Browsing by Author "Buica, Astrid"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Investigation 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, Astrid
    The 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.
  • Thumbnail Image
    Item
    Measuring thiols in single cultivar South African red wines using 4,4-dithiodipyridine (DTDP) derivatization and ultraperformance convergence chromatography-tandem mass spectrometry
    (MDPI, 2018) Mafata, Mpho; Stander, Maria A.; Thomachot, Baptiste; Buica, Astrid
    Wine varietal thiols are important contributors to wine aroma. The chemical nature of thiols makes them difficult to measure due to low concentrations, high sensitivity to oxidation, and low ionization. Methods for the measurement of thiols usually consist of multiple steps of sample preparation followed by instrumental measurement. Studies have collected large datasets of thiols in white wine but not in red wine, due to the lack of availability of suitable methods. In this study, for the first time, convergence chromatography was used to measure thiols in red wine at ultratrace levels with improved sensitivity compared to previous methods. Performance parameters (selectivity, linearity, limits of detection, precision, accuracy) were tested to demonstrate the suitability of the method for the proposed application. Red wine thiols were measured in South African Pinotage, Shiraz, and Cabernet Sauvignon wines (n = 16 each). Cultivar differentiation using the thiol profile was demonstrated.
  • Thumbnail Image
    Item
    Measuring thiols in single cultivar South African red wines using 4,4-dithiodipyridine (DTDP) derivatization and ultraperformance convergence chromatography-tandem mass spectrometry
    (MDPI, 2018-08-30) Mafata, Mpho; Stander, Maria A.; Thomachot, Baptiste; Buica, Astrid
    Wine varietal thiols are important contributors to wine aroma. The chemical nature of thiols makes them difficult to measure due to low concentrations, high sensitivity to oxidation, and low ionization. Methods for the measurement of thiols usually consist of multiple steps of sample preparation followed by instrumental measurement. Studies have collected large datasets of thiols in white wine but not in red wine, due to the lack of availability of suitable methods. In this study, for the first time, convergence chromatography was used to measure thiols in red wine at ultratrace levels with improved sensitivity compared to previous methods. Performance parameters (selectivity, linearity, limits of detection, precision, accuracy) were tested to demonstrate the suitability of the method for the proposed application. Red wine thiols were measured in South African Pinotage, Shiraz, and Cabernet Sauvignon wines (n = 16 each). Cultivar differentiation using the thiol profile was demonstrated.
  • Thumbnail Image
    Item
    Testing the sensitivity of potential panelists for wine taint compounds using a simplified sensory strategy
    (MDPI, 2018-10-24) McKay, Marianne; Bauer, Florian; Panzeri, Valeria; Buica, Astrid
    The odor detection threshold (ODT) of a compound is the lowest concentration at which individuals can reliably perceive a difference between a sample and its corresponding control, with 50% performance above chance. Wine is a complex matrix, and ODTs used in studies on wine can be based on inappropriate matrices and informal sensory methodologies. Formal studies confirming ODTs in wine are relatively scarce in the literature, and are complex and expensive to carry out. In this study, the sensitivity of panelists to previously published ODTs for five compounds: Guaiacol, o-cresol and 4-ethyl phenol, 3-isobutyl-2-methoxypyrazine (IBMP), and 2,4,6-trichloroanisole (TCA) associated with off-flavor/taint issues in wine, was investigated. The study was carried out in partially de-aromatized young Shirazwine (unwooded) using a simplified version of the formal sensory approach. A triangle test in triplicate was carried out with 34 panelists, at the ODT for each compound, in one day. The study explored whether previous training affected panelists’ sensitivity for threshold differences. Results showed that samples spiked with volatile phenols were significantly different (p = 0.01) to controls. The spiked TCA and IBMP samples were not significantly different from the control in either case. Judges were better able to detect compounds if they had prior experience or training in wine evaluation. Despite some limitations, this pragmatic approach may be useful when carrying out sensory studieswith fairly limited resources andwithin tight timelines, as it provides helpful information on panel members and detection thresholds for a specific matrix.
  • Thumbnail Image
    Item
    Unravelling the complexities of wine : a big data approach to yeast assimilable nitrogen using InfraRed spectroscopy and chemometrics
    (International Viticulture and Enology Society, 2019-04-26) Petrovic, Gabriella; Aleixandre-Tudo, Jose-Luis; Buica, Astrid
    Aim: Assimilable Nitrogen (YAN) has been identified as one of the main drivers of wine quality, influencing the production of various aromas and ensuring a successful fermentation to dryness. Due to the number of factors affecting YAN concentration and composition, paired with the complexities of yeast metabolism, more data is required to enable a comprehensive understanding of this important component of the grape juice matrix. The use of high throughput and information-rich techniques such as InfraRed spectroscopy can lead to a fast generation of a large amount of data. In addition, there is a possibility to maximise the information output of the generated data when combined with various descriptive and exploratory statistical techniques. Conclusion: Given the recent developments in the fields of analytical equipment and chemometrics, the review explores the possibility of a Big Data approach for the research of one of the most important and versatile grape juice parameters, namely YAN.