Department of Viticulture and Oenology

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Browsing Department of Viticulture and Oenology by browse.metadata.advisor "Bindon, K. A."

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    Carotenoid and chlorophyll content of Vitis vinifera cv. Merlot grapes during ripening with reference to variability in grapevine water status and vigour
    (Stellenbosch : University of Stellenbosch, 2010-03) Kamffer, Zindi; Oberholster, Anita; Bindon, K. A.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: Previous research has shown that carotenoids are precursors of C13-norisoprenoid aroma compounds in wine. C13-norisoprenoids have low threshold values in wine with the most prominent C13-norisoprenoids being β-damascanone and β-ionone which contribute honey and floral like aroma to wine. Chlorophyll and its derivates have also been detected in wine with potential to be precursors to aroma compounds. Apart from the contribution of these pigments to wine aroma and quality they are vital role players in photosynthesis and are widely found in plants and plant products. The main functions of these pigments in plants are light collection and light-protection. Research has shown that environmental conditions, climate, light exposure of bunches and soil water deficit influence the carotenoid content of grape berries. Furthermore the concentration of carotenoids and chlorophylls has also been shown to differ between cultivars. No research in this regard has been done on Merlot grape berries. With this in mind, the aim of this study was to evaluate the effect of vigour and soil water content on the evolution of carotenoids and chlorophylls through ripening of grape berries from the cv. Merlot. However, when looking at methods to analyse carotenoids and chlorophylls in berry tissue, especially lyophilised tissue, there were no readily available methods. Thus, an extraction method to identify and quantify the carotenoid and chlorophyll profile of lyophilised tissue from unripe (green) to ripe (red) Merlot grape berries was needed. In this study the RPHPLC method of Taylor et al. (2006) for carotenoids and the extraction method of Mendes-Pinto et al. (2004) were adapted to analyse both carotenoids and chlorophylls in lyophilised grape tissue. The RP-HPLC method baseline separated all the carotenoids and chlorophylls and their derivatives. Recovery of standards from mock extractions was high, indicating that the extraction procedure was acceptable. However, extraction recovery tested in the matrix of the grape tissue showed less promising results due to the high acid content of grape tissue. Violaxanthin, neoxanthin and the chlorophylls were especially sensitive to low pH conditions which facilitated their degradation. The degradation products of these compounds under acidic conditions were identified as pheophytin a, b, chlorophillide a, pyropheophytin b, cisviolaxanthin, cis-neoxanthin, neochrome, mutatoxanthin and luteoxanthin. There is a possibility that some degradation products were already present in the tissue due to lyophilisation (since the water in the berry was then removed and the acid concentrated). More work is needed to investigate the effect of lyophilisation and storage on the composition of grape tissue of different maturity. The extraction method for grape berry tissue at different ripening stages should also be optimised further to effectively neutralise tissue acidity, without compromising the extraction of carotenoids significantly, in especially green berry tissue. The question as to whether cisisomers and chlorophyll degradation products are naturally present in grape berries or are formed during sampling and processing remains unanswered in the current study. This study confirmed that in general carotenoids and chlorophylls decrease on a per berry (μg/berry) and concentration (μg/g) basis from veraison to harvest. Furthermore, this study was inconclusive in showing that vigour differences have an effect on the rate of synthesis/degradation of carotenoids, chlorophyll and some other ripening parameters, namely malic acid, total glucose and fructose, total tannin and total anthocyanin, from pre-veraison (pea size) to harvest. Additionally, no significant effect of soil water content on carotenoids, chlorophylls and ripeness parameters was found in this study, most likely due the fact that high soil water capacity was found in lower soil layers which may have prevented significant differences in grapevine water status. Experimental plots selected for vigour differences based on normalised difference vegetation index (NDVI) images, pruning mass and soil water measurements by means of a neutron probe, showed significant differences in soil water content in only the first 30 cm of the soil for the ripening seasons studied. Predawn plant water potential measurements, however, indicated that none of the experimental vines experienced severe water stress which was previously shown to effect carotenoid content of grapes. The carotenoid 5,8-epoxy--carotene was quantified for the first time in grapes and represents a significant amount of the total carotenoids present at harvest. All the carotenoids and chlorophylls except -carotene appeared to be sensitive to seasonal variation in climatic conditions. Lutein and β-carotene were found to be the most abundant carotenoids present in Merlot grape berries together with chlorophyll a for both seasons studied. The values of these carotenoids also correlated well with previous research. However, chlorophyll a was found in much larger quantities in Merlot berries compared to reported data. This is possibly because in this study the chlorophyll degradation products were included in the calculation of chlorophyll a. Multivariate analysis showed promising preliminary prediction models (with correlation values of above 0.8 for both seasons analysed) for the prediction of the concentration of ripeness parameters (glucose, fructose, malic acid, total tannins and anthocyanins) with carotenoid and chlorophyll content. This result highlights the opportunity for the development of a rapid non-destructive method to measure carotenoids and chlorophylls in berries which in turn can predict optimal ripeness. Furthermore, since carotenoids are the precursors to C13- norisoprenoid aroma compounds in wine a preview of the potential contribution of these aromas to wine might be evaluated. Further research is necessary to investigate the possibility of building and validating such models.
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    Effect of climate and soil water status on Cabernet Sauvignon (Vitis vinifera L.) grapevines in the Swartland region with special reference to sugar loading and anthocyanin biosynthesis
    (Stellenbosch : University of Stellenbosch, 2010-11-23) Mehmel, Tara Olivia; Van Heerden, Tara Olivia; Myburgh, P. A.; Deloire, A. J.; Bindon, K. A.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: Cabernet Sauvignon, the most planted red wine cultivar in South Africa, is prone to vigorous growth with low yields. The aim of the study was to describe how Cabernet Sauvignon grapevines react to climate and irrigation within the Swartland region. Such knowledge would assist growers in decisions regarding long term as well as short term cultivation practices. This study was part of a larger project carried out by the Infruitec-Nietvoorbij institute of the Agricultural Research Council at Stellenbosch to determine effects of soil type and climate on yield and wine quality of Cabernet Sauvignon. The larger project was carried out in selected grape growing regions, i.e. Stellenbosch, Swartland, Lower Olifants River and Lower Orange River. Due to the proximity to the Atlantic Ocean, the study area in the Swartland region could be divided into two climatic regions for viticulture. Grapevines near Philadelphia closer to the ocean experienced less water constraints compared to those further inland near Wellington. Variation in stem water potential could also be related to soil water matric potential. Climate tended to have a more pronounced effect on the grapevine response to water constraints further inland than closer to the ocean. Vegetative growth, berry size and yield depended on water constraints experienced by the grapevines. In the warmer climate, severe constraints reduced yield. In the warmer climate, grapes started to ripen earlier than those in the cooler climate. Sugar concentration (mg/mL) was highest where grapevines experienced moderate water constraints. These seemingly balanced grapevines had the highest sugar accumulation, probably due to optimum photosynthesis and carbohydrate utilization. Low water constraints increased vegetative growth which could have been a sink for sugar loading. In addition to sugar loading, degree Balling (°B) increases could also have been due to a concentration effect where water constraints reduced berry volume. Therefore, °B is probably not a representative indicator of grapevine functioning. Anthocyanin biosynthesis, as quantified on a per berry basis, showed that sugar and anthocyanin could be co-regulated, with anthocyanin biosynthesis reaching a plateau when the sugar content per berry reached 200 mg/mL to 220 mg/mL. At véraison, the most intense grape colour occurred where grapevines experienced moderate water constraints, i.e. single drip line at Wellington and no irrigation at Philadelphia. However, at harvest grapes from the cooler climate tended to have more intense colour and higher phenolics, indicating that lower temperatures favoured anthocyanin biosynthesis. These results supported earlier findings that grapevine water status influences berry volume and dynamics of berry ripening. Water constraints tended to increase sensorial wine colour intensity, as well as wine fullness. Moderate water constraints at both localities resulted in the best sensorial wine quality. Yet there were indications that too severe water constraints could be detrimental to wine quality. Irrigation can be used to manipulate grapevine growth in warmer climates, but might be less effective in cooler climates. In warmer climates, moderate water constraints required to achieve balanced grapevine functioning can be obtained with single drip irrigation, but this might not be the case in cooler climates.
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    Effect of shading and ethephon on the anthocyanin composition of ‘Crimson seedless’ (Vitis vinifera L.)
    (Stellenbosch : University of Stellenbosch, 2010-12) Human, Michael Adriaan; Bindon, K. A.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: ‘Crimson Seedless’ is currently one of the most important and popular table grape cultivars produced in South Africa, and as such it is of great economic value for table grape producers. Major concerns with ‘Crimson Seedless’ is that it is prone to inadequate colouring, and with increased yields the berry size decreases. An additional difficulty is that methods used to increase berry size, further impede berry colouring. A plant growth regulator (PGR) commonly used in table grape production, to enhance colour formation, is ethephon (2-chloro-ethyl-phosphonic acid, 2-CEPA). In recent years significant research has been done on the effect of sunlight on anthocyanin production in grapes, although this has primarily been on wine grape cultivars. Currently, there is limited knowledge on the effect of sunlight on table grapes, and how this might influence their anthocyanin composition and content. The effect of ethephon on colour of grapes and other fruit have been extensively researched and well documented. However, the effect of ethephon on the anthocyanin composition of ‘Crimson Seedless’ is not well known. The current study aimed to explore the effect of sunlight (by matter of exclusion) and management practices, namely defoliation and ethephon application, on the anthocyanin profile and content of ‘Crimson Seedless’. Four different treatments were applied to two ‘Crimson Seedless’ vineyards, the first site located in Paarl, and the second in De Doorns. The treatments were: 1. Naturally exposed bunches, 2. Exposed bunches treated with ethephon, 3. Bunches kept in shade boxes, 4. Shaded bunches treated with ethephon. At the De Doorns site an additional defoliation treatment was superimposed over the above treatments. An HPLC technique was modified for the separation and detailed profiling of ‘Crimson Seedless’ anthocyanins and was used to analyse the effect of the reported treatments on the anthocyanin profile of berry skins. The predominant anthocyanin in ‘Crimson Seedless’ is peonidin-3-glucoside (Pn-gluc), and this was found to be significantly increased only by ethephon application, and was not altered by sunlight or leaf removal. The responses of the other anthocyanin types varied according to the respective treatments applied. However, a general observation was that ethephon application more consistently increased the concentration of anthocyanins in berry skins than did sunlight. Leaf removal had the least significant effect on anthocyanin concentration.