to the different levels of dilution. However, ECe was considerably higher after the application of diluted winery wastewater irrigations compared to ECe at bud break. This suggests an accumulation of salts from the diluted winery wastewater. Under the prevailing conditions, soil K+ and Na+ increased with a decrease in the dilution of the winery wastewater. Increases in K+ could have a negative impact on wine colour stability should potassium be taken up by the grapevine in sufficient quantities, particularly if soil K+ accumulates to such an extent that it is luxuriously absorbed by grapevines. There were no consistent trends with regard to soil organic C, which indicates that there was too little organic material in the wastewater to have had a positive effect on soil fertility. Furthermore, organic material in the wastewater probably oxidised when the soil was aerated between irrigations. Although irrigation with diluted winery wastewater had almost no other effects, element accumulation, particularly with respect to K+ and Na+, might be more prominent in heavier soils or in regions with low winter rainfall. <![CDATA[<b>Organic Acid Metabolism and the Impact of Fermentation Practices on Wine Acidity: A Review</b>]]> The conversion of grape sugar to ethanol and carbon dioxide is the primary biochemical reaction in alcoholic wine fermentation, but microbial interactions, as well as complex secondary metabolic reactions, are equally relevant in terms of the composition of the final wine produced. The chemical composition of a wine determines the taste, flavour and aroma of the product, and is determined by many factors such as grape variety, geographical and viticultural conditions, microbial ecology of the grapes and of the fermentation processes, and the winemaking practices. Through the years, major advances have been made in understanding the biochemistry, ecology, physiology and molecular biology of the various yeast strains involved in wine production, and how these yeasts affect wine chemistry and wine sensory properties. However, many important aspects of the impact of yeast on specific wine-relevant sensory parameters remain little understood. One of these areas of limited knowledge is the contribution of individual wine yeast strains to the total organic acid profile of wine. Wine quality is indeed very directly linked to what wine tasters frequently refer to as the sugar-acid balance. The total acidity of a wine is therefore of prime sensory importance, and acidity adjustments are a frequent and legal practice in many wineries. However, the total acidity is the result of the sum of all the individual organic acids that are present in wine. Importantly, each of these acids has its own sensory attributes, with descriptors ranging from fresh to sour to metallic. It is therefore important not only to consider total acidity, but also the contribution of each individual acid to the overall acid profile of the wine. This review will summarise the current knowledge about the origin, synthesis and analysis of organic acids in wine, as well as on the management of wine acidity.