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Sensory and chemical evaluation of riesling, chardonnay and pinot noir fermented by different strains of Saccharomyces cerevisiaeDumont, Ann 23 November 1994 (has links)
Fermentation of the grape must into wine is one of the most important steps
in winemaking. Selected yeast strains of Saccharomyces cerevisiae have
been used for many years to ensure complete and even fermentations. The
formation of volatile compounds also occurs during fermentation and will
influence the sensory perception of the wine. The main objective of the
research was to study the sensory and chemical composition of 1992 Oregon
Riesling, Chardonnay and Pinot Noir wines fermented with different
commercial S.cerevisiae strains.
In the first study, Free-Choice Profiling was used to study the sensory
profiles of all three varieties after 7 and 20 months of aging. This method was
used in order to utilize a panel of expert winemakers for the tastings. The
sensory data analyzed through Generalized Procrustes Analysis showed that
some strains were similar while others were different in terms of aroma and
flavor at 7 months of age. After 20 months of aging, differences and
similarities were still present although the sensory profiles were different from the young wines. This last finding showed that differences are still present
after a period of aging.
In the second study, the chemical composition of all three varieties and the
volatile composition of selected wines of Riesling and Chardonnay were
studied. In both white varieties, statistical differences in titratable acidity,
residual sugar, volatile acidity and malate content resulted from fermentation
with different yeast strains. The volatile composition was qualitatively similar,
but some quantitative differences, as relative concentration, were found.
Whether or not those differences had a sensory impact was not investigated.
Results of the present study showed the need for further studies in order to
understand the role of yeast in flavor development. Relationships between
sensory profiles and volatile composition could help winemakers to
understand the influence of a selected strain on a particular variety and to
select yeast strains to optimize wine quality. / Graduation date: 1995
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Consumer acceptance of a selection of South African red wines : intrinsic, extrinsic and socio-demographic influencesBasson, Shantelle 03 1900 (has links)
Thesis (MSc Food Sc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: In this study an industry-selected and diverse range of South African red wines were analysed for sensory and chemical attributes, as well as degree of liking using a target group of black South African consumers. Segments of consumers that differed in degree of liking were then tested for their response to intrinsic (sensory) and extrinsic (non-sensory) cues.
The selection of wines included eighteen dry and natural sweet red wines, representing low-end inexpensive wines together with high-end, top quality wines. Sensory profiles for all samples were established using Quantitative descriptive analysis (QDA). The results revealed that cultivar specific dry red wines associated with a wide range of sensory descriptors such as woody, vegetative and fruity, while the sweet red wines associated with the fruity and sweet-associated attributes.
Chemically there was a significant variation between wines regarding the alcohol and sugar content. Gas chromatography with flame ionisation detection (GC-FID) indicated the major volatile constituents present in the wine, i.e. esters, alcohols and fatty acids.
When investigating the association between the chemical and sensory data, it was revealed that the red blends were driven by the presence of alcohols and esters, and sensory descriptors such as high roast oak, coffee and mixed spice, whereas the red cultivar wines were mostly driven by fatty acids and esters and the sensory descriptors, green bean and asparagus. The sweet red blends were closely associated with acids and the sensory descriptors sweet-associated and floral.
Degree of liking of a subset of 18 wines was investigated based on the preferences of black consumers from the Western Cape area, South Africa. These consumers predominantly preferred the sweet red wines with high sugar content, in a blind tasting session. Purchase intent was also evaluated by viewing actual photographs of packaging formats of the respective wines and the results indicated that the consumers preferred the well-known cultivar wines with a perception of value and style.
Cluster analysis was furthermore performed to ascertain whether these consumers differed in their degree of liking of the intrinsic character of the respective wines. Four different clusters of consumers were identified: 1) Consumers preferring both dry and sweet red wines equally, 2) Consumers who strongly favoured sweet red wines and moderately liked dry red wines, 3) Consumers who strongly favoured sweet red wines with little preference for dry red wines; and 4) Consumers preferring dry red wines. Consumers were also probed on their general opinions or perceptions on the extrinsic character of the wines, and thus factors that influence the purchasing process. It was found that black consumers who don‟t consume wine often, preferred wines that they are familiar with, while consumers that drink wine more frequently enjoy to broaden their horizons by experimenting with more expensive wine brands.
Extrinsic or non-sensory cues such as alcohol content, label, vintage, price and cultivar were found to be the most important considered factors when purchasing red wines, while awards and type of closure were regarded as the least important. It was also found that the discerning consumers, who purchase high-end wines, took more of the latter aspects into consideration, whereas consumers who purchase low-end wines considered a limited number of the non-sensory cues. / AFRIKAANSE OPSOMMING: In hierdie studie is 'n diverse reeks industrie-geselekteerde, Suid-Afrikaanse rooiwyne geanaliseer vir hul sensoriese en chemiese eienskappe. Verbruikersvoorkeur van die wyne is getoets, asook tot watter mate verbruikersvoorkeure beïnvloed word deur intrinsieke (sensoriese) en ekstrinsieke (nie-sensoriese) faktore.
Die reeks van agtien wyne het bestaan uit droë en soet rooi wyne, wat op hul beurt verder verdeel kan word in goedkoper, kwaliteit wyne en duurder, ultra-premium wyne. Die sensoriese profiel van al die wyne is bepaal deur beskrywende sensoriese analise. Resultate het getoon dat die kultivar-spesifieke droë rooiwyne geassosieer word met 'n wye reeks sensoriese eienskappe soos houtagtig, kruidagtig en vrugtig, terwyl die soet rooiwyne beskryf is as vrugtige en soet-geassosieerd.
In terme van die chemiese analises was daar betekenisvolle verskille betreffende die alkohol- en suikerinhoud van die wyne. Gas chromatografie gekoppel met vlam-ioniserende deteksie (GC-FID) het die mees vlugtige verbindings teenwoordig in die wyn aangedui, naamlik esters, alkohole en vetsure.
Met die korrelasie van die chemiese en sensoriese data is gevind dat die droë versnitwyne gedryf word deur die teenwoordigheid van alkohole en esters, asook sensoriese eienskappe soos gehout, koffie, en gemengde spesery, terwyl die kultivar-spesieke wyne weer meestal gedryf word deur vetsure en esters en sensoriese eienskappe soos groenboontjie en aspersie. Die soet rooiwyne het chemies geassosieer met sure en sensoriese terme soos soet-geassosieerd en blomagtig.
Die aanvaarbaarheid van 'n kleiner groepering wyne is bepaal deur gebruik te maak van swart verbruikers in die Wes-Kaap area, Suid-Afrika. Die verbruikers het in 'n blinde proesessie onderskeie wyne se wynverpakking besigtig en aangedui of hulle die wyne sou koop. Hierdie resultate het getoon dat die verbruikers bekende kultivarwyne verkies wat 'n persepsie van waarde en styl geïllustreer het.
Segmentasie tegnieke is op die data uitgevoer ten einde te bepaal of verbruikers in groepe verdeel kan word, wat betref hul voorkeur van die sensoriese of intrinsieke eienskappe van die wyne. Vier verskillende groepe is geïdentifiseer, nl. verbruikers wat 1) droë en soet rooiwyne ewe veel verkies; 2) soet rooiwyne en tot 'n mate ook droë rooiwyne verkies; 3) soet rooiwyne en tot 'n mindere mate droë rooiwyne verkies; en laastens 4) slegs droë rooiwyne verkies. Verbruikers se algemene opinies en persepsies betreffende die ekstrinsieke eienskappe van die wyne is ook ondersoek, met ander woorde faktore wat die aankoop van wyne beïnvloed. Daar is gevind dat swart verbruikers wat nie gereeld wyn drink, bekende handelsmerke verkies, terwyl verbruikers wat gereeld wyn drink, daarvan hou om hul horisonne te verbreed en te eksperimenteer met 'n verskeidenheid handelsmerke.
Ekstrinsieke of nie-sensoriese aspekte soos, alkohol-inhoud, etiket, oesjaar, prys en kultivar is die belangrikste faktore wat in ag geneem word wanneer rooiwyne gekoop word, terwyl wyntoekennings en die feit dat die wyn met kurke gebotteleer word, nie as belangrik beskou word nie. Daar is ook gevind dat die meer ingeligte verbruiker, wat hoë kwaliteit wyne koop, meer van die bogenoemde aspekte in ag neem tydens die aankoopproses, terwyl die verbruiker wat meer geneig is om goedkoper wyne te koop, slegs 'n paar ekstrinsieke faktore in ag neem.
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Application of modern chromatographic technologies for the analysis of volatile compounds in South African winesWeldegergis, Berhane Tekle 12 1900 (has links)
Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT:
The present study was initiated by the wine industry of South Africa to overcome the
lack of available information on the flavor and aroma of South African wines. The
aim was to develop new analytical methods and improve existing ones for the analysis
of volatile compounds in the South African wines. Initially a new analytical method
based on stir bar sorptive extraction (SBSE) in the headspace mode for the analysis of
37 pre-selected volatile compounds was developed and validated. Consequently, the
method was improved by making important modifications and increasing the number
of compounds analyzed to 39. This method was successfully applied to a large
number of Pinotage wines of vintages 2005 and 2006. The quantitative data of these
wines were subjected to chemometric analysis in order to investigate possible co-
/variances. A clear distinction was observed between the two vintages, where the
2005 wines were more characterized by wood-related compounds and the 2006 wines
by the fermentation compounds. The developed method was further applied to other
cultivars of vintage 2005, including two white (Sauvignon Blanc and Chardonnay)
and three red (Shiraz, Cabernet Sauvignon and Merlot) cultivars. In a similar fashion,
the quantitative data of the six cultivars of vintage of 2005 were analysed by
chemometric methods. Significant differences were observed between the two white
cultivars and among the four red cultivars. It was shown that among these cultivars,
the major role-players were the wood and fermentation related volatiles. A striking
observation was the confirmation of the unique character of the Pinotage wines
compared to the other red cultivars, mainly influenced by the high level of isoamyl
acetate and low level of isoamyl alcohol, the former being categorized as a varietal
compound for Pinotage expressed by a fruity (banana) odor.
In addition, advanced chromatographic technology in the form of comprehensive twodimensional
gas chromatography (GC × GC) coupled to time-of-flight mass
spectrometry (TOFMS) was investigated for the detailed analysis of volatile
compounds in young South African wines. This work focused primarily on Pinotage
wines. In the first instance, solid phase micro extraction (SPME) in the headspace
mode in combination with GC × GC-TOFMS was used. Due to the high resolution
and large peak capacity of GC × GC, more than 200 compounds previously reported
as wine components were identified. These compounds were dominated by the highly volatile and less polar compounds, mainly due to the characteristics of SPME. In an
attempt to further extend these results, another selective extraction method, solid
phase extraction (SPE) was used in combination with GC × GC-TOFMS analysis.
Using this technique, more than 275 compounds, most of them unidentified using the
previous method, were detected. These groups of compounds include volatile phenols,
lactones as well as mostly aromatic esters and norisoprenoids, which can potentially
influence the aroma and flavor of wine. The techniques developed as part of this study
have extended our knowledge of the volatile composition of South African wines. / AFRIKAANSE OPSOMMING:
Hierdie studie is geïnisieer deur die wyn industrie van Suid-Afrika om die tekort aan
beskikbare inligting aangaande wyn aroma van Suid-Afrikaanse wyne te oorkom. Die
doel was om nuwe analitiese metodes te ontwikkel en die huidige metodes te verbeter
vir die analise van vlugtige verbindings in Suid-Afrikaanse wyne. Oorspronklik is ʼn
nuwe analitiese metode ontwikkel en gevalideer gebaseer is op ‘stir bar sorptive
extraction’ (SBSE) in die gas fase vir die analise van 37 vooraf geselekteerde vlugtige
verbindings. Die metode is verbeter deur belangrike modifikasies aan te bring en die
hoeveelheid verbindings wat analiseer word te vermeerder na 39. Hierdie metode is
suksesvol aangewend op ʼn groot hoeveelheid Pinotage wyne van oesjare 2005 en
2006. Die kwantitatiewe data van hierdie wyne is onderwerp aan verskillende
chemometriese analises om moontlike ko-/variasies te ondersoek. ʼn Duidelike
onderskeid is opgemerk tussen die twee oesjare, waar die 2005 wyne gekarakteriseer
is deur hout-verwante verbindings en die 2006 wyne weer meer deur fermentasie
verbindings. Die verbeterde metode is verder aangewend vir analiese van ander
kultivars van oesjare 2005, wat twee wit (Sauvignon Blanc en Chardonnay) en drie
rooies (Shiraz, Cabernet Sauvignon en Merlot) ingesluit het. Die kwantitatiewe data
van die ses kultivars van oesjaar 2005 is op ʼn soortgelyke wyse geanaliseer deur
verskillende chemometriese metodes te gebruik. Beduidende verskille is opgemerk
tussen die twee wit kultivars en tussen die vier rooi kultivars. Die hoof rolspelers
tussen die ses kultivars was weereens die verbindings wat ʼn hout en fermentasie aard
het. Die unieke karakter van die Pinotage wyne in vergelyking met die ander rooi
kultivars was opvallend. Hierdie wyn word gekarakteriseer deur hoë vlakke van
isoamiel asetaat en lae vlakke van isoamiel alkohol, waar eersgenoemde gekatogiseer
word as ʼn verbinding wat ʼn vrugte (piesang) geur in Pinotage uitdruk.
Verder is gevorderde chromatografiese tegnologie in die vorm van ‘comprehensive
two-dimentional gas chromatography’ (GC x GC) gekoppel met ‘time-of-flight mass
spectroscopy’ (TOFMS) ondersoek vir die analiese van vlugtige verbindings in jong
Suid-Afrikaanse wyne. Hierdie werk het hoofsaaklik op Pinotage wyne gefokus.
Eerstens is ‘solid phase micro extraction’ (SPME) in die gas fase gekombineer met
GC x GC-TOFMS. As gevolg van die hoë resolusie en groot piek kapasiteit van GC x
GC is meer as 200 verbindings wat voorheen gerapporteer is as wyn komponente geïdentifiseer. Hierdie verbindings is gedomineer deur hoë vlugtige polêre
verbindings, hoofsaaklik as gevolg van die karaktersitieke van SPME..In ʼn poging om
die metode verder te verbeter is ʼn selektiewe ekstraksie metode naamlik ‘solid phase
extraction’ (SPE) in kombinasie met GC x GC-TOFMS gebruik. Met hierdie tegniek
is meer as 275 verbindings geïdentifiseer, waarvan die meeste nie met die vorige
metode waargeneem is nie. Hierdie verbindings sluit vlugtige fenole, laktone en
meestal aromatiese esters en norisoprenoïdes in, wat moontlik die reuk en smaak van
wyn kan beïnvloed. Die metodes ontwikkel gedurende die studie het nuwe informasie
verskaf aangaande die vlugtige komponente teenwoordig in Suid Afrikaanse wyne.
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Stir bar sorptive extraction for the analysis of beverages and foodstuffsTredoux, A. G. J. 03 1900 (has links)
Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2008. / The main goal of this study was the development of new technologies based on modern
analytical techniques for analysis of volatiles in wines. Due to the exponential growth of
the wine industry and consumer demands for an enjoyable, safe-to-consume, and high
quality product, the need for arose for methodologies aiding the understanding of wine
better arose. Chemical analysis is a valuable way of studying the composition of wine in
depth. Very sophisticated instrumentation is available nowadays but almost always the
sample needs to be cleaned up or concentrated before such analysis. This study
investigates the use of stir bar sorptive extraction (SBSE) as such a technique. It is shown
that SBSE combined with gas chromatography-mass spectrometry (GC-MS) is extremely
suited for a wide number of analyses and during the course of the study the technique was
applied for troublesome analytical challenges in various beverages and foodstuffs. The
study focuses on the development of a screening technique for volatiles in wine using
SBSE and the application of the data to various chemometrical techniques for
classification purposes. A second part of the study shows the applicability of SBSE for
extraction of pesticides, contaminants and preservatives from wine, water, lemon
flavoured beverages and yoghurt. The method is also elaborated upon by development of
faster analysis methods for wine and beer and the investigation of using SBSE for
headspace sampling of wine. In all the applications, SBSE technology was shown to be
sensitive, repeatable, robust and very simple to use.
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Investigation into the mechanism of action and biological role of Saccharomyces cerevisiae mannoproteins which reduce visible haziness in white wineBrown, Shauna L January 2003 (has links)
Heat induced protein haze is a common problem in white wine. Grape derived pathogenesis related proteins slowly denature and aggregate during wine storage and this gives rise to light dispersing haze. Protein haze formation is currently prevented by removing proteins using bentonite, an aluminium silicate clay, but this method has drawbacks. A potential alternative or complementary method is the use of haze protective factors ( HPF ), specific mannoproteins from Saccharomyces cerevisiae that visually reduce protein haze. Hpf1p was originally isolated from Muscat Gordo Blanco wine and Hpf2p from a synthetic grape juice ferment. Based on partial amino acid sequences, putative structural genes, HPF1 and HPF2, for these proteins were identified. HPF1 has a homologue, HPF1 ', ( 71 % similarity ) in S. cerevisiae. Sequence analysis suggests that Hpf1p, Hpf1 ' p and Hpf2p are localised to the cell wall or plasma membrane. This study aimed to determine the biological function of the HPF genes in S. cerevisiae. HPF overexpression and deletion strains were constructed and analysed for cell wall related phenotypes. Under a number of conditions, including cold temperature and ethanol stress, the hpf1 Δ hpf1 ' Δ strain was more tolerant than the wild type strain. However, mating efficiency of the hpf1 Δ hpf1 ' Δ strain was significantly less than the wild type strain and this was found to be correlated with the persistence of a septum between the mating partners. The decreased mating efficiency was also mating type specific, only occurring in MAT α cells. This study also aimed to establish conclusively that the HPF genes do indeed encode proteins with haze protective properties. Haze protective activity of the material from ferment supernatants was assessed. Material from the HPF deletion strains exhibited significantly less haze protective activity than the wild type. Moreover, material derived from HPF1 and HPF1 ' overexpressors was more active than material from the wild type. A 6xHis - tagged Hpf2p was expressed and purified using immobilised metal affinity chromatography. This Hpf2p had significant haze protective activity. Modification of N - glycans of 6xHis - Hpf2p by Endoglycosidase H decreased its haze protective activity.visually reduce protein haze. Hpf1p was originally isolated from Muscat Gordo Blanco wine and Hpf2p from a synthetic grape juice ferment. Based on partial amino acid sequences, putative structural genes, HPF1 and HPF2, for these proteins were identified. HPF1 has a homologue, HPF1 ', ( 71 % similarity ) in S. cerevisiae. Sequence analysis suggests that Hpf1p, Hpf1 ' p and Hpf2p are localised to the cell wall or plasma membrane. This study aimed to determine the biological function of the HPF genes in S. cerevisiae. HPF overexpression and deletion strains were constructed and analysed for cell wall related phenotypes. Under a number of conditions, including cold temperature and ethanol stress, the hpf1 Δ hpf1 ' Δ strain was more tolerant than the wild type strain. However, mating efficiency of the hpf1 Δ hpf1 ' Δ strain was significantly less than the wild type strain and this was found to be correlated with the persistence of a septum between the mating partners. The decreased mating efficiency was also mating type specific, only occurring in MAT α cells. This study also aimed to establish conclusively that the HPF genes do indeed encode proteins with haze protective properties. Haze protective activity of the material from ferment supernatants was assessed. Material from the HPF deletion strains exhibited significantly less haze protective activity than the wild type. Moreover, material derived from HPF1 and HPF1 ' overexpressors was more active than material from the wild type. A 6xHis - tagged Hpf2p was expressed and purified using immobilised metal affinity chromatography. This Hpf2p had significant haze protective activity. Modification of N - glycans of 6xHis - Hpf2p by Endoglycosidase H decreased its haze protective activity. / Thesis (Ph.D.)--School of Agriculture and Wine, 2003.
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The Terroir of Pinot Noir Wine in the Willamette Valley, Oregon : A Broad Analysis of Vineyard Soils, Grape Juice and Wine ChemistryBarnard, Kathryn Nora 02 June 2016 (has links)
Terroir is determined by a combination of factors in the vineyard including the grape varietal, geology and soil, soil hydrology, physiography, and climate. Although most studies have examined regional differences in wine flavors and associated provenance of wine based on chemistry, few have examined the chemistry of the soil and the ability to trace that chemistry to grape juice and, finally, to the wine. This dissertation examines what soil physical and chemical differences specific to this region might influence grape juice chemistry and wine chemistry.
Wine-grapes in the Willamette Valley, Oregon, are grown on three major soil parent materials: volcanic, marine sediments, and loess/volcanic. Winemakers have observed differences in the flavor of Pinot Noir wine made from grapes grown on these different parent materials. This dissertation examines differences in the soil properties and elemental chemistry of the soil parent materials at various vineyards to document their effect on wine chemistry as a step towards understanding differences in flavor. All aspects of the terroir are controlled by carefully selecting vineyards with similar exposure and elevation, the same grape varietal and wine making techniques, and only the soils vary. The hypothesis is that the chemistry of the grape juice and wine reflect the soil in which the grapes were grown and that the three parent materials have soils that can be distinguished by their physical and chemical characteristics.
Soil pits were excavated in 20 vineyards, soil properties were described in the field, and soil samples were later analyzed in the laboratory particle size, organic matter, color, pH, cation exchange capacity (ammonium acetate method), clay mineralogy (x-ray diffraction), and elemental chemistry (ICP-MS/AES). X-ray fluorescence was used to examine the pisolites. ICP-MS/AES was used for elemental analysis of grape juice and wines produced from these vineyards. Principal component analysis was used to compare soil physical and chemical characteristics, grape juice and wine chemistry.
The physical characteristics of soils from all the three parent materials indicate: they are old (>50,000 years) based on their high clay content, low cation exchange capacity, red colors, and high Fe and Al content. These features indicate enough time has passed to reduce organic matter and other cations at depth, leave behind insoluble Fe and Al, and develop pedogenic clays. In my study region, volcanic and marine sediment soils are more developed with slightly lower acidity than the loess/volcanic soils. A new finding for this region is the presence of pisolites (Fe/Mg concretions) in the volcanic and the loess/volcanic soils, but absent in the marine sediment soils. Winemakers hypothesized that pisolites were present only in loess soils and influenced wine flavor in some way.
Volcanic soils have the highest P, S, Fe, Co, Mn, and V concentrations and the lowest As and Sr values. Marine sediment soils have higher Cl and Sr and lower P, Co, Mn, Ba, and V concentrations than volcanic soils. Loess soils have the highest values of K and Mg and are similar to volcanic soils with higher P and V values and similar to marine sediment soils with higher Sr values. The main elements found to be significant in determining one parent material from another are V and Mn (volcanic soils), Mg and K (loess soils), and Sr (marine sediment or loess soils). Sr is slightly higher in grape juice and wine from vines grown on marine sediment parent material compared to volcanic and loess parent material, whereas Mn is higher in the juice and wine from grapes grown in volcanic parent material. P, S, Fe, Co, V, Cl, Ba, Mg, and K did not maintain their relative concentration levels from soil to grape juice to wine. The principal component analysis shows that soil and wine chemistry differs between parent material, but is inconclusive for grape juice chemistry.
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