Prediction of ‘Nules Clementine’ mandarin susceptibility to rind breakdown disorder using Vis/NIR spectroscopy

The use of diffuse reflectance visible and near infrared (Vis/NIR) spectroscopy was explored as a non-destructive technique to predict ‘Nules Clementine’ mandarin fruit susceptibility to rind breakdown (RBD) disorder by detecting rind physico-chemical properties of 80 intact fruit harvested from different canopy positions. Vis/NIR spectra were obtained using a LabSpec® spectrophotometer. Reference physico-chemical data of the fruit were obtained after 8 weeks of storage at 8 °C using conventional methods and included RBD, hue angle, colour index, mass loss, rind dry matter, as well as carbohydrates (sucrose, glucose, fructose, total carbohydrates), and total phenolic acid concentrations. Principal component analysis (PCA) was applied to analyse spectral data to identify clusters in the PCA score plots and outliers. Partial least squares (PLS) regression was applied to spectral data after PCA to develop prediction models for each quality attribute. The spectra were subjected to a test set validation by dividing the data into calibration (n = 48) and test validation (n = 32) sets. An extra set of 40 fruit harvested from a different part of the orchard was used for external validation. PLS-discriminant analysis (PLS-DA) models were developed to sort fruit based on canopy position and RBD susceptibility. Fruit position within the canopy had a significant influence on rind biochemical properties. Outside fruit had higher rind carbohydrates, phenolic acids and dry matter content and lower RBD index than inside fruit. The data distribution in the PCA and PLS-DA models displayed four clusters that could easily be identified. These clusters allowed distinction between fruit from different preharvest treatments. NIR calibration and validation results demonstrated that colour index, dry matter, total carbohydrates and mass loss were predicted with significant accuracy, with residual predictive deviation (RPD) for prediction of 3.83, 3.58, 3.15 and 2.61, respectively. The good correlation between spectral information and carbohydrate content demonstrated the potential of Vis/NIR as a non-destructive tool to predict fruit susceptibility to RBD

Comprehensive survey of the distribution of colour and phenolics of different red grape wine vineyard blocks from the Robertson area in South Africa

CITATION: Van der Merwe, H., Nieuwoudt, H. H., De Beer, D. & Du Toit, W. J. 2012. Comprehensive survey of the distribution of colour and phenolics of different red grape wine vineyard blocks from the Robertson area in South Africa. South African Journal of Enology and Viticulture, 33(1):58-71, doi:10.21548/33-1-1307.The original publication is available at http://www.journals.ac.za/index.php/sajevColour and phenolic content of red grapes are two of the most important constituents required to produce a quality red wine. In the Robertson grape growing area, difficulty is sometimes experienced with colour development of grapes. This is especially linked to location and most probably greatly influenced by season. Forty four vineyard blocks of the cultivars Pinotage, Merlot, Cabernet Sauvignon and Shiraz, were studied over 3 seasons primarily to focus on colour and phenolic content, but secondly on total soluble solids, titratable acidity and pH of the grapes. High performance liquid chromatography and spectrophotometric methods were used to determine various colour and phenolic parameters present at harvest. This data was used to indicate how colour and phenolic constitution of a part of the Robertson grape growing area was distributed in relation to various factors, such as cultivar and season. GPS points were used to map data for the blocks visually. Results showed variable colour and phenolic content for these grapes based on blocks and phenolic compounds investigated. Shiraz displayed a wider distribution of certain phenolic compounds over the three seasons than the other 3 cultivars. Seasonality had a great influence on these results, with outlying blocks being identified.http://www.journals.ac.za/index.php/sajev/article/view/1307Publisher's versio

Glycerol and wine

Thesis (PhD)--Stellenbosch University, 2004.ENGLISH ABSTRACT: Key research areas in modern enology are related to the production of wine of consistent quality, as well as to the improvement of existing wine quality through the enhancement of the sensory properties of wine. The formation of glycerol during alcoholic fermentation is highly relevant to both these issues. Since the early years of the zo" century, glycerol has been positively associated with the quality of wine and it is thought to impart important mouth-feel sensations such as "viscosity", "smoothness" and "body". In general, it is considered that glycerol concentrations higher than those normally found in wine, can contribute towards the improvement of wine quality. It has also been suggested that increased concentrations of glycerol can enhance the aroma of wine. On the basis of these perceptions, several strategies have been developed to favour the production of glycerol during the fermentation process and over a period of years, a large volume of data has been collected that relates to various aspects regarding glycerol production during alcoholic fermentation. To date, however, several aspects regarding the relationship between glycerol and wine quality remain unclear. The reasons for this situation can mainly be ascribed to the lack of reliable analytical data to serve as a basis for investigating the relationship between glycerol and wine quality, as well as the preponderance of empirical and anecdotal evidence. Despite numerous opinions regarding optimal glycerol concentrations in wine, glycerol is indeed seldom assayed on a routine basis and targets with respect to specific wine grape cultivars and glycerol concentrations have largely remained unspecified. To date, very little information regarding glycerol concentrations in South African wines has been published. The analytical techniques that are most frequently used for the quantification of glycerol in grape juice, fermenting must and wine are not easily automated and this aspect placed severe limitations on the generation of large volumes of analytical data on glycerol concentrations in these matrices. This project was undertaken with the aim to holistically address some of the unresolved issues relating to the relationship between glycerol and wine quality. This also implied the development and optimisation of analytical techniques suitable for the rapid and accurate determination of glycerol in fermentation media, as well as in finished wine. In the first stage of this project a quantitative database was established that contained the analytical data on the glycerol concentrations of a statistically significant number of wines of adjudged quality, as well as additional information for each wine regarding the geographic origin, vintage, routine chemical analyses and the yeast strain(s) used for the production of the wine. The relevance of glycerol in wine for the modern South African winemaker was evaluated through the establishment of a quantitative database that contained the opinions of an expert panel of 15 South African winemakers, enologists and wine chemists on topics relating to glycerol in wine. In the second stage of the project the data captured in the databases were used to investigate aspects regarding the relationship between glycerol and wine quality. From the data captured in the qualitative database, it was clear that the topic regarding glycerol in wine was important to the South African winemakers and it was also evident that there was a need for the development and optimisation of methods suitable for the routine analysis of the glycerol concentrations in grape juice, fermenting must and wine. The opinions of the panel members also highlighted the issue that the mouth-feel property of wine was considered to be an area where the quality of some wines could be further improved. The quantitative database contained the information on the glycerol concentrations of 450 commercial South African table wines of adjudged quality. The premium cultivars Chardonnay, Chenin blanc, Sauvignon blanc, Cabernet Sauvignon, Merlot, Shiraz and Pinotage were used for the purpose of investigating the relationship between glycerol concentration and wine quality. The wines represented a wide variety of wine styles, including dry white, off-dry white, dry red and late harvest wines. The average glycerol concentration was significantly associated with the wine style. In white wines the average glycerol concentration was much lower than in the red wines (6.82 gIL versus 10.49 gIL, respectively). No significant relationship between the final glycerol concentration and the geographic origin, vintage and the yeast strain used for the fermentation was found. Wine quality could not be significantly associated with glycerol concentration in the red wines. In the white wines, the relationship between glycerol concentration and wine quality was significant, but due to the very small differences in the average glycerol concentrations of the wines of different quality ratings, the statistical significance is probably of little practical value. The effect of glycerol on the volatility of a selection of esters and higher alcohols was also investigated. Solid-phase microextraction, followed by gas chromatography, was used to analyse the composition of the headspace at equilibrium between the liquid phase and the gas phase of a model wine, and a dry white wine that contained a basal concentration of 5.4 gIL glycerol. Results showed that incremental increases in the glycerol concentrations over a range of 1 -10 gIL in the model wine and in a Chenin blanc wine, were not accompanied by a proportional increase or decrease in the abundance of the aroma components in the headspace. The volatile components tested were isoamyl acetate, ethyl butyrate, ethyl valerate, ethyl lactate, ethyl hexanoate, hexyl acetate, isoamyl alcohol and isobutanol. For all the volatile components tested, the difference between the headspace composition of samples containing the lowest glycerol concentration, and those containing the highest glycerol concentration, was not significant. However, sufficient experimental evidence was obtained to indicate that increasing glycerol concentrations had an effect on the volatility of aroma components, and that the effect is of a complex and non-linear nature. In the third phase of the work Fourier transform infrared spectroscopy (FT-IR) was used to establish and optimise methods for the accurate and rapid quantification of glycerol in wine. For this purpose calibrations were developed for the quantification of glycerol in dry wine and late harvest wines. The accuracy of prediction was evaluated by means of the standard error of prediction that was 0.38 gIL for the dry wines and 0.65 gIL for the sweet wines. Large variations are introduced in the FT-IR spectra of wine by factors such as process technology, cultivar and geographic origin, and this variation can have an effect on the accuracy of the analytical data generated when employing FT-IR spectroscopy. Using glycerol prediction in wine as a model system, principal component analysis of the FT-IR spectra was done in order to establish quality control measures for the detection of poorly predicted, or outlier samples. A classification model, based on principal component analysis, was established that enabled the interpretation and classification of the outlier samples in the data set in 100% of the cases tested. This work forms the basis for expanding the quality control measures for the detection of wines of which the FT-IR spectra are highly unnatural, as well as for establishing quality control measures to ensure that accurate analytical data are generated when FT-IR is used. FT-IR spectroscopy was also used to develop a rapid screen for the evaluation of the fermentation profiles of wine yeasts. For this purpose, a selection of wine yeasts, which included commercial wine yeasts frequently used in winemaking in South Africa, as well as a selection of hybrid Saccharomyces cerevisiae yeasts, that were obtained through a selective breeding strategy aimed at increasing glycerol concentrations were used. Calibrations necessary for the accurate quantification of glycerol, volatile acidity, ethanol, reducing sugar and glucose, in Chenin blanc must and a synthetic must were developed and optimised. This work forms the basis upon which the scope of the analysis, both in terms of the number of components that can be measured, as well as the medium in which the yeasts are being evaluated, can be enlarged. This would be valuable for future applications in both the research as well as the industrial environment. The method that was developed serves to illustrate how this application can play a supportive role in yeast development programmes, through the speeding up of the initial stages of yeast strain evaluation.AFRIKAANSE OPSOMMING: Navorsing in moderne wynkunde is sterk gefokus op die produksie van wyn waarvan die kwaliteit van In volhoubare goeie peil is, sowel as die verdere verbetering van bestaande wynkwaliteit, deur In verhoging van die sensoriese eienskappe van wyn. Die vorming van gliserol tydens alkoholiese fermentasie het betrekking op beide hierdie aspekte. In Opvatting wat wyd gehuldig word en wat reeds sedert die vroeë jare van die 20e eeu geld, impliseer dat gliserol In positiewe bydrae lewer tot wynkwaliteit. Oor die algemeen word dit beskou dat gliserolvlakke hoër as wat normaalweg in wyn aangetref word, kan bydra om die kwaliteit van die wyn nog verder te vehoog. Daar is ook spekulasie dat verhoogde gliserolvlakke in wyn die intensiteit van die aroma van wyn kan verhoog. Hierdie opvattings het tot gevolg gehad dat veskeie strategieë ontwikkel is om die gliserol vlakke wat tydens die fermentasieproses gevorm word, te verhoog. Baie min inligting oor die gliserolinhoud van Suid-Afrikaanse wyn is tot onlangs gepubliseer. Ten spyte van die opvattings oor gliserol en wynkwaliteit wat reeds oor In lang tydperk gehuldig word, bly sekere aspekte van die verwantskap tussen gliserol en wynkwaliteit nog steeds onduidelik. Redes vir hierdie situasie kan hoofsaaklik toegeskryf word aan die totale afwesigheid van betroubare en substansiële eksperimentele data wat as basis kan dien vir die evaluering van die algemene opvattings aangaande die verwantskap tussen gliserol en wynkwaliteit. Die inligting wat wel beskikbaar is, is verder ook oorwegend van In empiriese aard. Huidig word gliserol selde op In roetine basis in die analitiese laboratorium bepaal, hoofsaaklik omdat die bestaande metodes tydrowend is en nie maklik geoutomatiseer kan word nie. In hierdie studie is In kwantitatiewe databasis opgestel waarin die inligting ten opsigte van die gliserolvlakke van 450 kommersiële Suid-Afrikaanse tafelwyne waarvan die kwaliteit beoordeel is, vervat is. Die kultivars Chardonnay, Chenin blanc, Sauvignon blanc, Cabernet Sauvignon, Merlot, Shiraz en Pinotage is gebruik vir hierdie doel en die seleksie van wyne was verteenwoordigend van In wye verskeidenheid wynstyle, insluitende droë wit-, halfdroë wit-, droë rooi- en laatoeswyne. Die gemiddelde gliserolvlakke in die witwyne was heelwat laer as die gemidelde gliserolvlakke in die droë rooiwyne (6.82 gIL teenoor 10.49 gIL, onderskeidelik). Geen beduidende verwantskap kon aangetoon word tussen die gliserolkonsentrasie in die wyn en die geografiese oorsprong, oesjaar, en die gisras wat gebruik is in die produksie van die wyn nie. Die kwaliteit van rooiwyn kon nie beduidend met die gliserolkonsentrasie geassosieer word nie. In die geval van wit wyn was die verwantskap statisties beduidend, maar die verskille was klein en moontlik nie van veel praktiese waarde nie. Die aktualiteit van gliserol vir die moderne Suid-Afrikaanse wynmaker is geëvalueer op grond van die opinies van In paneel van 15 Suid-Afrikaanse kundiges, rakende aspekte wat verband hou met die algemene opvattings oor gliserol en wyn. Die paneel het bestaan uit wynmakers, wynkundiges en chemici. Die opinie van die panel is deur middel van "n vraelys bekom en is vervat in "n kwalitatiewe databasis. Die resultate van hierdie menigspeiling het getoon dat gliserol wel vir die Suid- Afrikaanse wynmakers belangrik is en dit het ook die behoefte uitgewys vir die ontwikkeling en optimisering van metodes wat geskik is vir die roetine analyses van gliserol in wyn. Die invloed van gliserol op die vlugtigheid van "n seleksie van hoëralkohole en esters is ondersoek in "n model wyn sowel as "n wit wyn, waarvan die basiese gliserolkonsentrasie 5.4 gIL was. Soliede-fase mikroekstraksie van die gasfase van wyn is opgevolg met "n gaschromatografiese analise. Resultate het getoon dat "n stapsgewyse toename in die gliserol konsentrasie, oor "n konsentrasie reeks van 0 - 10 gIL in die model wyn, en 0 - 15 gIL in die wit wyn, nie gepaard gegaan het met "n reglynige toename of afname in die konsentrasie van die aromakomponente nie. Vir al die komponente wat ondersoek is, was die samestelling van die gasfase in monsters wat die laagste gliserol konsentrasie gehad het, teenoor dié wat die hoogste gliserol konsentrasie gehad het, nie beduidend nie. Nietemin het die resultate getoon dat gliserol wel "n effek het op die vlugtigheid van die aroma komponente wat in hierdie ondersoek gebruik is, maar dat die aard van die effek kompleks en nie-liniê is. Fourier-transformasie-infrarooispektroskopie (FT-IR) is gebruik om die metodes vir die analise van gliserol in wyn sodanig te optimiser, dat vinnige en akkurate bepalings op "n roetine basis in wyn gedoen kan word. Kalibrasies is ontwikkel vir die kwantifisering van gliserol in droëwyn en laatoeswyn. Die standaard voorspellingsfout van die kalibrasies wat ontwikkel is, was 0.38 gIL in droëwyn en 0.65 gIL in die geval van laatoeswyn. Inherente variasie in die FT-IR-spektra word deur eksterne faktore soos die proses tegnologie wat gebruik is om die wyn te berei, die kultivar en geografiese oorsprong van die wyn veroorsaak en hierdie variasie kan "n effek hê op die voorspelingsakkuraatheid van FT-IR spektroskopie. Om die effek van hierdie variasie op die akkuraarheid van die analitiese data te evalueer, is die voorspelling van gliserol as modelsisteem gebruik. Hoofkomponentanalise van die FT-IR spektra is gedoen om dié wyne met onnatuurlike FT-IR-spektra te identifiseer, ten einde beheer oor die akkuraatheid van die analitiese data uit te oefen. "n Verdere model wat ook gebaseer is op hoofkomponentanalise van die FT-IR-wynspektra is ontwikkel vir die interpretasie en klassifikasie van wynmonsters met onnatuurlike FT-IRspektra. Met die model wat ontwikkel is kon onnatuurlike wynmonsters met "n akkuraatheid van 100% gëidentifiseer word. Hierdie werk vorm die basis waarop kwaliteitsbeheer verder uitgebrei kan word sodat wyne met onnatuurlike spektra gëidentifiseer kan word, sowel as om te verseker dat akkurate data gegenereer word as FT-IR as analitiese metode gebruik word vir die kwantifisering van gliserol in wyn. FT-IR spektroskopie is ook gebruik om "n vinnige skandeerproses te ontwikkel waarmee die fermentasieprofiele van wyngiste geëvalueer kan word. Die seleksie giste wat vir hierdie doel gebruik is, sluit kommersiële Suid-Afrikaanse wyngiste in, sowel as hibriede Saccharomyces cerevisia-giste wat normaalweg hoër vlakke van gliserol tydens die fermentasieproses produseer. Kalibrasies is ontwikkel vir die akkurate kwantifisering van gliserol, vlugtige suur, alkohol, reduserende suiker en glukose, in Chenin blanc-mos sowel as in 'n sintetiese medium. Hierdie werk vorm die basis waarop verdere uitbreidings gedoen kan word, sodat meer metaboliete gemeet kan word en 'n groter verskeidenheid van fermentasiemedia gebruik kan word. Hierdie ontwikkeling is waardevol vir toekomstige toepassings in die navorsings- sowel as die industriële omgewing. Die metode wat ontwikkel is illustreer ook hoe hierdie toepassing 'n ondersteunende rol kan speel in wyngisontwikkelingsprogramme deur die aanvanklike evalueringsproses van die giste te versnel

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Optimisation of the quantification of total soluble solids, ph and titratable acidity in South African grape must using Fourier transform mid-infrared spectroscopy

CITATION: Swanepoel, M., Du Toit, M. & Nieuwoudt, H. H. 2007. Optimisation of the quantification of total soluble solids, ph and titratable acidity in South African grape must using Fourier transform mid-infrared spectroscopy. South African Journal of Enology & Viticulture, 28(2):140-149, doi:10.21548/28-2-1467.The original publication is available at http://www.journals.ac.za/index.php/sajevCalibration models for Fourier transform mid-infrared (FT-MIR) spectroscopy were developed for the simultaneous quantification of total soluble solids (TSS, measured as °Brix), pH and titratable acidity (TA, expressed as g/L tartaric acid) in South African (SA) grape must. An exploratory data analysis of the FT-MIR spectra of 1170 grape must samples (647 for °Brix, 252 for pH and 271 for TA) was done by principal component analysis, and partial least squares regression was used for the computation of the regression models. The prediction errors for TSS (0.34°Brix), pH (0.04 units) and TA (0.51 g/L) provided analytical data of satisfactory accuracy. The evaluation of readyto-use global calibrations to quantify these three parameters in SA samples presented standard error of prediction (SEP) values of 0.46°Brix, 0.10 pH units and 3.13 g/L for TA. After slope and intercept adjustments of the original global calibration algorithms, the SEP values were reduced to 0.38 °Brix, 0.05 pH units and 0.49 g/L for TA. These results show the necessity for optimisation of the global FT-MIR WineScan calibrations to provide a better fit to samples of South African origin. The results demonstrate that FT-MIR spectroscopy is a useful technique for the rapid quantification of major grape must parameters and for quality control purposes in an industrial cellar.http://www.journals.ac.za/index.php/sajev/article/view/1467Publisher's versio

Trained sensory panellists' response to product alcohol content in the projective mapping task: Observations on alcohol content, product complexity and prior knowledge

acceptedVersio

Sorting in combination with quality scoring: A tool for industry professionals to identify drivers of wine quality rapidly

Quality plays an important role in the criteria directing wine product development. The evaluation of sensory characteristics associated with wine quality, as perceived by industry professionals, is therefore important. We investigated the suitability of the free-sorting sensory evaluation method, in combination with wine quality scoring using a 20-point scoring system, to determine the drivers of quality. Eight commercial South African Sauvignon blanc wines were assessed by a panel of 24 wine industry professionals. Free sorting with a verbalisation step to describe the groups, followed by quality scoring using score sheets routinely used in the wine industry, was performed. A multivariate sensory map was constructed using DISTATIS to explain the similarities and differences amongst the set of wines. Correspondence analysis (CA) was applied to the group descriptors, and CA deviates were calculated. Pearson’s correlation coefficients between CA deviates and the quality scores were calculated to identify the drivers of quality. Significant differences in quality were observed between the wines. The sensory attributes “passion fruit”, “green pepper”, “peas”, “asparagus” and “green” were frequently cited by the panel for the wines that received the highest average quality scores, and these attributes were identified as drivers of quality. In this study, a procedure is presented that combines sorting and quality scoring to investigate the relationship between sensory attributes and quality scores to identify the drivers of wine quality. Industry professionals and research environments can use this procedure to determine drivers of wine quality in a single evaluation session.publishedVersio

Fermentation-derived aroma compounds in varietal young wines from South Africa

The original publication is available at http://www.sasev.org/.The volatile composition of 925 single cultivar young Sauvignon blanc, Chardonnay, Pinotage, Merlot, Shiraz and Cabernet Sauvignon wines of vintages 2005 to 2007, was determined using gas chromatography-flame ionisation detection. Compositional data were compared to published data on young wines from South Africa and other countries. South African young wines analysed in this study had a largely similar volatile composition to that reported in the literature. Significant between-vintage and between-cultivar differences were observed in the volatile composition of the wines investigated in this study. The concentration ranges of four compounds in red wines, hexanol, propanol, diethyl succinate and ethyl lactate, and four compounds in white wines, 2-phenylethanol, hexanoic acid, isoamyl acetate and propanol, were not influenced by vintage effects. This finding was interpreted as the first indication that typical concentration ranges for some aroma compounds can be established for South African young cultivar wines. A trend was observed in the white wines that the alcohols and their respective acetate esters, as well as fatty acids and their ethyl esters, were responsible for the vintage-related effects. Differences in volatile composition between Chardonnay and Sauvignon blanc wines could also largely be explained on the same basis. Classification models were established to discriminate between individual red wine cultivars and between the two white wine cultivars and correct classification rates of respectively, 79 % and 85 % were achieved.Publishers' versio

Glycerol in South African table wines : an assessment of its relationship to wine quality

CITATION: Nieuwoudt, H. H., et al. 2002. Glycerol in South African table wines : an assessment of its relationship to wine quality. South African Journal of Enology & Viticulture, 23(1):22-30, doi:10.21548/23-1-2151.The original publication is available at http://www.journals.ac.za/index.php/sajevGlycerol is an important by-product of glycolysis and is quantitatively one of the major components of wine. While the physicochemical and sensory characteristics of pure glycerol are well established, the impact of varying levels of glycerol on general wine quality remains a topic of debate. Previous reports have relied on limited numbers of either commercial or experimental wines to assess the role of glycerol, leading to contradictory conclusions. Here we report on a large-scale assessment of the relationship between glycerol concentration and wine quality, based on the analysis of a significant number of commercial South African table wines of adjudged quality. The mean glycerol concentrations of 237 dry red (10.49 g/L), 158 dry white (6.82 g/L), 22 off-dry white (6.55 g/L), 16 special late harvest (8.26 g/L) and 14 noble late harvest wines (15.55 g/L) were found to be associated with considerable variation within each respective style. The final glycerol concentrations were significantly associated with the wine style (P0.05). The mean glycerol concentrations for South African dry red wines were significantly higher than those of dry white and off-dry white wines. Wine quality could not be significantly associated with glycerol concentrations in the dry red wines (P>0.05). For the dry white, off-dry white and late harvest wines this association was significant (P<0.05), although the exact nature of the association was somewhat different for the respective styles. Despite this positive statistical association, the observed differences between the mean glycerol concentrations of dry white and off-dry white wines of different quality ratings were too small to be of major practical value. The relationship between glycerol concentration and wine quality is reassessed on the basis of results obtained in this study as well as on recent reports in the literature.http://www.journals.ac.za/index.php/sajev/article/view/2151Publisher's versio