Linking the phenolic potential of grape berries with polyphenol distribution during wine making : a Sauvignon Blanc case study.

Williams, Davin Lance (2019-04)

Thesis (MScAgric)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: The focus of this study was the phenolic potentials of grape and wine matrices of Sauvignon Blanc produced in either a high or low light microclimate. Phenolic compounds are important in grapes due to their protective function against environmental stress and fungal infection. In ripe grapes, polyphenols are unequally distributed as the skin is rich in flavonols, the seeds in flavan-3-ols, whereas the pulp contains low quantities of hydroxycinnamic acids. The polyphenol content of grapes can be altered through viticultural treatments such as manipulating the light microclimate of the bunches during development. Maintenance of a high light microclimate typically enhances polyphenol accumulation, thus increasing the phenolic potential of the grapes. The polyphenols that are present within the grapes are extracted to the derived juice and wine during winemaking where these compounds could influence colour as well as the sensory perception of wine. The extraction of phenolic compounds into the juice can be enhanced by modulating the winemaking steps, such as incorporating extended pre-fermentative skin contact. This modulation is mostly excluded in white wine-making due to potential negative implications of a high polyphenol content on white wine properties. In general, much less information on polyphenols is available for white grapes and wines. The aim of this study was to profile and quantify the phenolic potentials of Sauvignon Blanc grapes and to “follow” the compounds throughout the wine-making process, in all the grape and wine matrices, including the waste products. Pomace and juice sediments generated during winemaking and discarded as wastes can be considered as “traps” for phenolic compounds that accumulate in them. These waste matrices, when analysed alongside the juice and wine matrices could provide valuable information on the fate of polyphenols throughout the wine-making process. The approach in this study was to contrast Sauvignon Blanc grapes and wines that were exposed to two microclimates that differed in terms of the light exposure in the bunch zone. The study benefitted from a fully characterised model vineyard site where grapes from a high light (HL) and low light (LL) microclimate could be sourced. The first step was to profile and quantify the polyphenolic content and composition of the whole grapes, as well as their skins, pulps and seeds. The results confirmed previous findings that the berries from the HL environment accumulated significantly more polyphenols and that it was mostly the skins and to a lesser degree the pulp that responded to increased exposure by producing certain polyphenols. The flavonols found in the skins were strongly upregulated by the high light microclimate. The results confirmed that the two microclimates yielded berries with distinctly different phenolic potentials (a high phenolic potential, HP from the HL microclimate and a low phenolic potential (LP from the LL microclimate). In addition to the flavonols, certain hydroxycinnamic acids and flavan-3-ols could be quantified in this study. The next objective was to compare a standard white-wine making procedure (as the control) with modulated wine-making steps chosen to allow enhanced extraction of the polyphenols from the grape matrices of the HP and LP grapes. Enhanced extraction was modulated by implementing either pre-fermentative skin contact, fermentation in contact with the juice sediment, or a combination of these two treatments in the making of the wines. In addition to profiling and measuring the polyphenolic compounds in the juices, wines and waste matrices, the impact of the treatments on the sensorial quality of the wine was also evaluated from a mouthfeel perspective. Polyphenol transference occurred only partially from the grapes to the juice as no flavonols nor flavan-3-ols originating from the seeds were detected in the latter. During juice processing, total polyphenol levels also decreased considerably from the free run to the enzyme clarified juice as both hydroxycinnamic acids and flavan-3-ol concentrations decreased. This decrease was primarily linked to a decrease in catechin and caftaric acid which were the most abundant polyphenols in the juice matrix. Analysis of the corresponding sediment revealed that a considerable quantity of already extracted polyphenols settled out of suspension after enzyme clarification of the juice. Analysis of the pomace revealed that a fraction of polyphenols were also not extracted from the berry and remained in the pomace regardless of treatment, but the pomace was also considered as a phenolic trap due to flavonoid increases after pressing. The phenolic composition of the pomace also correlated with the fresh grape skin but contained lower quantities of polyphenols. The increase in total polyphenol content of the juices, which included hydroxycinnamic acids and flavan-3-ols, through pre-fermentative skin contact was in agreement with literature. The phenolic compounds that were increased in the juice were also higher in the corresponding sediments but did not clearly reflect in the pomace. The analysis method used to determine the cell wall composition of the pomace did not indicate significant alteration during the juice processing steps but the juice data revealed that sufficient deconstruction must have occurred to allow extraction of more phenolic compounds. In the standard and skin contact clarified juice made from high phenolic potential grapes, only the concentrations of catechin and caffeic were elevated in comparison to the low phenolic potential juice. High phenolic potential grapes in combination with skin contact yielded juices with higher total polyphenol content but mainly due to elevated levels of catechin. The phenolic profiles of the standard and skin contact wines correlated with the phenolic profiles of their preceding juices. Sediment contact during fermentation increased the total polyphenol content of all wines, specifically the flavan-3-ols, and more so in the high phenolic potential wine. The phenolic potential along with treatments induced perceptible differences on the sensorial characteristics of the wines. Standard high phenolic potential wines were less bitter than its low phenolic potential counterparts. Skin contact increased wine sweetness whereas sediment contact increased bitterness. This study provided new insight into the transference of polyphenols during white wine making as well as the potential implications of phenolic potential of grapes and additional wine making treatments on transference and the organoleptic properties of the wine.

AFRIKAANSE OPSOMMING: Die fokus van hierdie studie was die fenoliese potensiaal van Sauvignon Blanc druif- en wyn matrikse wat in hoë of lae lig mikroklimate geproduseer was. In druiwe funksioneer fenole as beskermingsagente wat weerstand teen omgewingsstres en swaminfeksies bied. Fenole is oneweredig versprei in die ryp druiwekorrel: die doppe bevat hoë vlakke van flavonole, die sade bevat flavan-3-ole en die pulp het lae vlakke van hidroksiekaneelsure. Die fenoliese vlakke van die druiwe kan deur wingerdboukundige behandelinge verander word, byvoorbeeld deur die lig mikroklimaat waarin die druifkorrel ontwikkel te manipuleer. Die handhaweing van ‘n hoë lig mikroklimaat verhoog fenoliese opeenhoping, sodoende ook die fenoliese potensiaal van die druiwe. Die fenole in die druiwe word na die sap en wyn ge-ekstraheer tydens die wynmaak proses, en beïnvloed die kleur asook sensoriese persepsie van die wyn. Die ekstraksie kan verhoog word deur die aanpas van wynmaak stappe, soos die insluiting van verlengde dopkontak voor fermentasie. Hierdie modulerende stap word meestal uit die witwynmaak prosedure uitgesluit as gevolg van die moontlike negatiewe gevolge wat tipies verbind word met hoë vlakke van fenole in witwyn. Oor die algemeen is daar minder inligting beskikbaar rakende fenole in wit druiwe in vergelyking met dit wat bekend is vir rooi druiwe. Die doel van hierdie studie was om die fenoliese profiel en -potensiaal van Sauvignon Blanc druiwe te bepaal en om hierdie verbindings te volg deur die wynmaak proses, in al die druif- en wyn matrikse, asook in die afvalmateriaal. Druifprosesserings afval soos doppe en sap sediment wat gedurende wynmaak gegenereer en gewoonlik weggegooi word, kan as fenoliese “lokvalle” beskou word vir die verbindings wat daarin akkumuleer. Wanneer hierdie afvalmatrikse saam met die sap en wyn geanaliseer word, kan waardevolle inligting rakende die lot van fenoliese verbindings gedurende die wynmaak proses ingewin word. Die aanslag van hierdie studie was om Sauvignon Blanc druiwe and wyn vanaf twee mikroklimate, wat verskil in terme van ligblootselling, te vergelyk. Hierdie studie het gebaat by ‘n ten volle gekaraktariseerde “model” wingerd waar bewys is dat hoë lig (HL) en lae lig (LL) mikroklimaat-druiwe gelewer kan word. Die eerse stap was om die profiel van die fenoliese verbindings in die heelkorrels, asook in die doppe, pulp en pitte te kwantifiseer. Die uitslag dat druiwe vanaf die HL mikroklimaat meer fenole geakkumuleer het en dat dit meerendeels die doppe en tot ‘n mindere mate die pulp was wat geaffekteer was, het resulte van vorige studies bevestig. Die flavonool opbou in die doppe was sterk opgereguleer deur die HL mikroklimaat. Die uitslag het bevetsig dat die twee mikroklimate druifkorrrels geproduseer het met duidelik onderkeibare fenoliese potensiale (‘n hoë fenoliese potensiaal, vanaf die HL mikroklimaat; en ‘n lae fenoliese potensiaal, vanaf die LL mikroklimaat). Bykomend tot die flavonole, kon sekere hidroksiekaneelsure en flavan-3-ole akkuraat gemeet word in hierdie studie. Die volgende doelwit was om ‘n standaard witwynmaak prosedure (kontrole) te vergelyk met gemoduleerde wynmaak prosedures, wat spesifiek geskies was om verhoogde fenoliese ekstraksie vanuit die HP en LP druiwe toe te laat. Dopkontak voor fermentasie, sediment kontak gedurende fermentasie, óf ‘n kombinasie van die twee is uitgetoets om ekstraksie te verhoog. Tesame met die kwantifisering en bepaling van die fenoliese profiel van die sap-, wyn- en afvalmatrikse, is die impak van hierdie behandelinge op die sensoriese kwaliteit van die wyn in terme van die mondgevoel, ook bepaal. Polifenoliese oordrag vanaf die druiwe na die sap het slegs gedeeltelik plaasgevind, want geen flavonole of flavan-3-ole (oorspronklik afkomstig vanaf die pitte) was teenwoordig in die sap nie. Gedurende die verwerking van die sap was daar ‘n afname in totale polifenoliese vlakke vanaf die afloopsap na die ensiem-verhelderde sap, aangesien beide hidroksiekaneelsure en flavan-3-ole verminder het. Hierdie verlaging was hoofsaaklik veroorsaak deur ‘n verlaging in katikiene (“catechins”) en kofarsuur (“caftaric acid”), wat die vollopste fenoliese verbindings in die sap was. Die ooreenstemmende sediment matriks het onthul dat ‘n groot hoeveelheid ge-ekstraheerde fenole, in die sediment uitsak na ensiem behandeling van die sap. Die ontleding van die druiwedopafval het aangedui dat ‘n fraksie fenole nie vanuit die druif ge-ekstraheer was nie en in die druiwedopafval agter gebly het ongeag of dopkontak toegepas is. Die druiwedopafval kan dus as ‘n fenoliese lokval beskou word aangesien die flavonoiëd konsentrasie toegeneem het na die pers stap. Die polifenoliese samestelling van die druiwedopafval het ooreenkomste met die vars druiwedoppe getoon, maar het laer vlakke van polifenole gehad. Die toename in totale polifenoliese inhoud van die sap (wat hidroksiekaneelsure en flavan-3-ole insluit) as gevolg van dopkontak het vorige bevindings in literatuur bevestig. Die fenoliese verbindings wat in die sap toegeneem het, was ook hoër in die ooreenstemmende sediment, maar het nie ooreenkomstig in die druiwedopafval gereflekteer nie. Die analitiese metode wat gebruik was om die selwandsamestelling van die druiwedopafval te bepaal, het nie noemenswaardige veranderinge gedurende sap verwerking aangedui nie, maar die sap data het bewys dat selwand dekonstruksie wel tot ‘n mate moes plaasgevind het om uitloging van meer fenole toe te laat. In die standaard- en dopkontak verhelderde sap, gemaak van LP druiwe, het slegs die konsentrasie van katikiene en kafeïensuur verhoog in vergelyking met die LP sap. HP druiwe in kombinasie met dopkontak het sappe gelewer met hoër totale fenoliese vlakke, hoofsaaklik as gevolg van hoër katikienvlakke. Die fenoliese profiel van die standaard en dopkontakwyne het ooreengestem met die fenoliese profiel van hul ooreenkomstige sappe. Sediment kontak gedurende fermentasie het ’n toename in totale fenoliese vlakke van alle wyne, veral flavan-3-ole veroorsaak, en wel tot ‘n groter mate in die HP wyne. Die fenoliese potensiaal, tesame met die behandelinge het ook opmerkbare verskille in die sensoriese eienskappe van die wyne veroorsaak. Standaard HP wyne was minder bitter in vergelyking met die standaard LP wyne. Dop kontak het oor die algemeen wyne soeter gemaak, in teenstelling met die verhoging in bitterheid wat versoorsaak was deur sediment kontak. Hierdie studie het nuwe insigte gebring in ons verstaan van die verspreiding van polifenole gedurende die produksie van witwyn asook die moontlike impak wat die fenoliese potensiaal van die druiwe en gemoduleerde wynmaak behandelinge op die fenoliese verspreiding en die sensoriese eienskappe van wyn maak.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/106214
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