- ItemInfrared 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 LuisThe 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.
- ItemInvestigation of olfactory interactions of low levels of five off-flavour causing compounds in a red wine matrix(Elsevier, 2019) McKay, Marianne; Bauer, Florian F.; Panzeri, Valeria; Buica, AstridThe qualitative sensory perception of individual and of complex mixtures of five compounds, guaiacol (‘burnt note’), o-cresol (‘phenolic/tar’), 4-ethylphenol (4-EP, ‘leather/barnyard’), 2-iso-butyl-3-methoxypyrazine (IBMP, ‘green pepper/herbaceous’), and 2,4,6-trichloroanisole (TCA, ‘cork taint/ mouldy’) were tested in a partially de-aromatised red wine matrix using descriptive analysis by a trained panel of eleven judges. Compounds were characterised at peri- and sub-threshold concentrations using a partial D-optimal statistical design and response surface methodology. Results indicated that complex mixtures in red wine elicit an olfactory response that could not be predicted from the attributes or descriptors of single compounds. Positive sweet/fruity attributes were more intense in solutions containing fewer off-flavour compounds. Novel findings of this study include that IBMP at sub- and peri-threshold levels shows perceptual interaction with volatile phenols at the same levels, and samples containing combinations of these compounds manifested herbaceous and burnt characteristics. Olfactory interactions of this many off-flavour compounds have not been investigated previously in one study. The findings have direct implications for wines made from cultivars that are known to contain these compounds, and add to the understanding of the behaviour and impact of very low levels (peri- and sub-threshold) of volatile phenols, IBMP, and TCA derived from various sources during winemaking.
- ItemPartial 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, WesselThe 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.
- ItemA chemometric approach to the evaluation of the ageing ability of red wines(Elsevier, 2020) Aleixandre-Tudo, Jose Luis; Toit, WesselduOne 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.
- ItemThe role of UV-visible spectroscopy for phenolic compounds quantification in winemaking(2019) Aleixandre-Tudo, Jose Luis; du Toit, WesselPhenolic 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.