Extraction and bioconversion of aroma impact compounds from Sauvignon Blanc grapes to wine matrices during white wine production

Greyling, Isabel (2019-12)

Thesis (MScAgric)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: The phenotypic response of Sauvignon Blanc grapes grown in high light (HL) conditions has been shown to acclimate to stress conditions via photoprotective responses that includes the upregulation of specific grape metabolites. These metabolites are typically concentrated in the berry skins and include aroma compounds/precursors, photosynthetic pigments and polyphenolic compounds which contribute to the distinctive aroma of the resulting wines. The fate of these aroma impact metabolites from the grape tissues during juice processing and fermentation up until the final wine has been studied and revealed a highly dynamic environment involving metabolite bioconversions and/or interaction. The aim of this study was to profile selected aroma-related metabolites in Sauvignon Blanc grape berries that were exposed to high light (HL) and low light (LL) microclimates and to follow the fate of the metabolites throughout the key processing stages of winemaking. Two winemaking procedures that could potentially affect the extraction of aroma-related metabolites from grape skins and juice sediment (particulate grape debris) were evaluated. The impact of the various factors (vineyard microclimate, skin contact and fermentation with grape sediment) on the sensory profile of the wine was also determined. Berries grown in the HL environment contained higher concentrations of grape derived aroma-linked metabolites (including IBMP, limonene, linalool, 6-MHO and hexyl formate) confirming previously published results. These berries were therefore characterised as having higher aromatic potential (HAP) compared to the berries from the LL microclimate with lower aromatic potential (LAP). During juice processing there was a dramatic decrease in the aromatic potential in both HAP and LAP juices and the chemical analysis of the sediment could account for many of the “lost” compounds. Thus, we established that the sediment represents a reservoir of untapped aromatic potential. The distinction between HAP and LAP berries persisted throughout juice processing up to the final wines when prepared by standard winemaking (Std) procedures. The main difference between HL-Std and LL-Std wines where in the concentration of grape derived aroma compounds with the formercontaining significantly higher concentrations of IBMP, hotrienol, linalool and β-damascenone. Confirming previous studies, the LL-Std wines had a vegetative sensorial character and the HL-Std wines were fruity. Modulations to the standard winemaking procedure to investigate enhanced extraction of aroma metabolites included a skin contact treatment before pressing and fermentation in contact of the sediment formed during juice clarification. Skin contact (Sc) mitigated the loss in aroma potential seen during juice processing and increased hexyl formate, hotrienol and IBMP concentration in both LAP and HAP juice. The corresponding skin contact wines contained higher concentrations of linalool, IBMP and 3-MH. Interestingly LL-Sc wines had a similar chemical and especially sensory profile to HL-Std and HL-Sc wines. This demonstrated that the aromatic potential of LAP berries (with additional extraction) is adequate to alter the aromatic potential of wine. Wines fermented in contact with the sediment were enriched by the metabolites that were detected in the sediment and this enrichment effect was stronger than what was achieved with skin contact. These wines had significantly higher concentrations of hexyl formate, IBMP and 3MH, but had lower ester levels and malodours were perceived during sensorial analysis. This study provided insights into the transfer and fate of the aromatic potential of Sauvignon Blanc from the grapes, throughout juice processing onto the final wine. It highlights the impacts of viticultural manipulations and winemaking steps that aims to improve aroma compound extraction on the aromatic potential and sensory profile of the wine.

AFRIKAANSE OPSOMMING: Studies het gewys dat Sauvignon Blanc druiwe wat in ‘n hoë-lig (HL) mikroklimaat gekweek is ‘n sekere fenotiepiese respons toon om by streskondisies aan te pas. Die respons sluit fotobeskermende meganismes in wat tot die ooruitdrukking van spesifieke druifmetaboliete lei. Hierdie metaboliete versamel hoofsaaklik in die druiwedoppe en sluit aroma komponente en hul voorgangers, fotosintetiese pigmente en polifenoliese verbindings wat almal bydra tot die kenmerkende aroma van die wyne wat daarvan geproduseer word. Die roete en uiteindelike lot van hierdie aroma impak-metaboliete is bestudeer in die druiwe, tydens sap verwerking en fermentasiestappe, tot en met die finale wyn. Hierdie benadering het die hoogs dinamiese aard van die wynmaakproses, gekenmerk deur metaboliet bio-omskakelings en/of interaksies, uitgewys. Die doel van hierdie studie was om ‘n profiel te verkry van gekose aroma verwante metaboliete in Sauvignon Blanc druiwe, wat afkomstig was van twee verskillende mikroklimate, naamlik ‘n hoë lig (HL) en lae lig (LL) mikroklimaat. Die aroma verwante metaboliete is bepaal in die druiwe en daarna “gevolg” tydens die hoof stappe van die wynmaak proses. Twee wynmaakprosedures is geëvalueer op grond van hulle vermoë om die ekstraksie van aroma verwante metaboliete vanuit druiwedoppe, asook sapsediment (druifmateriaal wat uitsak na ensiem geïnduseerde sapverheldering) te beïnvloed. Die invloed van die verskillende faktore (wingerd-mikroklimaat, dopkontak en gisting in die teenwoordigheid van sapsediment) op van die wyn se sensoriese profiel is ook bepaal. Druifkorrels afkomstig vanaf die HL-mikroklimaat, het hoër konsentrasies van aroma-verwante metaboliete (insluitend IBMP, limoneen, linalool, 6-MHO en heksielformaat) bevat, in lyn met voorheen gepubliseerde resultate. Die HL druifkorrels het dus 'n hoër aromatiese potensiaal (HAP) gehad, in kontras met dié van die LL-mikroklimaat wat 'n laer aromatiese potensiaal (LAP) vertoon het. Tydens die verwerking van sap was daar 'n merkwaardige afname in die aromatiese potensiaal van beide HAP- en LAP-sappe. Chemiese ontleding van die sediment het die teenwoordigheid van baie van hierdie “verlore” metaboliete aangedui wat uitwys dat die sediment 'n moontlike “reservoir” vir onbenutte aromatiese potensiaal verteenwoordig. Tydens standaard wynmaak prosedures (Std) het die verskille tussen HAP- en LAP-druiwe, van sap tot die finale wyne, behoue gebly. Die grootste verskil (in terme van aroma-verwante metabolitee) tussen die samestelling van HL-Std en LL-Std wyne, was dat eersgenoemde aansienlik hoër konsentrasies IBMP, hotrienol, linalool en β-damascenoon bevat het. Sensoriese analiese het bevestig wat in vorige studies gevind is: die LL-Std wyn het ‘n vegetatiewe karakter gehad, terwyl die HL-Std wyne beskryf is met ‘n “vrugtige” sensoriese karakter, ondanks die relatief hoë IBMP-vlakke in die wyne. Aanpassings in die standaard wynmaakprosedure is gemaak met die doel om die ekstraksie van aroma-verwante metaboliete te versterk, en het dopkontak (voor pars) en ‘n sediment kontak behandeling (tydens fermentasie) ingesluit. Dopkontak (Sc) het die verlies aan aroma potensiaal wat tydens sapverwerking gesien is, tot ‘n sekere mate teengewerk en die heksielformaat-, hotrienol- en IBMP-konsentrasie in beide LAP- en HAP-sap verhoog. Die ooreenstemmende dopkontakwyne het voorts hoër konsentrasies van linalool, IBMP en 3-MH bevat. Interessant genoeg het LL-Sc-wyne 'n soortgelyke chemiese en veral sensoriese profiel as HL-Std- en HL-Sc wyne gehad. Dit het getoon dat die aromatiese potensiaal van LAP-druiwe (met ekstra ekstraksie) voldoende is om die aromatiese potensiaal van die wyn te verander. Wyn wat in kontak was met die sediment tydens fermentasie, was verryk met die metaboliete wat in dié matriks gevind word. Hierdie verrykingseffek was groter as dit wat met dopkontak verkry is. Die sedimentkontakwyne het merkwaardige hoër konsentrasies van heksielformaat, IBMP en 3MH gehad, maar laer konsentrasies van esters, en afgeure is ook bespeur tydens sensoriese analise. Hierdie studie het gelei tot waardevolle insigte in die oordrag en “lot” van die aromatiese potensiaal van Sauvignon Blanc-druiwe, vanaf die druif, deur die wynmaak prosedure tot in die finale wyn. Dit werp lig op die gevolge van wingerdmanipulasies, asook aanpassings in wynmaakstappe wat daarop gemik is om die ekstraksie van aroma verwante metaboliete te verbeter, veral op die uituidelike impakte op die aromatiese potensiaal en sensoriese profiele van die finale wyne.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107309
This item appears in the following collections: