Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Proteins from various sources, including grape berry cells, yeast, bacteria and fining agents e.g. albumin and casein, have previously been identified in wine. These proteins play various critical roles in the functioning and survival of the organisms that produced them but also exhibit oenological properties, once secreted in the juice/wine. Some of them can indeed be beneficial to winemaking, by releasing aroma compounds from grape-derived precursors, or detrimental to wine quality, by causing protein haze. Yeasts contribute significantly to the protein pool during and after alcoholic fermentation. However, while the extracellular proteins of Saccharomyces cerevisiae, the main wine yeast species, have been characterised, those of non-Saccharomyces yeasts remain largely unknown, especially under winemaking conditions. Although specific extracellular enzymes released by non-Saccharomyces yeasts have been the focus of many studies in recent years, the targeted approaches used have restricted our knowledge to these specific enzymes and excluded the other secreted proteins. A more comprehensive insight into entire secretomes could improve our understanding of how yeasts survive in wine and interact with other species in mixed culture fermentations. This study aims to characterise the exo-proteome of Saccharomyces and selected non-Saccharomyces yeasts in pure and mixed cultures in a wine-like medium. Fermentation kinetics were monitored and the extracellular proteins isolated at the end of fermentation. M. pulcherrima hardly fermented whereas L. thermotolerans fermented slowly but steadily. As expected S. cerevisiae completed the fermentation rapidly. In sequential fermentations, the kinetics resembled those of the non-Saccharomyces yeasts for a period before switching to that of S. cerevisiae. This period varied from 4 to 15 days for M. pulcherrima and L. thermotolerans respectively. Visual observations of the protein content of the medium at the end of fermentation using 1D and 2D SDS-PAGE gels as well as identification of these proteins using mass fingerprinting revealed the large variety of proteins secreted and the influence of yeast interactions on each other’s secretome. The fermentation kinetics observed could partially be explained by the extent of the contribution of the different yeast to the protein content. Proteins secreted by non-Saccharomyces yeasts lowered the potential of wine to form protein haze, with both M. pulcherrima and L. thermotolerans in pure and mixed culture fermentations showing lower haze formation than S. cerevisiae. As far as we know, this is the first report on the secretome of non-Saccharomyces under winemaking condition and the influence non-Saccharomyces proteins have on the protein haze potential of wine, providing the basis for future investigations. / AFRIKAANSE OPSOMMING: Proteïene vanaf verskeie bronne (insluitend druiwe korrels, gis, bakterieë en verhelderings agente bv. albumien en kaseïen) is reeds in wyn identifiseer. Hierdie proteïene speel verskeie rolle in die funksionering en oorlewing van die organismes wat dit produseer, maar beskik ook oor wynkundige eienskappe sodra dit in die sap of wyn uitgeskei word. Hoewel sommige proteïene in wyn wel voordelig mag wees as gevolg van die vrystelling van aroma komponente vanuit druif‐voorlopers, kan dit ook nadelig wees vir wyn kwaliteit deur die troebelheid wat dit kan veroorsaak Gis dra aansienlik by tot die totale proteïen inhoud van wyn, beide gedurende asook na alkoholiese fermentasie. Alhoewel die ekstrasellulêre proteïene van Saccharomyces cerevisiae (die mees algemeen gebruikte gis vir wynmaak) reeds goed gekarakteriseer is, is die proteïene van nie-Saccharomyces giste grootliks onbekend, veral die wat tydens wynmaak vrygestel word. Gedurende die laaste paar jaar het verskeie studies gefokus op spesifieke ekstrasellulêre ensieme wat deur nie-Saccharomyces giste produseer word, maar geteikende benaderings het ons kennis beperk tot net hierdie spesifieke ensieme, en enige ander afgeskeide proteïene uitgesluit. ʼn Meer omvattende insig oor die algehele afgeskeide proteoom kan ons begrip van hoe gis in wyn oorleef en interaksies tussen gis spesies in gemengde kultuur fermentasies verbeter Hierdie studie streef om die sekretoom van Saccharomyces en geselekteerde nie-Saccharomyces giste in suiwer en gemengde kultuur fermentasies van sintetiese wyn medium te karakteriseer. Fermentasie kinetika is gemonitor en die ekstrasellulêre proteïene is teen die einde van fermentasie geïsoleer. Metschnikowia pulcherrima het swak fermenteer terwyl Lachancea thermotolerans stadig tog reëlmatig fermenteer het. Soos verwag, het S. cerevisiae vinnig tot droog fermenteer. In agtereenvolgend geïnokuleerde fermentasies is die kinetika vir ʼn tydperk soortgelyk aan die van die nie-Saccharomyces giste voordat dit oorskakel na die van S. cerevisiae. Hierdie tydperk wissel respektiewelik vanaf 4 tot 15 dae vir M. pulcherrima en L. thermotolerans. Visuele waarnemings van die proteïen-inhoud van die medium aan die einde van die gisting met behulp van 1D en 2D SDS-PAGE gels asook identifisering van hierdie proteïene met behulp van massa vingerafdrukke onthul die groot verskeidenheid proteïene wat afgeskei word, asook die invloed van die giste se interaksies op mekaar se sekretoom. Die fermentasie kinetika waargeneem kan gedeeltelik verklaar word deur die omvang van die bydrae van die verskillende gis tot die proteïen-inhoud. Proteïene wat afgeskei word deur nie-Saccharomyces giste verlaag die potensiaal van wyn om proteïen troebelheid te vorm, met beide M. pulcherrima en L. thermotolerans (in suiwer en gemengde kultuur fermentasies) wat minder troebelheid vorm as fermentasies met S. cerevisiae. Sover ons kennis strek, is hierdie die eerste verslag oor die sekretoom van nie- Saccharomyces onder wynmaak toestande en ook oor die invloed wat nie-Saccharomyces proteïene op die proteïen troebelheid van wyn het, en vorm die basis vir toekomstige navorsing. / Winetech and THRIP

Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The microclimate environment around the bunch is complex. The spatial distribution of leaves as well as bunch position and morphology impact on the path of direct radiation received by the berries. Canopy microclimate is largely determined by the meteorological conditions (air temperature, solar radiation, wind speed and direction, relative humidity, and precipitation) as well as management practices (trellis/training system, canopy height, vine spacing, row orientation, canopy management practices, irrigation and soil variability and management). The fact that the grapevine continuously responds to its environment, adds to the complexity and dynamic nature of the microclimate that the bunches experience. Field studies involving the effect of the natural bunch environment (i.e. light and temperature conditions) on berry composition, are therefore a challenge, due to the difficulties in quantifying meteorological elements such as temperature and light, which can be hugely variable. There are different sensors available to assess bunch and berry temperature and it can be deployed in different ways within the grapevine canopy, but the difficulty remains in studying the variability that exists within a bunch. This study investigated the value of available sensor technology to measure bunch/berry temperature as well as the spatial and temporal variability on a bunch. Differences in temperature on an intra-berry level were assessed whereas the impact of canopy configuration and bunch orientation on the different sensor levels was also investigated. The contribution of macro- and mesoclimate on bunch and berry temperature was addressed by measuring at two locations (Robertson and Stellenbosch). The potential long term differences in temperature within a bunch with regard to thermal accumulation are discussed. Issues around sensor placement and some technical difficulties related to the sensors are discussed. The results indicated how the effects of mesoclimate were transferred through to the different sensors. A dominating effect of the sea breeze in Stellenbosch was found. Canopy configuration/architecture affected the light regime in the canopy, consequently impacting on bunch temperature variability, specifically in Stellenbosch where a "Ballerina" trellising system was used. Bunch orientation resulted in differences in the temporal variability of bunch/berry temperature and little variability was observed in temperature within the berry. Temperatures of berries situated at the back of the bunch were judged more optimal compared to exposed berries. Direct radiation caused extreme temperatures in exposed berries, which may be detrimental to berry composition and wine quality. This emphasized the importance of the canopy (trellis/training system and management practices) in protecting the bunch from extreme conditions. The large on-bunch spatial variability, observed from measurements with the thermal imager, demonstrated the importance of sensor placement in quantifying the bunch temperature regime; this is also relevant for the future development of berry temperature modelling. Thermal accumulation through the season also illustrated the variability that existed within a bunch, suggesting a potential long term effect on the berry composition. This study proved, in conditions similar to those that may prevail in the South African wine industry, that sensor type and positioning need to be carefully considered in any viticultural/oenological study where bunch microclimate and grape temperatures are assessed. / AFRIKAANSE OPSOMMING: Die mikroklimaat omgewing rondom die tros is kompleks. Die ruimtelike verspreiding van blare sowel as trosposisie en -morfologie het 'n impak op die pad waarlangs direkte straling ontvang word deur die korrels. Lowermikroklimaat word grootliks bepaal deur die meteorologiese kondisies (lugtemperatuur, sonstraling, windspoed en -rigting, relatiewe humiditeit en reënval) sowel as bestuurspraktyke (prieel/opleistelsel, lowerhoogte, wingerdstokspasiëring, ry-oriëntasie, lowerbestuurspraktyke, besproeiing asook grondvariasie en bestuur). Die feit dat die wingerdstok voortdurend reageer op sy omgewing dra by tot die kompleksiteit en dinamiese aard van die mikroklimaat wat die trosse ervaar. Veldstudies gemoeid met die effek van die natuurlike trosomgewing (d.w.s. lig- en temperatuurkondisies) op korrelsamestelling is daarom 'n uitdaging. Die rede hiervoor is dat dit problematies is om meteorologiese elemente soos temperatuur en lig, wat baie veranderlik kan wees, te kwantifiseer. Verskillende sensors is beskikbaar waarmee tros- en korreltemperatuur bepaal kan word en dit kan op verskillende wyses binne die wingerdstoklower aangewend word. Die bestudering van die variasie wat bestaan binne 'n tros is egter steeds problematies. Hierdie studie het die waarde ondersoek van die beskikbare sensortegnologie vir die meting van tros/korreltemperatuur en die ruimtelike en tydsvariasie op 'n tros. Verskille in temperatuur op 'n intra-korrelvlak is bepaal terwyl die impak van lowerkonfigurasie en trosoriëntasie op die verskillende sensorvlakke ook ondersoek is. Die bydrae van makro- en mesoklimaat tot tros- en korreltemperatuur is ondersoek deur te meet by twee verskillende liggings (Robertson en Stellenbosch). Die potensiële langtermyn verskille in temperatuur binne-in 'n tros met betrekking tot temperatuur akkumulasie word bespreek. Kwessies rakende sensorplasing en sommige tegniese probleme wat verband hou met sensors word bespreek. Die resultate het aangedui hoedat die effekte van mesoklimaat oorgedra is na die verskillende sensors. 'n Dominerende effek van die seebries is waargeneem in Stellenbosch. Lowerkonfigurasie/argitektuur het die ligregime in die lower beïnvloed en gevolglik 'n invloed gehad op die trostemperatuur veranderlikheid. Dit was veral die geval in Stellenbosch waar 'n "Ballerina" opleistelsel gebruik is. Trosoriëntasie het gelei tot verskille in tydsvariasie van tros/ korreltemperatuur en min variasie is waargeneem in temperatuur binne die korrel. Temperature van korrels wat voorkom aan die agterkant van die tros is beoordeel as meer optimaal vergeleke met blootgestelde korrels. Direkte straling het uiterste temperature in blootgestelde korrels veroorsaak wat nadelig kan wees vir korrelsamestelling en wynkwaliteit. Hierdeur is die belang van die lower (prieel/opleistelsel en bestuurspraktyke) om die tros te beskerm teen uiterste kondisies beklemtoon. Die groot ruimtelike variasie op 'n tros, soos waargeneem in metings met die termiese kamera, het die belangrikheid van sensorplasing in die kwantifisering van die trostemperatuur regime beklemtoon. Dit is ook relevant vir die toekomstige ontwikkeling van korreltemperatuur modellering. Termiese akkumulasie gedurende die seisoen is ook geïllustreer deur die veranderlikheid wat voorkom binne 'n tros, wat dui op 'n potensiële langtermyn effek op die korrelsamestelling. Hierdie studie het bewys, in kondisies wat algemeen voorkom in die Suid-Afrikaanse wynbedryf, dat sensortipe en -plasing sorgvuldig in ag geneem moet word in enige wingerd/wynkundige studie waar trosmikroklimaat en druiftemperature bepaal word. / Winetech and the National Research Foundation for their financial support of the project

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: There is a global demand for technologies to reduce ethanol levels in wine without compromising wine quality. While several chemical and physical methods have been developed to reduce ethanol in finished wine, the target of an industrially applicable biological solution has thus far not been met. Most attempted biological strategies have focused on developing new strains of the main fermentative organism, the yeast Saccharomyces cerevisiae. Gene modification approaches have primarily focused on partially redirecting yeast carbon metabolism away from ethanol production towards glycerol production. These techniques have met with some moderate success, thus the focus of the current study was to re-direct carbon flux towards trehalose production by moderate over-expression of the TPS1 gene. This gene encodes trehalose-6-phosphate synthase, which converts glucose 6-phosphate and UDPglucose to α,α-trehalose 6-phosphate. Previous data have shown that the overproduction of trehalose restricts hexokinase activity reducing the amount of glucose that enters glycolysis. Nevertheless, preliminary TPS1 over-expression studies using multiple copy plasmids have shown some promise, but also indicated significant negative impact on the general fermentation behaviour of strains. In order to reduce such negative impacts of excessive trehalose production, a new strategy consisting in increasing the expression of TPS1 only during specific growth phases and by a relatively minor degree was investigated. Our study employed a lowcopy number episomal vector to drive moderate over-expression of the TPS1 gene in the widely used industrial strain VIN13 at different stages during fermentation. The fermentations were performed in synthetic must with sugar levels representative of those found in real grape must. This, as well as the use of an industrial yeast strain, makes it easier to relate our results to real winemaking conditions. A reduction in fermentation capacity was observed for all transformed strains and controls. Expression profiles suggest that the DUT1 promoter certainly results in increased TPS1 expression (up to 40%) during early exponential growth phase compared to the wild type strain (VIN13). TPS1 expression under the control of the GIP2 promoter region showed increased expression levels during early stationary phase (up to 60%). Chemical analysis of the yeast and the must at the end after fermentation showed an increase in trehalose production =in line with the expression data of TPS1. Importantly, glycerol production was also slightly increased, but without affecting acetic acid levels for the transformed strains. Although ethanol yield is not significantly lower in the DUT1-TPDS1 strain, s statistically significantly lower ethanol yield is observed for over-expression under the GIP2 promotor. Increasing trehalose production during stationary phase appears therefore to be a more promising approach at lowering ethanol yield and redirecting flux away from ethanol production. This controlled, growth phase specific over expression suggests a unique approach of lowering ethanol yield while not impacting on the redox balance. / AFRIKAANSE OPSOMMING: Wêreldwyd is daar ‘n aanvraag na tegnologie wat die etanol vlakke in wyn kan verminder sonder om wyngehalte te benadeel. Terwyl verskeie chemiese en fisiese metodes ontwikkel is om etanol in die finale wynproduk te verminder, is die soeke na 'n industrieel gebaseerde biologiese oplossing tot dusver nie gevind nie. Meeste biologiese strategieë fokus op die ontwikkeling van nuwe rasse van die primêre fermentatiewe organisme, naamlik Saccharomyces cerevisiae. Geen modifikasie benaderings het hoofsaaklik gefokus op die gedeeltelike kanalisering van koolstof metabolisme weg van etanol produksie na gliserol produksie. Hierdie benadering is net matiglik suksesvol, dus is ons huidige fokus om koolstof te kanaliseer na trehalose produksie deur gematigde oor-uitdrukking van die TPS1 geen. Hierdie geen kodeer vir trehalose-6-fosfaat sintase, wat glukose-6-fosfaat en UDP-glukose omskakel na α, α-trehalose-6-fosfaat. Vorige data het getoon dat die oorproduksie van trehalose hexokinase aktiwiteit beperk en die hoeveelheid glukose wat glikolise binne gaan. Voorlopige TPS1 ooruitdrukking studies met behulp van multi-kopie plasmiede toon matige sukses, maar het ook ‘n negatiewe impak op die algemene fermentasie kapasiteit van die gis. Ten einde so 'n negatiewe impak van oormatige trehalose produksie te oorkom, is 'n nuwe strategie gevolg wat bestaan uit die verhoogde uitdrukking van die TPS1 geen slegs gedurende spesifieke groei fases met baie lae vlakke van oor-uitdrukking. Ons studie gebruik 'n lae-kopie episomale vektor met matige oor-uitdrukking van die TPS1 geen in die industriële ras VIN13 op verskillende stadiums tydens fermentasie. Die fermentasie is uitgevoer in sintetiese mos met suiker vlakke verteenwoordigend van dié van werklike wyn mos. Hierdie, sowel as die gebruik van 'n industriële gisras, maak dit makliker om ons resultate te vergelyk met regte wyn fermentasie kondisies. Verlaagde fermentasie kapasiteit is waargeneem vir alle getransformeerde stamme en hul kontroles. Geen uitdrukkings profiele dui op verhoogde TPS1 uitdrukking (tot 40%) onder beheer van die DUT1 promotor gedurende die vroeë eksponensiële groeifase wanneer vergelyk word met die wilde tiepe (VIN13). TPS1 uitdrukking onder die beheer van die GIP2 promotor het verhoogde uitdrukking van tot 60% gedurende die vroeë stasionêre fase. Chemiese analise van die gis aan die einde van fermentasie dui op ‘n toename in trehalose produksie wat korreleer met die uitdrukking profiele van TPS1. Gliserol produksie is ook effens verhoog, maar sonder ‘n toename in asynsuur vlakke vir die getransformeerde rasse. Alhoewel etanol opbrengs nie aansienlik laer vir die DUT1-TPS1 ras is nie, is etanol opbrengs vir die oor-uitdrukking onder beheer van die GIP2 promotor wel laer. Toenemende trehalose produksie gedurende stasionêre fase blyk dus 'n meer belowende benadering op die verlaging van etanol opbrengs en her-kanaliseering weg van etanol produksie. Hierdie benadering met die fokus op groeifase spesifieke oor-uitdrukking dui op 'n unieke strategie vir die verlaging van etanol opbrengs sonder om die redoks balans te beinvloed. / The NRF, IWBT and Stellenbosch University for funding

Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Acids are one of the major components that originate largely from the berry, that are found in wine, and that influence the sensory perception. The presence of organic acids in adequate concentrations in the grape berry, of which tartaric- and malic acid are the main organic acids present, is important as this determines the potential of a must to produce a good and stable wine. The effect of temperature on the organic acid content of the must is widely discussed with higher temperatures in general being associated with lower quantities of organic acids present in the juice, and lower temperatures during ripening associated with higher quantities, specifically in the case of malic acid. Due to the topographical diversity of the Stellenbosch Wine of Origin district and the closeness of the ocean and the occurrence of sea breezes, the mesoclimate differs greatly over short distances. Sixteen sites, consisting of eight Sauvignon Blanc and Cabernet Sauvignon sites respectively, were selected from a broader terroir study site network. Three vintages with complete climatic datasets were selected for vintage comparisons. Climate in the study area was monitored on differing scales, and data from a weather station network, as well as from mesoclimatic dataloggers within the sites were available. The available data was firstly compared to determine the variability of the data, not only between the two climatic scales, but also between the sites. Different climate classification indices and parameters available in literature were thereafter compared and evaluated for the best representation in this area. The Huglin index was found to be a better representation regarding the thermal climatic indices. Due to the great differences between temperatures noted for the mesoclimatic loggers and the nearest automatic weather station, the use of mesoclimatic logger data was preferred, and is advised in future studies where this scale of data is available. Malic and tartaric acid has a definite synthesis period up until véraison, after which the content of tartaric acid remains constant in the berry and the content of malic acid decreases until harvest due to mainly respiration. The temperature data was therefore separated in a synthesis period from flowering to véraison, and a ripening period from véraison to harvest. In this study, clear differences were firstly seen in the climate as expected, not only between sites per vintage, but in addition between vintages and between vintages per site. The phenological differences between the sites could be largely attributed to the differences in temperature as phenology and temperature was found to be highly correlated in this study. Differences in the ripening parameters were noticed in addition to the contents of the organic acids between sites, although no definite contribution of temperature was shown to affect the contents of these compounds at either véraison or harvest. These differences may be attributed to other factors such as the soil water content and the canopy architecture. In addition, these factors all contribute in differing percentages to the differences found in the contents per site. It was found though that temperature can be used as an indicator of the organic acid content in the grape berry, considering that the temperature data is available on a mesoclimatic scale, separated in a synthesis and period of degradation, and the number of hours within the temperature thresholds are determined. Differences seen in the organic acid contents can however not only be attributed to the differences in topography and the temperature as discussed in this study. / AFRIKAANSE OPSOMMING: Sure is belangrike druifkomponente wat grootliks hul oorsprong in die korrel het, in die wyn voorkom, en die sensoriese persepsie van die wyn beïnvloed. Die voorkoms van organiese sure in genoegsame konsentrasies in die korrel, waarvan wynsteensuur en appelsuur die hoof organiese sure is, is belangrik aangesien dit die potensiaal van die sap om ʼn goeie en stabiele wyn te produseer, bepaal. Hoe temperatuur die inhoud van organiese sure in die druiwesap affekteer is gereeld onder bespreking, met hoër temperature in die algemeen geassosieer met ʼn laer inhoud van organiese sure, terwyl laer temperature geassosieer word met ʼn hoër inhoud van organiese sure in die sap, veral in die geval van appelsuur. As gevolg van die topografiese diversiteit van die Stellenbosch Wyn van Oorsprong distrik, asook die nabyheid van die oseaan met die gepaardgaande voorkoms van die seebries, verander die mesoklimaat aansienlik oor klein afstande in hierdie area. Vir die studie was sestien wingerde, wat bestaan het uit agt Sauvignon Blanc en agt Cabernet Sauvignon wingerde, geselekteer vanuit ʼn groter terroir studie. Verder was drie seisoene, met volledige klimaatsdatastelle, geselekteer vir die vergelyking van data tussen die seisoene. Klimaat was op verskillende skale binne die studie area gemonitor en data van ʼn weerstasie netwerk, sowel as van mesoklimaat dataversamelaars binne die wingerde, was beskikbaar. Die beskikbare datastelle was vergelyk, asook geëvalueer, om die mees verteenwoordigende datastel vir die area te bepaal. Met die oorweging van die termiese indekse was daar gevind dat die Huglin indeks beter verteenwoordigend van die area was. Verder, as gevolg van die groot verskille wat gevind is tussen die temperature gemeet met die mesoklimaat dataversamelaars en die naaste outomatiese weerstasie, was daar besluit dat die gebruik van die mesoklimaat data verkies is en is dit ook aan te beveel vir die gebruik in toekomstige navorsing indien die tipe data beskikbaar is. Wynsteen- en appelsuur het beide ʼn definitiewe sintese periode tot en met véraison, waarna die hoeveelheid wynsteensuur in die korrel relatief konstant bly en die hoeveelheid appelsuur afneem hoofsaaklik as gevolg van respirasie. Die temperatuur data was dus verdeel in ‘n periode van sintese vanaf blom tot en met véraison, en ʼn rypwordingsperiode vanaf véraison tot en met oes. In hierdie studie was daar eerstens groot verskille waargeneem in die klimaat soos wat daar verwag is. Hierdie verskille was nie net waargeneem as tussen die seisoene nie, maar ook tussen die wingerde binne ʼn seisoen. Die fenologiese veskille tussen die wingerde wat ook waargeneem is, kon hoofsaaklik aan die verskille in die temperatuur toegeskryf word en ʼn goeie korrelasie tussen temperatuur en fenologie is opgemerk. Merkwaardige verskille in die rypwordingsparameters, asook in die inhoud van die organiese sure, was waargeneem, alhoewel die bydrae van temperatuur op die inhoud van hierdie komponente by véraison of oes nie as definitief getoon is nie. Dit kan toegeskryf word aan die bydrae van ander faktore, soos byvoorbeeld die grondwaterinhoud en die lowerargitektuur, op die inhoud van hierdie komponente. Die addisionele faktore dra egter in verskillende persentasies by tot die verskille waargeneem tussen die wingerde.

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Non-Saccharomyces yeasts of oenological origin have previously been associated with spoilage or regarded as undesired yeasts in wine. However, these yeasts have recently come under investigation for their positive contribution towards wine aroma especially when used in sequential or co-inoculated fermentations with Saccharomyces cerevisiae. These yeasts are also known to secrete a number of enzymes that could be applicable in wine biotechnology. Amongst these enzymes are aspartic proteases. The secreted proteases from some non-Saccharomyces yeast may play a role in protein haze reduction, as demonstrated by some authors, while simultaneously increasing the assimilable nitrogen content of the wine for the utilization and growth of fermentative microorganisms. Moreover, the proteases may have an indirect effect on wine aroma by liberating amino acids that serve as aroma precursors. Although many screenings have been performed detecting protease activity in non-Saccharomyces yeasts, no attempts have been made to characterize these enzymes. This study set out to isolate and characterize genes encoding extracellular aspartic proteases from non-Saccharomyces yeasts. An enzymatic activity screening of a collection of 308 Saccharomyces and non-Saccharomyces yeasts, isolated from grape must, was performed. The aspartic protease-encoding genes of two non- Saccharomyces yeasts, which showed strong extracellular proteolytic activity on plate assays, were isolated and characterized by in silico analysis. The genes were isolated by employing degenerate and inverse PCR. One gene was isolated from Metschnikowia pulcherrima IWBT Y1123 and named MpAPr1. The other putative gene was isolated from Candida apicola IWBT Y1384 and named CaAPr1. The MpAPr1 gene is 1137 bp long, encoding a 378 amino acid putative protein with a predicted molecular weight of 40.1 kDa. The CaAPr1 putative gene is 1101 bp long and encodes a 367 amino acid putative protein with a predicted molecular weight of 39 kDa. These features are typical of extracellular aspartic proteases. The deduced protein sequences showed less than 40% homology to other yeast extracellular aspartic proteases. By heterologous expression of MpAPr1 in S. cerevisiae, it was confirmed that the gene encodes an extracellular acid protease. The expression of MpAPr1 was shown to be induced in media containing proteins as sole nitrogen source and repressed when a preferred nitrogen source was available. The gene was expressed in the presence of casein, bovine serum albumin (BSA) and grape juice proteins and repressed in the presence of ammonium sulphate. Expression was most induced in the presence of grape juice proteins, which was expected since these proteins are present in the natural habitat of the yeast. A genetic screening confirmed the presence of the MpAPr1 gene in 12 other M. pulcherrima strains isolated from grape juice. The extracellular protease activity of the strains was also visualized on plates. As far as we know, this is the first report on the genetic characterization of secreted aspartic proteases from non-Saccharomyces yeasts isolated from grape must and provides the groundwork for further investigations. / AFRIKAANSE OPSOMMING: Nie-Saccharomyces giste is voorheen met wynbederf geassosieer en hul teenwoordigheid in wyn is ongewens. Hierdie giste is onlangs ondersoek vir hulle positiewe bydrae tot wyn aroma, in veral sekwensiële en ko-inokulerings met Saccharomyces cerevisiae. Sommige van die nie-Saccahromyces giste skei ‘n verskeidenhied ensieme af wat moontlik vir die wynmaker van nut kan wees. Een groep van hierdie ensieme is die aspartiese suurproteases. Soos deur sommige navorsers aangetoon word, kan die proteases die vorming van proteïenwaasverlaging, terwyl dit terselfdertyd die assimilerende stikstofinhoud van die wyn vir die gebruik en groei van fermentasie-mikroörganismes verhoog. Die proteases kan moontlik ook ‘n indirekte uitwerking op die aromaprofiel van die wyn hê deur die vrystelling van aminosure wat as aromavoorlopers dien. Alhoewel baie studies gedoen is wat die ekstrasellulêre teenwoordigheid van proteases bevestig in nie-Saccharomyces giste wat van druiwesap/wyn afkoms is, is daar geen dokumentasie oor die genetiese karakterisering van hierdie ensieme beskikbaar nie. Die doel van hierdie studie was om gene wat aspartiese proteases in nie-Saccharomyces giste enkodeer, te isoleer en gedeeltelik te karakteriseer. ‘n Versameling van 308 Saccharomyces en nie-Saccharomyces giste wat uit druiwe sap geïsoleer is, is gesif vir ensiematiese aktiwiteit deur plaattoetse uit te voer. Twee gene wat aspartiese protease enkodeer, is geïsoleer van twee nie-Saccharomyces giste. Dit hetpositief gedurende die aktiwiteitstoetse getoets en is deur in silico–analise gekarakteriseer. Die gene is deur die uitvoering van gedegenereerde en inverse PKR geïdentifiseer. Een geen is vanaf Metschnikowia pulcherrima IWBT Y1123 geïsoleer en is MpAPr1 genoem, terwyl die ander van Candida apicola IWBT Y1384 geïsoleer en CaAPr1 genoem is. Die MpAPr1-geen is 1137 bp lank en enkodeer ‘n proteïen wat uit 378 aminosure bestaan met ‘n voorspelde molekulêre massa van 40.1 kDa. Daar teenoor is die CaAPr1-geen 1101 bp lank en enkodeer vir ‘n proteïen wat uit 367 aminosure met ‘n molekulêre massa van 39 kDa bestaan. Hierdie eienskappe is kenmerkend van aspartiese protease. Die afgeleide proteïenvolgorde het minder as 40% homologie met ander ekstrasellulêre aspartiese proteases vertoon, wat dui op die nuwigheid van hierdie ensieme. Die MpAPr1-geen is heterologies in S. cerevisiae YHUM272 uitgedruk en dit het bevestig dat die geen inderdaad ‘n ekstrasellulêre aspartiese protease enkodeer. Die MpAPr1-geen is uitgedruk in media wat alleenlik proteïen as stikstofbron bevat het, terwyl dit onderdruk is in gevalle waar ‘n verkose stikstofbron beskikbaar was. Die geen is uitgedruk in die teenwoordigheid van kaseïen, BSA en proteïene afkomstig vanaf druiwesap en in die teenwoordigheid van ammoniumsulfaat onderdruk. Die hoogste uitdrukking was in die teenwoordigheid van druifproteïene. Hierdie proteïene is teenwoordig in die natuurlike habitat van die gis en is dus dalk ‘n bekende stikstofbron vir die gis. ‘n Genetiese sifting het die teenwoordigheid van die MpAPr1-geen in 12 ander M. pulcherrima–rasse, wat ook van wynkundige oorsprong is, bevestig. Die aspartiese protease-aktiwiteit van die 12 rasse is ook op agarplate waargeneem. Na ons wete, is dit die eerste verslag oor die genetiese karakterisering van afgeskeide aspartiese proteases van nie- Saccharomyces giste van wynkundige oorsprong en verskaf die grondslag vir verdere ondersoek.

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Yeast strains contend with numerous stresses during winemaking. An inability to perceive and initiate the physiological changes needed to adapt to stress, has been linked to slow or incomplete (residual sugar > 4 g/L) fermentations. Wine yeast strains differ in genotype; this is manifested as differences in their stress tolerance, and fermentation performance. The first goal of this study was to evaluate how the initial sugar (200 or 240 g/L) and nitrogen (50, 100, 250, or 400 mg/L) content, and the fermentation temperature (15°C or 20°C) affected the fermentation performance of 17 commercial wine yeast strains. Fermentation performance was evaluated based on the fermentation kinetics (lag phase, maximum fermentation rate and total weight loss by CO2 evolution), residual sugar content and yeast dry weight. The results demonstrate that the fermentation performances of commercial yeast cultures are significantly and differently affected by initial nitrogen and sugar levels, as well as the fermentation temperature. Additionally, excess nitrogen had a negative impact on the fermentation kinetics and sugar consumption. Nitrogen deficiency is a common cause of slow and incomplete fermentations, as it affects yeast growth and thus fermentation rates. Nitrogen supplements are routinely added at the onset of fermentation, reducing the risk of problematic fermentations. Therefore characterising the fermentative ability of a strain over a range of oenologically relevant conditions, could aid winemakers in selecting a yeast strain capable of fermenting a grape must (of known sugar and nitrogen levels) to completion at the desired fermentation temperature. Investigations on fermentation related stress generally focus on its influence on fermentation rate and sugar consumption. However, from a winemaking perspective, the strain’s ability to produce the desired volatile aroma compounds is equally important. Yet, literature provides little insight into the influence stress has on the volatile aroma profile; this is surprising as wine aroma is closely linked to wine quality and consumer liking. The final goal of this study was to evaluate changes to the volatile aroma profiles produced by five commercial yeast strains, in response to hyperosmotic and temperature stress. The concentrations of the aroma compounds were quantified using a gas chromatograph coupled to a flame ionization detector. The results show that hyperosmotic and temperature stress caused significant changes in the levels of a number of aroma compounds. Furthermore, the changes observed differed among the evaluated strains, as well as for the fermentation stress treatments studied. Future aims should be directed towards the potential application of yeast strain selection as a means to avoid problematic fermentations in grape must; in addition to the further characterisation of the relationship between stress and the resultant volatile aroma profile in wine. / AFRIKAANSE OPSOMMING: Gisrasse moet verskeie stresfaktore afweer tydens die wynmaak proses. Die onvermoë van ‘n wyngis om stres waar te neem en die nodige fisiologiese veranderinge te inisieer om aan te pas by die strestoestande word met slepende of onvolledige fermentasies (met ‘n residuele suiker van meer as 4 g/L) geassosieer. Wyngisrasse verkil in genotipe; wat as groot verskille in die graad van strestoleransie, en dus ook fermentasie sukses geopenbaar word. Die eerste doelwit van hierdie studie was om te evalueer hoe die suiker (200 of 240 g/L) en stikstof (50, 100, 250, of 400 mg/L), asook die fermentasie temperatuur (15°C of 20°C) die fermentasie prestasie van 17 kommersiële wyngiskulture beïnvloed. Die sukses van fermentasie is geëvalueer op grond van fermentasie kinetika (sloerfase, maksimum fermentasiespoed en totale gewigsverlies as CO2 verlies), die residuele suiker inhoud en die gis droë massa. Die resultate demonstreer dat die fermentasie sukses van kommersiële giskulture beduidend en verskillend beïnvloed word deur die aanvangsstikstof en – suikerkonsentrasies, asook die fermentasie temperatuur. Daarbenewens, wanneer stikstof in oormaat teenwoordig is kan dit ‘n negatiewe impak op fermentasietempo en suiker metabolisme hê. Beperkende vlakke van stikstof ‘n algemene oorsaak van slepende of onvolledige fermentasies, aangesien stikstof die groei en gevolglik ook die fermentasiespoed van gis beïnvloed. Stikstofaanvullings word dikwels tot druiwemos toegevoeg aan die begin van gisting, wat die risiko van probleemfermentasies verlaag. Dus kan die karakterisering van die fermentasievermoë van ‘n gisras vir ‘n reeks wynkundig relevante kondisies die wynmaker help om ‘n gisras te selekteer wat in staat is om ‘n druiwemos (waarvan die suiker en stikstofvlakke bekend is) droog te gis by die gewenste temperatuur. Meeste studies wat fermentasieverwante stress ondersoek, fokus op die die invloed daarvan op fermentasietempo en suikerverbruik. Van ‘n wynmaakperspektief is die gis se vermoë om die gewensde vlugtige aroma komponente te produseer egter ewe belangrik as die vermoë om fermentasie te voltooi. Tog verskaf die literatuur min insig tot die invloed van stres op die vlugtige aromaprofiel; wat verbasend is aangesien die aromaprofiel ‘n belangrike faktor is van die waargenome wynkwaliteit en daarom ook verbruikersvoorkeur. Die finale doelwit van hierdie projek was om die veranderinge tot die vlugtige aromaprofiel geproduseer deur vyf kommersiële gisrasse in reaksie op hiperosmotiese stres en temperatuur stres te evalueer. Die konsentrasies van die aromakomponente is gekwantifiseer deur gas chromatografie gekoppel aan vlam‐ioniserende deteksie. Die resultate wys dat hiperosmotiese‐ en temperatuur stres beduidende veranderinge meebring in die vlakke van ‘n aantal aromakomponente. Verder is die waargenome veranderinge ook verskillend vir die geëvalueerde gisrasse, asook vir die verskille stresbehandelings wat ondersoek is. Toekomstige studies behoort gerig te wees op die toepassing van gis seleksie om potensiële probleemfermentasies in druiwemos te voorkom; asook die verdere karakterisering van die verhouding tussen omgewingstresfaktore en die gevolglike vlugtige aromaprofiel in wyn.

Thesis (MSc)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: Wine is a complex medium. Wine aroma, flavour and colour are important quality factors, but these can be influenced by many factors, such as grape-derived compounds that exist as free volatiles and also as glycosidically bound. The chemical composition of wine is determined by factors such as grape variety, geographic position, viticulture condition, microbial ecology of the grape and the winemaking process. The varietals aroma is determined by both the volatile and the non-volatile compounds, such as monoterpenes, norisoprenoids and benzene derivatives, which are naturally present in the wine. Monoterpenes are very important in the flavour and aroma of grapes and wine. They can be found in grapes and wine either in the free, volatile and odorous form, or in the glycosidically-bound, non-volatile and non-odorous form. The ratio of glycosidically-bound compounds to free aroma compounds is very high in the Gewürztraminer, Muscat and Riesling cultivars in particular. The glycosidic bonds can be hydrolysed either by the acid method or by using enzymes. The acid method is disadvantageous because it can modify the monoterpenes, whereas enzymatic hydrolysis has the advantage of not modifying the aroma character. The enzyme method of breaking the glycosidic bonds occurs in two successive steps: initial separation of glucose from the terminal sugar by a hydrolase (a-L-arabinofuranosidase, a-L-rhamnosidase or β-apiosidase, depending on the aglycone moiety), followed by the breaking of the bond between the aglycone and glucose by β-glucosidase. The enzyme β-glucosidase can be obtained from many plant (Vitis vinifera), bacterial, yeast or fungal sources. Most of the enzymes produced by these sources are not functional under the winemaking conditions of low pH, low temperature, high glucose and high ethanol content. However, β-glucosidases from fungal origins, particularly from Aspergillus spp., are tolerant of winemaking conditions. The idea of using the β-glucosidase gene from the fungus Aspergillus kawachii (BGLA), which is linked to the cell wall and the free β-glucosidase, was to determine if anchoring the enzyme to the cell wall will increase the activity of the enzyme compared to the free enzyme. Four plasmids, pCEL 16, pCEL 24, pDLG 97 and pDLG 98, were used in this study. BGLA that was cloned into the plasmids pCEL 24 and pDLG 97 was linked to CWP2, and in pDLG 98 it was linked to AGa1 anchor domains. All the plasmids were genome-integrated and expressed in the reference strain Saccharomyces cerevisiae 303-1A. All the transformants were grown in 2% cellobiose and showed higher biomass production compared to the reference strain. β-Glucosidase activity was also assayed and transformed strain W16 showed a fourfold increase in activity compared to the reference strain. There was no significant increase in the activity of the other transformed strains, W24, W97 and W98. Enzymatic characterisation for optimum pH and temperature was done – for all strains the optimum pH was 4 and the optimum temperature was 40ºC. The recombinant strains together with the reference strain were used to make wine from Gewürztraminer grapes. The levels of numerous monoterpenes were enhanced in the resultant wines. The concentration of nerol was increased fourfold, that of citronellol twofold, and geraniol was 20% higher than in the wild type. There was also an increase in the levels of linalool and a-terpinol, but this was not significant. In wines produced with W97, W98 and W24, monoterpene levels did not show a significant difference. In future, the expression of the W16 expression cassette in an industrial wine yeast strain could be performed. In combination with the production of enzymes such as a-arabinofuranosidase, a-rhamnosidase and β-apiosidase, which are involved in the first step of enzymatic hydrolysis, this wine strain could release the bound monoterpenes and enhance the aroma of the wine. / AFRIKAANSE OPSOMMING: Wyn is ‘n komplekse medium. Wynaroma, -geur en -kleur is belangrike kwaliteitsfaktore, hoewel hierdie kwaliteite deur verskeie faktore beïnvloed kan word, soos druifafgeleide verbindings wat as vry vlugtige stowwe teenwoordig kan wees of glikosidies gebind is. Die chemiese samestelling van wyn word bepaal deur faktore soos druifvariëteit, geografiese ligging, wingerdkundige toestande, mikrobiese ekologie van die druif en die wynbereidingsproses. Die variëteitsaroma word bepaal deur vlugtige en nie-vlugtige verbindings, soos monoterpene, norisoprenoïede en benseenderivate, wat natuurlik in die wyn voorkom. Monoterpene is baie belangrik vir die geur en aroma van druiwe en wyn. Monoterpene is teenwoordig in die druiwe en wyn in vry, vlugtige en geurige, of in glikosidiesgebinde, nie-vlugtige en nie-geurige vorms. Die verhouding van glikosidiesgebonde verbindings tot vry aromaverbindings is baie hoog, veral in die Gewürztraminer-, Muscat- en Riesling-kultivars. Glikosidiese verbindings kan deur óf die suurmetode óf die ensiemmetode gehidroliseer word. Die nadeel van die suurmetode is dat dit monoterpene kan modifiseer, terwyl die ensiemmetode die voordeel het dat dit nie die aromakarakter modifiseer nie. Die ensiemmetode waarmee die glikosidiese verbinding afgebreek word, vind in twee opeenvolgende stappe plaas: aanvanklike skeiding van glukose van die terminale suiker deur ‘n hidrolase (a-L-arabinofuranosidase, a-Lramnosidase of β-apiosidase, afhangende van die aglikoongedeelte), gevolg deur die verbreking van die verbinding tussen die aglikoon en glukose deur β- glukosidase. Die β-glukosidase-ensiem kan vanaf ‘n verskeidenheid plant- (Vitis vinifera), bakterie-, gis- en swambronne verkry word. Die meerderheid van die ensieme wat deur hierdie bronne geproduseer word, is nie onder die wynbereidingstoestande van lae pH, hoë temperatuur, hoë glukose en hoë etanol funksioneel nie. β- Glukosidase vanaf ‘n swamoorsprong, veral vanaf Aspergillus-spesies, kan egter wynbereidingstoestande verdra. Die idee agter die gebruik van die β-glukosidasegeen afkomstig van die swam Aspergillus kawachii (BGLA), wat aan die selwand en die vry β-glukosidase gekoppel is, was om te bepaal of die aktiwiteit van die ensiem in vergelyking met dié van die vry ensiem verhoog sou word indien die ensiem aan die selwand geanker is. Vier plasmiede, pCEL 16, pCEL 24, pDLG 97 en pDLG 98, is in hierdie studie gebruik. BGLA, wat in die plasmiede pCEL 24 en pDLG 97 gekloneer is, is gekoppel aan CWP2, en in pDLG 98 is dit aan AGa1-ankergebiede gekoppel. Al die plasmiede is in verwysingsras Saccharomyces cerevisiae 303-1A genoomgeïntegreer en uitgedruk. Al die transformante is in 2% sellobiose gegroei en het hoër biomassaproduksie as die verwysingsras getoon. β-Glukosidaseaktiwiteit is ook geëssaieer en die getransformeerde ras W16 het ‘n viervoudige verhoging in aktiwiteit in vergelyking met die verwysingsras getoon. Daar was geen noemenswaardige verhoging in die aktiwiteit van die ander getransformeerde rasse, W24, W97 en W98, nie. Ensimatiese karakterisering vir optimum-pH en - temperatuur is gedoen – vir al die rasse was die optimum-pH 4 en die optimumtemperatuur 40ºC. Die rekombinante rasse, tesame met die verwysingsras, is gebruik om wyn met Gewürtztraminer-druiwe te maak. Die vlakke van talryke monoterpene is in die gevolglike wyne verhoog. Die konsentrasie van nerol is viervoudig verhoog, dié van sitronellol tweevoudig, en geraniol was 20% hoër as in die wilde tipe. Daar was ook ‘n verhoging in die vlakke van linaloöl en a-terpinol, maar hierdie verhoging was nie noemenswaardig nie. In wyne wat met W97, W98 en W24 gemaak is, het die monoterpeenvlakke nie ‘n noemenswaardige verskil getoon nie. In die toekoms sal die uitdrukking van die W16-uitdrukkingskasset in ‘n industriële wyngisras uitgevoer kan word. In kombinasie met die produksie van ensieme soos a-arabinofuranosidase, a-ramnosidase, β-apiosidase, wat in die eerste stap van ensimatiese hidrolise betrokke is, sal hierdie wyngisras die gebonde monoterpene kan vrylaat en die aroma van die wyn kan verbeter.

Thesis (MSc)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The importance of indigenous fruit wines is not well researched and documented. There is a need to develop and exploit these valuable food resources through improved production practices, storage, preservation and utilization technologies. The maruia fruit is beneficial in many ways, it can be used for making juice, jam, beer or can be eaten as a whole fruit. The highly nutritive nature of the fruit, its distinctive tropical flavor, its wild occurrence and demand by the local and international communities for the by-products of the fruit necessitated efforts to optimize the technological processes for the production of the possible by-products. This study focuses on the fermentation technology of the maruia fruit. The effect of enzymes prior to the fermentation process and post-fermentation was evaluated. For pre-fermentation processes we focused on the ability of commercial enzymes to increase juice yield, improve the clarification and filterability. For pre- and post-fermentation applications, aroma release was considered. The results indicated a significant increase in the yield depending on the enzyme used. An increase of at least 2% was recorded and a maximum of 12% yield increase was observed. The enzymes also had a phenomenal effect on the release of bound monoterpenes and hence enhancing the flavor of the juice. The panel of judges confirmed the results from the gas chromatography analyses by noting an increase in flavor intensity in the enzyme treated juice. The possibility of selecting a yeast strain that performs best during the fermentation of maruia pulp was also looked at. This study aimed at selecting a strain that produces wine and distillate with the typical maruia flavor complex. We showed the effect of the different yeast strains, in the wines and distillates, on the principal volatile compounds. We then correlated the performance of the different strains as perceived by the panel to the various volatile compounds. The effect of fermentation temperature on the performance of the different yeast strains was also considered. Fermenting the maruia pulp at different temperatures resulted in the production of wines and distillates with different volatile profiles for the different yeast strains. The wines and distillates fermented at a low temperature of 15°C were preferred to the wines and distillates fermented at 30°C. However, not all strains performed well at 15°C, strains like NT116 performed better at 30°C. The different commercial strains produced wines and distillates with significantly different flavor profiles. These differences in the flavor profiles were reflected in the sensory evaluation where, depending on the interaction of the volatile compounds some wines and distillates were preferred to others. The effect of the different commercial enzymes and yeast strains should thereof be further evaluated and optimized on a larger scale. This would greatly help prevent variation in quality of the fermented by-products of the maruia fruit. / AFRIKAANSE OPSOMMING: Die belang van inheemse vrugtewyne is nie goed nagevors en gedokumenteer nie. Daar is 'n behoefte om hierdie waardevolle voedselbronne te ontwikkel en te benut, deur verbeterde produksiepraktyke, storing, preservering en benuttingstegnologieë. Die maroelavrug is veelsydig op baie wyses, deurdat dit gebruik word vir die maak van sap, konfyt, bier, of as heel vrug geëet kan word. Die vrug is hoog in voedingswaarde, het In kenmerkende tropiese geur, kom wild voor, en is in aanvraag by plaaslike en internasionale gemeenskappe vir die by-produkte van die vrug. Dit maak dit essensieel om die tegnologiese prosesse vir die produksie van hierdie moontlike by-produkte te optimiseer. Hierdie studie fokus op die fermentasie-tegnologie van die maroelavrug. Die effek van ensieme voor en na die fermentasie-proses is geëvalueer. Vir prosesse wat voor fermentasie plaasvind, het ons gefokus op die vermoë van kommersiële ensieme om sapopbrengs te verhoog, asook om verheldering en filtrering te verbeter. Vir beide voor- en na-fermentasie toepassings is die vrystelling van aroma gemonitor. Die resultate dui op 'n betekenisvolle verhoging in die sapopbrengs, afhangende van die ensiem wat gebruik is. 'n Verhoging van ten minste 2% is opgeteken, en 'n maksimum van 12% opbrengsverhoging is waargeneem. Die ensieme het ook 'n geweldige effek op die vrystelling van gebonde monoterpene gehad, en dus die verhoging in die geur van die sap. Die proepaneel het die resultate bevestig van die gaschromatografie-analises, deur 'n verhoging in die geurintensiteit in die ensiembehandelde sap te bemerk. Daar is ook gekyk na die moontlikheid om 'n gisras te selekteer wat die beste presteer tydens die fermentasie van maroela-pulp. Hierdie studie het die doelstelling gehad om In gisras te selekteer wat wyn en distillaat produseer met In tipiese maroelageurkompleks. Ons het die effek van verskillende gisrasse aangedui in die wyne en distillate, op grond van van vlugtige komponente. Ons het dan die prestasie van die verskillende rasse, soos waargeneem deur die paneel, gekorrelleer met die verskeie vlugtige komponente. Die effek van fermentasie-temperatuur op die werkverrigting van die verskillende gisrasse is ook in ag geneem. Fermentasie van die maroela-pulp by verskillende temperature het gelei tot die produksie van wyne en distillate met verskillende vlugtige profiele vir die verskillende gisrasse. Die wyne en distillate wat by In laer temperatuur van 15°C gefermenteer is, is verkies bo die wyne en distillate wat by 30°C gefermenteer is. Alle rasse het egter nie baie goed presteer by 15°C nie, soos byvoorbeeld NT116 wat beter presteer het by 30°C. Die verskillende kommersiële rasse het wyne en distillate geproduseer met betekenisvol verskillende geurprofiele. Hierdie verskille in geurprofiele is gereflekteer in die sensoriese evaluering waar, afhangende van die interaksie van die vlugtige komponente, sommige wyne en distillate bo ander verkies is. Die effek van die verskillende kommersiële ensieme en gisrasse moet verkieslik verder op groter skaal geëvalueer en geoptimiseer word. Dit sal veral help om variasie in kwaliteit van die gefermenteerde by-produkte van die maroelavrug te voorkom.

published_or_final_version / Business Administration / Master / Master of Business Administration

The use of wine as a medicine is not a new idea, but one that has been rediscovered and given credibility due to current research findings. This research examines the use of wine as a medicine in the past and currently. The whole question of wine and health is put into a more balanced and proper perspective, instead of the ill-informed, negative anti-alcohol view. The aim of the thesis is to document the history of the uses of wine as a medicine, particularly in Australia. The author uses a social ecology framework,which is concerned with the interrelationships between the domains of the personal, social and environmental, with a critical, holistic transdisciplinary understanding approach. One aim of the research is to change the perception of wine from one of a drink for special occasions to one of a daily health drink taken in moderation with a meal / Doctor of Philosophy (PhD)