Department of Biochemistry

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Browsing Department of Biochemistry by browse.metadata.advisor "Buica, Astrid"

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    To target or not to target: strategies for the aroma analysis of alcoholic beverages
    (Stellenbosch : Stellenbosch University, 2023-12) Williams, Cody; Buica, Astrid; Stander, Marietjie A.; Medvedovici, Andrei V.; Stellenbosch University. Faculty of Science. Dept. of Biochemistry.
    ENGLISH ABSTRACT: Classically, targeted analysis has dominated analytical chemistry research, whereby analytical methods are required for separation, identification and quantitation of specific analytes of interest. The complex wine, gin and beer matrices contain several hundreds of compounds, each with varying concentration levels and unique chemistries. Furthermore, comprehensive analysis of these alcoholic beverages are challenging, as suitable instrumentation and data handling strategies are required to effectively profile these matrices. The use of non-targeted methodologies emerge as an alternative tool used for profiling the aroma space of alcoholic beverages. Non-targeted analysis is an information rich technique which focuses on profiling a sample in its entirety. More data can equal more information, however more noise is also generated; thus, suitable strategies are highly desired to overcome this caveat. The question is now, are these strategies complementary or is the generated information redundant? The aim of this dissertation was to compare targeted and non-targeted strategies for the aroma analysis of wine, beer and gin. This dissertation is comprised of seven chapters showing the evolution of both targeted and non- targeted strategies starting with wine and culminating in the application of these strategies in craft gin and beer, together with the evaluation of the results using appropriate (and sometimes complex) statistical tools. The first part of the study is a comprehensive literature review, with specific focus on terpenoid analysis. Terpenoids are an integral component to the sensory profile in wine, beer and gin. These compounds are present in various concentrations and require advanced analytical tools to profile and quantify. The origin of terpenoids as derived from the raw materials or production practices, common concentration ranges, and sample preparation methods are reported. The use of non-targeted methods is also summarised in this review for wine, beer and gin, with particular focus on the use of hyphenated instrumentation, software processing tools, and multivariate statistical analysis. The first objective (chapter 3) focused on targeted strategies in wine. Terpenoids were selected due to their importance to the aroma profile and inherent challenges associated with the analysis of these compounds. The complexity associated with the analyses stimulated interest and prompted further investigation in the quantitation of terpenoids in wine. Two sample preparation strategies, namely offline-SPE and online-HS-SPME were explored for the quantitation of 20 terpenoids in red and white wine. This study documented which sample preparation was best for the quantitation of terpenoids in wine and reported on various method performance parameters. The second objective (chapter 4) expanded on the quantitation of terpenoids in wine, whereby the method was expanded from 20 to 53 terpenoids in a single method. This was accomplished through method development, optimisation and method performance characterisation. In addition, terpenoid stability was evaluated over a period of forty days. As this extended method includes compounds not found in wine, it was applied to craft gin (n=21) and craft beer (n=34) samples, and it documents for the first time the most terpenoids quantified in a single method using authentic standards. It also constitutes the first report on terpenoids quantified in South African craft gin and beer. In the non-targeted space, the third objective (chapter 5) highlights the use of various sample prepration strategies (LLE, SPE and HS-SPME) applied to wine of different cultivar (Chenin Blanc, Sauvignon Blanc and Chardonnay) and winemaking style (wooded and unwooded). The data was acquired using a non-targeted profiling method and processed using cloud metabolomics software, XCMS online, followed by multivariate analysis. Importantly, the pipeline methodology for this approach was established to characterise both qualitative and quantitative information on the wine samples. This strategy enabled the identification of the most sensitive and best profiling sample preparation method. In addition, this application conceptualises a pipeline methodology approach, whereby sample preparation, instrument analysis, cloud data processing and multivariate analysis is applied in order to obtain meaningful relationships in complex data sets. As an extension of the targeted and non-targeted strategies reported, the fourth and final objective (chapter 6) showcases an application of this pipeline methodology to craft beer (n=91) and gin (n=67). Craft beer and gin samples were analysed using the targeted terpenoid and non-targeted profiling strategies. Subsequent data processing and curation allowed for application to multivariate statistical analysis. The configurational similarity was compared to reveal differences between the targeted and non-targeted strategies. Further insight was made into identifying characteristic biomarkers for distinguishing between lager-style and ale-style craft beers.