Department of Viticulture and Oenology

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Basic in-mouth attribute evaluation : a comparison of two panels
(MDPI, 2018-12-21) Mihnea, Mihaela; Aleixandre-Tudo, Jose Luis; Kidd, Martin; Du Toit, Wessel
Astringency is often difficult to evaluate accurately in wine because of its complexity. This accuracy can improve through training sessions, but it can be time-consuming and expensive. A way to reduce these costs can be the use of wine experts, who are known to be reliable evaluators. Therefore, the aim of this work was to compare the sensory results and the panel performance obtained using trained panelists versus wine experts (winemakers). Judges evaluated twelve red wines for in-mouth basic perception (sweet, sour, bitter, astringent, and burning sensation) following the same tasting protocol and with the samples being presented in two different tasting modalities. Panels’ performance and relationship between the chemical composition and the sensory perception were investigated. Both panels showed similar consistency and repeatability, and they were able to accurately measure the astringency of the wines. However, the significant correlations between sensory scores and chemical composition varied with the panel and the tasting modality. From our results, we could see that winemakers tended to discriminate better between the samples when the differences were very small.
Bibliometric and social network analysis in scientific research on precision agriculture
(Indian Academy of Sciences, 2018-11-10) Aleixandre-Tudo, Jose Luis; Castello-Cogollos, Lourdes; Aleixandre, Jose Luis; Aleixandre-Benavent, Rafael
Precision agriculture (PA) is used to improve agricultural processes. A better understanding of PA as well as the evolution of the research status through the available literature are reported and discussed in this study. The Web of Science (WoS) was used to obtain the research records under study. Indicators of scientific productivity, collaboration between countries and research impact were evaluated through a social network analysis. The keywords included in the publications and subject areas under which the research was published were also evaluated through subject analysis. A total of 2027 articles were analysed from 1994 to 2014. The most productive journals were ‘Computers and Electronics in Agriculture’ (n = 191) and ‘Precision Agriculture’ (n = 110). The most frequent keywords were ‘management’ (n = 243), ‘yield’ (n = 231), ‘soil’ (n = 198) and ‘variability’ (n = 190). The collaboration network showed the United States occupying a central position, in combination with some leading countries such as Brazil, Germany, People’s Republic of China, Canada, Australia and Spain. A steady increase in PA research was identified during the last decade, which was even more sharp between 2010 and 2014. The increased importance of PA research has recently led to the birth of specific journals such as Precision Agriculture. The increasing number of journals that publish articles related to the topics included in the WoS must also be considered. The network analysis identified a number of developed countries in the hotspot of international collaboration.
A chemometric approach to the evaluation of the ageing ability of red wines
(Elsevier, 2020) Aleixandre-Tudo, Jose Luis; Toit, Wesseldu
One of the most important quality attributes of red wines is its ability to withstand and ageing process. The multidimensionality of the ageing ability concept, which includes a combination of colour, taste, mouthfeel, and aroma was reported in previous studies. Phenolic compounds are largely or partially involved in most of these wine attributes and have been proposed as potential candidates to evaluate the ageing ability of red wines. The phenolic and colour properties of a large number of wines were measured during a barrel and bottle ageing process of 24 months. To our understanding, a wine that needs the longest time to reach optimal phenolic quality is considered a wine with higher ability to age (concentration assumption). Moreover, a wine that is able to maintain its optimal phenolic quality for longer will also be a wine with high ageing ability (stability assumption). Based on the formulated assumptions a scoring system was used to identify those wines with theoretically high ability to age. As expected, these wines contained initial high levels of tannins, total phenols and anthocyanins, including high polymeric pigment presence and enhanced colour properties. Interestingly, high ageing ability wines showed a smaller change in the colour properties over time which might be indicating slower pigment formation rates. In addition, a chemometric attempt was undertaken to explore an ageing index based on initial phenolic content. The evolution of the index over time using a multi-block approach showed stability for the index values, in line with the short term stability of tannin and total phenol levels. Finally, promising results were obtained as two thirds of the wines were correctly classified when a validation task between the ageing index and the score values was attempted.
Effect of skin contact before and during alcoholic fermentation on the chemical and sensory profile of South African Chenin Blanc white wines
(South African Society for Enology and Viticulture, 2015) Aleixandre-Tudo, Jose Luis; Weightman, C.; Panzeri, V.; Nieuwoudt, Helene; Du Toit, W. J.
The volatile and phenolic composition of Chenin blanc wines made with different skin contact treatments was studied. One batch of grapes was used to make a dry white wine according to two different treatments, namely pre-fermentative skin contact and complete fermentation on the skins. A white wine fermented without any skin contact was used as control. Fermentation on the skins and skin contact before fermentation led to significantly lower levels of terpenes, esters, acids and thiols, and the highest significant levels of alcohols and phenolic compounds. However, this effect was less pronounced in wines with skin contact before fermentation. Sensory analysis of all the experimental wines was also performed. The results showed a significant shift from the sensory attributes of fresh and tropical fruits of the control Chenin blanc wines towards riper fruit notes in the skin contact treatments. This observation was correlated with the length of the skin contact period. Possible reasons to explain the results observed in this study are discussed.
Infrared spectroscopy and chemometric applications for the qualitative and quantitative investigation of grapevine organs
(Frontiers Media S.A, 2021-09-03) Van Wyngaard, Elizma; Blancquaert, Erna; Nieuwoudt, Hélène; Aleixandre-Tudo, Jose Luis
The fourth agricultural revolution is leading us into a time of using data science as a tool to implement precision viticulture. Infrared spectroscopy provides the means for rapid and large-scale data collection to achieve this goal. The non-invasive applications of infrared spectroscopy in grapevines are still in its infancy, but recent studies have reported its feasibility. This review examines near infrared and mid infrared spectroscopy for the qualitative and quantitative investigation of intact grapevine organs. Qualitative applications, with the focus on using spectral data for categorization purposes, is discussed. The quantitative applications discussed in this review focuses on the methods associated with carbohydrates, nitrogen, and amino acids, using both invasive and non-invasive means of sample measurement. Few studies have investigated the use of infrared spectroscopy for the direct measurement of intact, fresh, and unfrozen grapevine organs such as berries or leaves, and these studies are examined in depth. The chemometric procedures associated with qualitative and quantitative infrared techniques are discussed, followed by the critical evaluation of the future prospects that could be expected in the field.
Partial least squares calibrations and batch statistical process control to monitor phenolic extraction in red wine fermentations under different maceration conditions
(2020-04-11) Fourie, Elzanne; Aleixandre-Tudo, Jose Luis; Mihnea, Mihaela; Du Toit, Wessel
The extraction of phenolic compounds during maceration is of utmost importance in red winemaking. However, the monitoring of phenolic extraction is often hampered by analytical and statistical constraints. The aim of this study was to monitor phenolic extraction kinetics with the use of PLS phenolic calibrations and batch statistical process control. Eight batches of Cabernet Sauvignon and Shiraz grapes during alcoholic fermentation under different maceration conditions (pressing at 1/3rd, 2/3rd and end of fermentation) and punch down regimes (low vs. high frequency) were evaluated in the study. Cabernet Sauvignon appeared to be a more suitable cultivar for longer maceration conditions with increased tannin extraction observed. Similar trends were observed for punch down for both cultivars. The use of PLS calibrations and batch level modelling provided an enhanced interpretation and understanding of phenolic extraction during red wine fermentations.
The role of UV-visible spectroscopy for phenolic compounds quantification in winemaking
(2019) Aleixandre-Tudo, Jose Luis; Du Toit, Wessel
Phenolic compounds are bioactive substances present in a large number of food products including wine. The importance of these compounds in wine is due to their large effect on the organoleptic attributes of wine. Phenolic compounds play a crucial role in the colour as well as mouthfeel properties of wines. UV-visible spectroscopy appears as a suitable technique for the evaluation of phenolic compounds’ properties and content. The ability of the phenolic ring to absorb UV light and the fact that some of the phenolic substances are coloured compounds, i.e. show absorption features in the visible region, make UV-visible spectroscopy a suitable technique to investigate and quantify grape and wine phenolic compounds. A number of analytical techniques are currently used for phenolic quantification. These include both simpler approaches (spectrophotometric determinations) as well as more complex methodologies such liquid chromatography analysis. Moreover, a number of spectroscopy applications have also been recently reported and are becoming popular within the wine industry. This chapter reviews information on the UV-visible spectral properties of phenolic compounds, changes occurring during wine ageing and also discusses the current UV-visible based analytical techniques used for the quantification of phenolic compounds in grapes and wine.

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