Linking sensory attributes to selected aroma compounds in South African Cabernet Sauvignon wines

Lapalus, Emmanuelle (2016-03)

Thesis (MSc)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: Cabernet Sauvignon is a widely planted red grape cultivar which produces worldwide, some of the finest and most expensive red wines. The typical aroma of Cabernet Sauvignon wines is often described as either fruity and berry-like or vegetative, herbaceous and green; the latter descriptors are often considered undesirable. High levels of 2-isobutyl-3-methoxypyrazine (ibMP), a powerful grape-derived compound, have been associated with greener notes in Cabernet Sauvignon wines. Over the past two decades, extensive research has been conducted worldwide to identify the active odorants that impact the aromatic profiles of Cabernet Sauvignon wines. These compounds are mostly higher alcohols, esters, C13- norisoprenoids, methoxypyrazines, sulphur compounds and certain terpenes. More recent studies have endeavoured to establish a relationship between the sensory analysis and chemical composition of these wines as it could help to explain the impact of certain odorants on the perception of either fruity or herbaceous notes. Despite the interest shown by the South African wine industry to improve the quality of Cabernet Sauvignon wines, no such study has been conducted in South Africa yet. The first part of this study gives an overview of the major active aroma compounds which have been identified in Cabernet Sauvignon wines with a particular focus on volatile compounds that could exhibit either fruity berry notes or herbaceous/vegetative notes. Some of the findings of studies conducted in Australia and the United States are also discussed. The second part of this study investigates the relationship between the volatile composition and sensory properties in 13 mono-varietal Cabernet Sauvignon wines produced in South Africa. The wines were selected to represent a broad range of fruity and herbaceous sensory attributes and were assessed by descriptive analysis. A limited number of volatile compounds (33 in total) that could contribute to either fruity or herbaceous characters, as indicated in the literature, were analysed using either headspace solid phase micro extraction (SPME) and gas chromatography–ion trap mass spectrometer detection (HS-SPME-GC-ion trap-MS analysis) or solid phase extraction (SPE) and gas chromatography coupled with a triple quadrupole detector (SPE-GC-MS/MS analysis). The statistical treatment by multiple factor analysis (MFA) of both compositional data and sensory data showed that certain volatile compounds such as ß- damascenone, ß-ionone, dimethylsulphide (DMS) and ibMP predicted well some of the aroma attributes used to describe the selected wines. It was found that the analysis of ß-damascenone, ß-ionone, 3-mercaptohexyl acetate, dimethyl sulphide and ibMP could be of interest for winemakers wanting to explain certain typical aroma descriptors characterising South African Cabernet Sauvignon wines.

AFRIKAANSE OPSOMMING: Cabernet Sauvignon is ‘n algemeen aangeplante rooidruif-kultivar wat wêreldwyd sommige van die beste and duurste rooiwyne produseer. Die tipiese aroma van Cabernet Sauvignon-wyne word gereeld as óf vrugtig en bessieagtig óf vegetatief, kruidagtig en groen beskryf; laasgenoemde beskrywende terme word in baie gevalle as ongewens beskou. Hoë vlakke van 2-isobutiel-3-metoksipirasien (ibMP), ‘n kragtige druifafgeleide verbinding, is reeds met die groener note in a Cabernet Sauvignon-wyne geassosieer. Oor die afgelope twee dekades is breedvoerige navorsing wêreldwyd onderneem om die aktiewe geurstowwe wat die aromatiese profiele van Cabernet Sauvignon-wyne beïnvloed, te identifiseer. Hierdie verbindings is meesal hoër alkohole, esters, C13-norisoprenoïede, metoksipirasiene, swaelverbindings en sekere terpene. Meer onlangse studies het gepoog om ‘n verhouding te bepaal tussen die sensoriese analise en chemiese samestelling van hierdie wyne, aangesien dit sou kon bydra tot die verklaring van die impak van sekere geurstowwe op die waarneming van óf vrugtige óf kruidagtige note. Ten spyte van die belangstelling wat deur die Suid-Afrikaanse wynbedryf daarin getoon is om die kwaliteit van Cabernet Sauvignon-wyne te verbeter, is geen sulke studies tot op hede in Suid-Afrika onderneem nie. Die eerste deel van hierdie studie verskaf ‘n oorsig van die vernaamste aromaverbindings wat reeds in Cabernet Sauvignon-wyne geïdentifiseer is, met ‘n spesifieke fokus op vlugtige verbindings wat óf vrugtige bessienote of kruidagtige/vegetatiewe note kon vertoon. Sommige van die bevindings van studies wat in Australië en die VSA onderneem is, word ook bespreek. Die tweede deel van hierdie studie ondersoek die verhouding tussen die vlugtige samestelling en sensoriese eienskappe in 13 enkelvariëteit Cabernet Sauvignon-wyne wat in Suid-Afrika geproduseer is. Die wyne is gekies om ‘n breë verskeidenheid van vrugtige en kruidagtige sensoriese eienskappe te verteenwoordig en is deur middel van beskrywende analise geassesseer. ‘n Beperkte aantal vlugtige verbindings (33 in totaal) wat óf tot die vrugtige óf die kruidagtige karakters kon bydrae, soos in die literatuur aangedui, is deur middel van óf lugspasie-analise (headspace solid phase micro extraction (SPME)) en gaschromatografie–ion trap massaspektrometrie waarneming (gas chromatogoraphy–ion trap mass spectrometer detection (HS-SPME-GC-ion trap-MS)) óf soliede fase ekstraksie (solid phase extraction (SPE)) en gaschromatografie tesame met ‘n a triple quadrupole detector (SPE-GC-MS/MS analise). Die statistiese behandeling deur veelvuldige faktor-analise (multiple factor analysis (MFA)) van beide die kompositoriese data en die sensoriese data het getoon dat sekere vlugtige verbindings, soos ß-damaskenoon, ß-ionoon, dimetielsulfied (DMS) en ibMP, sommige van die aroma-eienskappe wat gebruik word om die geselekteerde wyne te beskryf, goed voorspel het. Daar is gevind dat die analise van  ß-damaskenoon,  ß-ionoon, 3-merkaptoheksiel asetaat, dimetielsulfied en ibMP van belang kan wees vir wynmakers wat sekere van die tipiese aromabeskrywers wil verklaar wat Suid-Afrikaanse Cabernet Sauvignon-wyne karakteriseer.

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