Thesis--Universität Zürich. / Vita. "Erscheint als Heft 2, Band 19 der Schweizer Studien zur Geschichtswissenschaft." Bibliography: p. 104-106.

Thesis (MSc(Agric))--University of Stellenbosch, 2005. / Bibliography. Also available via the Internet.

Thesis (MAgric)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

Bibliography: leaves 200-214. Three structurally related compounds, 2-acetyltetrahydropyridine (ACTPY), 2-ethyltetrahydropyridine (ETPY) and N-heterocycle, 2-acetyl-1-pyrroline (ACPY), were quantified and found to be unique components of mousy wines. 35 lactic acid bacteria (LAB) were screened for the ability to produce mousy off-flavour. In addition to Lactobacillus brevis and L. cellobiosus, a diversity of LAB species, particularly heterofermentative Lactobacillus spp. and Oenococcus oeni exhibited this ability in a range of ethanolic and wine-based media. The substrates and metabolism of mousy compound formation by LAB were also investigated. A pathway for the formation of ACPY and ACTPY by heterofermentative LAB was proposed.

No description available.

No description available.

Master of Science

Wines are composed of numerous compounds that are complex, making them difficult to analyze. Wine evaluation and discrimination is typically done through chemical and human sensory evaluation. Unfortunately, both of these methods are time consuming and expensive. Therefore a new rapid analysis technique for wine discrimination and analysis is desired. The electronic nose has been suggested as an alternative to current wine discrimination techniques. In this study, a quartz microbalance-based electronic nose system was utilized to analyze the overall volatile components of wine. The electronic nose was optimized for Cabernet Sauvignon and Mouvèdre wine to gain maximum sensor response from the sensors. Response surface methodology was used to determine the optimum sensor response by varying three experimental parameters: sensor temperature, sample temperature and equilibrium time. The maximum sensor response occurred at an equilibrium time of 20 min for each varietal and at a sample temperature of 55ºC and 56ºC for Cabernet Sauvignon and Mouvèdre, respectively. The optimum sensor temperature selected for this study was 40ºC for both varietals. Using the optimum sensor settings, the electronic nose was used to analyze Cabernet Sauvignon wines. Grapes were treated with ethanol spray (5%, and 10%) 13 weeks post-bloom, which has been shown to affect the overall quality of the final wine product. Wine samples were evaluated using chemical analyses, human sensory evaluation and electronic nose. Significant differences between the wines were observed based on pH, percent alcohol, and color intensity only. A consumer sensory panel consisting of 81 panelists was unable to differentiate amongst sample treatments. However, the electronic nose was able to differentiate between the control group and the treated samples 100% of the time. Canonical discriminant analysis of the data placed the 5% ethanol treatment as a sub-set of the 10% ethanol treatment. The results indicate that the electronic nose can be used as a discriminatory tool for assessing wines. / Master of Science

Thesis (MSc)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Monoterpene alcohols (monoterpenols) play an important role in the flavour and aroma of grapes and wine. This is especially applicable to wines of a muscat variety, but these flavour compounds are also present in other non-muscat grape varieties, where they supplement other varietal flavours and aromas. These monoterpenols can be found in grapes and wine as free, volatile and odorous molecules, as well as in flavourless, nonvolatile glycosidic complexes. These complexes most often occur as 6-0-a-L-arabinofuranosyl-p-D-glucopyranosides (vicianosides), 6-0-P-D-xylopyranosyl- P-D-gluco-pyranosides (primverosides), 6-0-P-D-glucopyranosyl-p-D-glucopyranosides (gentio-biosides ), 6-0-a-L -rhamnopyra nosyl-p-D-g lucopyra nos ides (rutinos ides), or 6-0-p-D-apiofuranosyl-p-D-glucopyranosides of mainly linalool, geraniol, nerol, a-terpineol and hotrienol. These precursors are, however, hydrolyzed only to a limited extent by endogenous glycosidases during the fermentation process, as they exhibit very low activity in wine conditions. The monoterpenols can be released from their sugar moieties by one of two methods: either an acid or an enzymatic hydrolysis. The enzymatic hydrolysis mechanism is fully understood, and the process functions in two successive steps: firstly, depending on the precursor, the glycosidic linkage is cleaved by an a-L-arabinofuranosidase, an a-L-rhamnosidase, a p-D-xylosidase, or a p-D-apiosidase. The second step involves the liberation of the monoterpene alcohol by a p-glucosidase. This enzymatic hydrolysis does not influence the intrinsic aromatic characteristics of the wine, as opposed to acid hydrolysis. As the endogenous grape glycosides of Vitis vinifera and the yeast Saccharomyces cerevisiae show very low activity towards these aromatic precursors during the handling of the juice and winemaking processes, the focus has increasingly fallen on introducing exogenous p-glucosidases to wines and juices. Genes encoding p-glucosidases and a-L-arabinofuranosidases have been cloned from various organisms, including bacteria, fungi and yeasts. However, the activities and properties of these enzymes are not always suitable for exploitation under winemaking conditions, where a low pH, low temperatures, and high ethanol and glucose concentrations prevail. A genetically engineered wine yeast strain of S. cerevisiae that expresses glycosidases that are active in these conditions would be useful in improving the flavour and aroma of wines, thereby adding to the complexity and value of the wine. Two p-glucosidase genes, BGL 1 and BGL2 from Saccharomycopsis fibufigera, were subcloned into two Escherichia coli-yeast shuttle vectors. A dominant selectable marker gene (SMR1) was also inserted onto these plasmids. These plasmids were designated pBGL 1 (containing the BGL 1 gene) and pBGL2 (containing the BGL2 gene) respectively. Introduction of the two plasmids into two strains of S. cerevisiae then followed. A laboratory strain, L1278, was transformed to confirm the effective secretion of the expressed protein. An industrial yeast strain, VIN13, was subsequently transformed by making use of the selectable marker (resistance against sulfometuron). Enzyme assays with the synthetic substrate p-nitrophenol-j3-D-glucopyranoside (pNPG) were performed to determine the activity of the j3-glucosidases over a period of days, as well as at certain temperatures and pH values. The stability of the enzymes was also investigated. These recombinant yeasts were able to degrade the pNPG efficiently. They showed promising results concerning pH optima, with a substantial amount of activity found at the pH levels as found in the wine environment. There was also a slight increase in specific activity at lower temperatures. The recombinant yeast strains were also tested in smallscale fermentations. Three wines were made, of which two were from white cultivars (Chenin blanc and GewOrtztraminer) and one from red (Pinotage). Results obtained from micro-extraction from the finished wines showed that the terpenol content did increase, although this was not the only wine component influenced. Other flavour compounds also showed increases, especially the esters. This also played a role in the flavour increase in the wine. Future work would include optimizing the available results. This would entail the addition of another glycosidic enzyme, such as a-L-arabinofuranosidase, to the genome of the wine yeast to aid the further breakdown of glycosidic bonds. The cloning or engineering of a j3-glucosidase enzyme that is more active at low temperatures would also yield better results and release even more of the aroma of the wine. / AFRIKAANSE OPSOMMING: Monoterpeenalkohole (monoterpenole) speel 'n belangrike rol in die geur en aroma van druiwe en wyn. Dit is veral van toepassing op wyne van Muskaat-varieteite, maar hierdie geurkomponente is ook teenwoordig in ander nie-Muskaat druifsoorte, waar dit bydra tot die varieteitsqeur en aroma. Hierdie monoterpenole kom voor in druiwe as vry, vlugtige en aromatiese molekules, of as geurlose, nie-vlugtige glikosidies-gebonde komplekse. Hierdie komplekse is meestal in die vorm van 6-0-a-L-arabinofuranosiel-~-D-glukopiranosiede, 6- O-~-D-xilopiranosiel-~-D-glukopiranosiede (primverosiede), 6-0-~-D-glukopiranosiel-~-Dglukopiranosiede (gentiobiosiede), 6-0-a-L-ramno-pyranosiel-~-D-glukopiranosiede (rutinosiede), of 6-0-~-D-apiofuranosiel-~-D-glukopirano-siede van hoofsaaklik linalool, geraniol, nerol, a-terpineol en hotrienol. Hierdie geurvoorlopers word egter slegs tot In beperkte mate tydens die proses van fermentasie deur die endogene glikosidase ensieme gehidroliseer, aangesien hulle baie min aktiwiteit toon onder wynbereidingstoestande. Die monoterpenole kan op een van twee wyses van hul suikermolekules vrygestel word: 'n suurhidrolise, of ensiematiese hidrolise. Die ensiematiese hidroliseproses word baie goed begryp en behels twee opeenvolgende stappe: eerstens, afhangende van die aard van die voorloper, word die glikosidiese verbinding deur In a-L-arabinofuranosidase, In a-L-ramnosidase, In ~-D-xilosidase, of 'n ~-D-apiosidase gebreek. In die tweede stap word die monoterpeenalkohol deur In ~-glukosidase vrygestel. Hierdie ensiematiese afbraakproses verander nie die intrinsieke aromatiese kenmerke van die wyn, soos wat met suurhidrolise die geval is nie. Omdat die endogene glikosidases van Vitis vinifera en die van die gis Saccharomyces cerevisiae baie lae aktiwiteit ten opsigte van die aromatiese voorlopers gedurende die hantering van die druiwesap en wynmaakprosesse toon, val die fokus al hoe meer op die inkorporering van eksogene ~-glukosidases in wyn en sappe. Gene wat vir ~- glukosidases en a-L-arabinofuranosidases kodeer, is al vanuit verskeie organismes gekloneer, insluitende bakteriee, fungi en giste. Die aktiwiteite en kenmerke van hierdie ensieme is egter nie altyd wenslik vir hul gebruik in wyn nie, aangesien dit In omgewing is met 'n lae pH, lae temperatuur, en hoe etanolvlakke en glukose-konsentrasies. In geneties veranderde wyngis van S. cerevisiae wat in staat is om glikosidases uit te druk wat onder hierdie kondisies aktief is, sal baie handig te pas kom in die verbetering van die geur en aroma van wyne, om daardeur die kompleksiteit en die waarde van die wyn te verhoog. Twee ~-glukosidasegene, BGL 1 en BGL2 vanaf die gis Saccharomycopsis fibuligera , is in twee afsonderlike Esccherichia coli-gis-pendelplasmiede gesubkloneer. In Dominante selekteerbare merkergeen (SMR1) is ook in hierdie plasmiede gekloneer. Hierdie plasmiede word onderskeidelik pBGL 1 (met die BGL 1-geen) en pBGL2 (bevattende die BGL2-geen) genoem. Hierdie twee plasmiede is hierna apart na twee rasse van S. cerevisiae getransformeer. Eerstens is 'n laboratoriumras, L1278, getransformeer om te bevestig dat effektiewe sekresie en uitdrukking van die proteTen plaasvind. Hierna is 'n industriele gisras, VIN13, getransformeer deur gebruik te maak van die selektiewe merker (bestandheid teen sulfometuron). Ensiem-bepalings met behulp van die sintetiese substraat p-nitrofeniel-p-O-glukopiranosied (pNPG) is gedoen om die aktiwiteit van die p-glukosidqses oor 'n aantal dae te bepaal, asook om die aktiwiteit by sekere temperature en pH-vlakke te meet. Die stabiliteit van die ensieme is ook bepaal. Hierdie rekombinante giste was in staat om pNPG effektief af te breek. Hulle het belowende resultate betreffende die pH-optima getoon, met 'n aansienlike hoeveelheid aktiwiteit by die pH-vlakke soos dit in die wynomgewing voorkom. Daar was ook 'n effense verhoging in die ensieme se aktiwiteite by laer temperature. Die rekombinante gisrasse is ook in kleinskaalse wynfermentasies gebruik. Drie verskillende wyne is gemaak, waarvan twee wit kultivars was (Chenin blanc en GewOrtztraminer) en een 'n rooi kultivar (Pinotage). Resultate wat deur die mikro-ekstraksie van die voltooide wyne verkry is, het getoon dat die terpenolinhoud wei verhoog het, alhoewel dit nie die enigste wynkomponente was wat beinvloed is nie. Ander geurkomponente het ook 'n verhoging in konsentrasie getoon, veral die esters. Hierdie verbindings het ook 'n rol in die verhoging van geur in die wyne gespeel. Toekomstige werk sal die beskikbare resultate verder optimaliseer. Dit sal insluit die byvoeging van nog 'n glikosidiese ensiem, soos a.-L-arabinofuranosidase, tot die genoom van die wyngis, om verdere afbraak van glikosidiese verbindings teweeg te bring. Die klonering of verandering van 'n p-glukosidase-ensiem met verhoogde aktiwiteit by laer temperature sal ook beter resultate toon en meer geur in die wyn kan vrystel.

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The winemaking process involves a complex microbial flora where the interaction of yeasts, lactic acid bacteria and acetic acid bacteria play an important role in the quality and wholesomeness of the final product. Yeasts are primarily responsible for alcoholic fermentation. Malolactic fermentation follows alcoholic fermentation and is conducted by lactic acid bacteria. These bacteria are important in winemaking and can have a positive or negative effect on the wine quality. Biogenic amines are one of the compounds produced by lactic acid bacteria, which affect the hygienic quality and wholesomeness of the wine negatively and directly pose a health risk to the consumer. The demand of consumers for higher quality and healthier foods has led to renewed interest in studies on biogenic amines. Biogenic amines occur in a wide variety of food products, such as cheese, dried sausage, sauerkraut, fishery products, chocolates, wine and beer. This thesis focussed on the presence of biogenic amines in wine. The first objective of the study was to determine the ability of lactic acid bacteria isolated from South African wine to produce biogenic amines, using a decarboxylase screening plate method. The potential to produce the biogenic amines histamine, tyramine, putrescine and cadaverine was investigated. The results obtained showed that Lactobacillus species (Lactobacillus brevis and Lactobacillus hilgardil) might be the lactic acid bacteria responsible for tyramine and putrescine production and that it can contribute significantly to the overall biogenic amine content in wines. The results also suggest that amine production is strain dependent and not species specific. None of the lactic acid bacteria tested had the ability to produce histamine or cadaverine. It is important to remember that the ability of the lactic acid bacteria to produce biogenic amines has only been investigated in synthetic media and that it does not necessarily imply similar behaviour in wine. Wine represents a complex environment with a wide number of factors influencing microbial growth and decarboxylase activity and, thus, further investigation is necessary to determine if these amine-producing bacteria behave similarly in wine conditions. In addition, the polymerase chain reaction (PCR) amplification method was used for the identification of the tyrosine decarboxylase (TOe) gene in some of the tyramine-producing lactic acid bacteria. This was followed by the sequencing of the amplified products, which are partial TOe gene sequences, of two L. brevis strains and of a L. hilgardii strain. Only one tdc gene sequence has been described for bacteria (Enterococcus faecalis), while a partial TOC gene sequence from L. brevis lOEB 9809 was described. An amino acid sequence alignment of the three TOe gene fragments, obtained in this study, with the known TOe gene fragment of L. brevis lOEB 9809 and the tdc gene of E. faecalis showed a high degree of relatedness and conserved regions. To meet consumer demands, procedures are necessary to prevent the formation of amines in food products. One way of preventing the formation of biogenic amines is to relate amine production with certain lactic acid bacteria species involved in the winemaking process. Another possible way would be to develop a rapid detection method for bacteria carrying amino acid decarboxylase genes. The results of this study provide knowledge about which lactic acid bacteria in the winemaking process could contribute to the production of biogenic amines and the sequencing of additional partial TOe genes could possibly assist in the development of a rapid detection method for tyramine-producing lactic acid bacteria in food products. / AFRIKAANSE OPSOMMING: Die wynmaakproses behels 'n komplekse mikrobiese flora waar die interaksie van giste, melksuurbakterieë en asynsuurbakterieë 'n belangrike rol speel in die kwaliteit en heilsaamheid van die finale produk. Giste is primêr verantwoordelik vir alkoholiese fermentasie. Appelmelksuurgisting volg op alkoholiese fermentasie en word deur melksuurbakterieë uitgevoer. Hierdie bakterieë is belangrik in die maak van wyn en kan 'n positiewe of negatiewe uitwerking op die kwaliteit van wyn hê. Biogeniese amiene is een van die komponente wat deur melksuurbakterieë geproduseer kan word en wat die higiëniese kwaliteit en heilsaamheid van die wyn benadeel. Dit hou ook 'n gesondheidsrisiko vir die verbruiker in. Die vereiste van verbruikers vir hoër kwaliteit en gesonder voedselprodukte het nuwe belangstelling in studies op biogeniese amiene ontlok. Biogeniese amiene kom in 'n wye verskeidenheid voedselprodukte voor, soos kaas, droëwors, suurkool, vis, sjokolade, wyn en bier. Hierdie tesis fokus op die teenwoordigheid van biogeniese amiene in wyn. Die eerste doelwit van die studie was om melksuurbakterieë, wat uit Suid- Afrikaanse wyn geïsoleer is, se vermoë te bepaal om biogeniese amiene op dekarboksilase-agarplate te produseer. Die potensiaal om die biogeniese amiene histamien, tiramien, putresien en kadawerien te produseer, is bestudeer. Die resultate wat verkry is, toon dat Lactobacillus-spesies (Lactobacillus brevis en Lactobacillus hilgardit) vir tiramien- en putresienproduksie verantwoordelik is en dat hulle 'n belangrike bydrae kan lewer tot die totale biogeniese amienkonsentrasie in wyn. Die resultate dui ook daarop dat die produksie van amiene afhanklik is van die ras, en nié 'n spesifieke spesie nie. Geen melksuurbakterieë wat getoets is, het die vermoë getoon om histamien of kadawerien te produseer nie. Dit is belangrik om in ag te neem dat die vermoë van die melksuurbakterieë om amiene te produseer slegs in sintetiese media bestudeer is en dat dit nie noodwendig dieselfde gedrag in wyn sal toon nie. Wyn is 'n komplekse omgewing met 'n wye verskeidenheid faktore wat die mikrobiese groei en dekarboksilase-aktiwiteit kan beïnvloed, daarom is verdere studie nodig om vas te stelof hierdie amien-produserende bakterieë dieselfde gedrag in wyn sal toon. Die polimerase-kettingreaksie (PKR) amplifikasie-metode is vir die identifikasie van die tirosiendekarboksilase-geen (TDK) in sommige van die tiramienproduserende melksuurbakterieë gebruik. Dit is gevolg deur die volgordebepaling van die geamplifiseerde produkte, wat gedeeltelike TDK-geenvolgordes is, van twee L. brevis- en van een L. hilgardii-ras. Slegs een tdk-geenvolgorde is al voorheen vir bakterieë beskryf, nl. Enterococcus faecalis, asook 'n gedeeltelike TDK-geenvolgorde vir L. brevis lOEB 9809. 'n Vergelyking van die aminosuurvolgordes van die drie TDK-geenfragmente wat in die studie verkry is, het 'n hoë graad van ooreenkoms en gekonserveerde areas met die bekende TDK-geenfragment van L. brevis lOEB 9809 en die tdk-geen van E. faecalis getoon. Om verbruikers se behoeftes te bevredig, is dit noodsaaklik dat die vorming van amiene in voedselprodukte voorkom word. Een manier van voorkoming is om amienproduksie aan sekere melksuurbakterieë wat in die wynmaakproses betrokke is, te koppel. 'n Ander manier sal wees om 'n vinnige metode te ontwikkel vir die opsporing van bakterieë wat aminosuurdekarboksilase-gene dra. Die resultate van die studie verskaf kennis van watter melksuurbakterieë in die wynmaakproses tot die produksie van biogeniese amiene kan bydra. Die volgordebepaling van addisionele gedeeltelike TDK-gene kan moontlik tot die ontwikkeling van 'n vinnige opsporingsmetode van tiramien-produserende melksuurbakterieë in voedselprodukte bydra.