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Development of a machine vision based oyster meat sorterKoslav, Maria B. January 1989 (has links)
Oyster meats are currently sorted by hand using volume as the sorting parameter. Hand grading is inaccurate, time consuming and costly. Previous research on physical properties of oyster meats showed a high correlation between projected area of oyster meats and their volume thus allowing the use of projected area measurements as a sorting criterion. A machine vision based oyster meat sorting machine was developed to mechanize the sorting process. The machine consists of a dark conveyor belt transporting singulated oysters through a grading station and then along a row of fast acting water jet valves which separates the stream of oysters into 3 classes. The vision system consists of a monochrome television camera, flash light illumination to "freeze" the images, a digitizer/transmitter and a Personal Computer as an image processing unit. Software synchronizes the flash light and digitization of images and calculates projected area of each meat using the planimeter method. The grading results are sent to a valve control board which actuates the spray valves. The sorting rate is 37 oyster meats/min with a sorting accuracy of 87.5%. A description of the design work, adjustment and l calibration procedures and a final sorting test is included. / Master of Science
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The use of purified enzymes for the early assessment of toxicityPfaff, John F. January 1982 (has links)
The increasing level and dispersion of toxic chemicals in the environment has stimulated a need for accurate methods capable of detecting and quantifying the activity of toxicants. The primary objective of this study was to determine, through in vitro tests, the potential of three purified enzymes: α-chymotrypsin, acid phosphatase, and carbonic anhydrase for use in the early assessment of toxicants at environmentally significant levels. Activities of α-chymotrypsin and acid phosphatase were measured spectrophotometrically, while carbonic anhydrase activities were determined through monitoring a pH change. The chemical agents investigated included several heavy metals, common herbicides and pesticides, and various environmentally significant anions. In addition, several techniques were explored to amplify enzyme response to chemical agents.
The results of the study demonstrated that α-chymotrypsin did not significantly respond to cadmium, nickel, or 2,4-D, and consequently, does not appear to be useful in indicating potential toxicity problems associated with these agents.
The acid phosphatase enzyme system appears to be useful in signaling the presence of low levels of certain anions (fluoride at 0.45 mg/ℓ and nitrate at 7.3 mg/ℓ), but does not appear to have potential for detecting toxic activity due to cadmium, nickel, or 2,4-D. Enzyme inhibition induced by fluoride at 37°C was not altered by changing the assay temperature to 50°C.
The results of the experiments with carbonic anhydrase show that the enzyme does not appear to be affected by cadmium or nickel ions. However, enzyme activity was inhibited by fluoride (4.5 mg/ℓ), sulfide (0.5 mg/ℓ), and nitrate (73 mg/ℓ). Enzyme inhibition was also induced by 10 mg/ℓ of atrazine, malathion, or carbaryl, and 150 to 500 mg/ℓ of 2,4-D. Inhibitory effects induced by sulfanilamide appeared to be slightly enhanced by the addition of Cd²⁺, Ni²⁺, or Zn²⁺ cations. These findings, although preliminary, suggest that carbonic anhydrase demonstrates potential for signaling the presence of anions, and appears to be useful in indicating potential toxicity problems due to pesticides and herbicides. / Master of Science
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Modeling of high fluence Ti ion implantation and vacuum carburization in steelRangaswamy, Mukundhan January 1985 (has links)
Concentration-versus-depth profiles have been calculated for Ti and C in Ti-implanted 52100 steel. A computer formalism was developed to account for diffusion and mixing processes, as well as sputtering and lattice dilation. A Gaussian distribution of Ti was assumed to be incorporated at each time interval. The effects of sputtering and lattice dilation were then included by means of an appropriate coordinate transformation. C was assumed to be gettered from the vacuum system in a one-to-one ratio with the surface Ti concentration up to a saturation point. Both Ti and C were allowed to diffuse. A series of experimental (Auger) concentration-versus-depth profiles of Ti implanted steel were analyzed using the above-mentioned assumptions. A best fit procedure for these curves yielded information on the values of the sputtering yield, range and straggling, as well as the mixing processes that occur during the implantation. The effective diffusivity of Ti was found to be 6x10⁻¹⁵ cm²/sec, a value that is consistent with the cascade mixing mechanism. The effective diffusivity of C was found 6x10⁻¹⁵ cm²/sec, and the sputtering yield by Ti atoms was best fit by a value of about 2. The observed range and straggling values were in very good agreement with the values predicted by existing theories, so long as the lattice was allowed to dilate. / M.S.
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Symbolic and computational conjugate geometry for design and manufacturing applicationsVoruganti, Ravinder Srinivas 03 March 2009 (has links)
Development of a methodology of applying symbolic and computational models of conjugate geometry to several problems in design and manufacturing areas forms the basis of this study. The philosophy of this work is the development of generalized symbolic models for two-dimensional and three-dimensional conjugate geometry applications. The generalized models have been implemented using what seems to be the best tool for these kind of applications - a symbolic manipulation system. The unique feature of this research is reflected in the fruitful combination of the elegance of conjugate geometry theory and the inherent versatility of a symbolic manipulation system.
The generalized conjugate geometry algorithms were programmed and run using MACSYMA. Typical cases in design of mechanisms have been studied using these symbolic programs. The manufacture of helically swept surfaces is of special interest to this work. Helically swept surfaces have been designed and three schemes of manufacturing these surfaces are presented here. Examples of these three schemes of manufacturing helically swept surfaces have been carried out using the symbolic program in MACSYMA. The results of all the examples have been presented both analytically and graphically. / Master of Science
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A study for the development of a laser tracking system utilizing multilateration for high accuracy dimensional metrologyGreeff, Gabriel Pieter 03 1900 (has links)
MScEng / Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Accurate dimensional measurement devices are critical for international industrial
competitiveness for South Africa. An overview of all the necessary
components of a laser tracking system using a multilateration technique for
very accurate dimensional metrology is presented.
A prototype laser tracker station was built to further investigate this type
of system. The prototype successfully tracks a target within a volume of at
least 200 200 200 mm3, approximately 300 mm away from the tracker.
This system includes the mechanical design of a prototype tracker station,
electronic implementation of ampli cation and motor control circuits, a tracking
control algorithm, microcontroller programming and interfacing, as well as
a user interface.
Kinematic modelling along with Monte Carlo analyses nd the main error
source of such a tracker as the beam steering mechanism gimbal axes misalignment.
Multilateration is also motivated by the results found by the analysis.
Furthermore, an initial sequential multilateration algorithm is developed
and tested. The results of these tests are promising and motivate the use of
multilateration over a single beam laser tracking system. / AFRIKAANSE OPSOMMING: Dit is van kritieke belang dat Suid-Afrika akkurate dimensionele metingstoestelle
ontwikkel vir internasionale industriële medinging. 'n Oorsig van al die nodige
komponente vir 'n Laser-Volgsisteem, wat slegs van multilaterasie gebruik
maak om baie akkurate drie dimensionele metings te kan neem, word in hierdie
projek voorgestel.
'n Prototipe Laser-Volgsisteem-stasie word gebou om so 'n sisteem verder
te ondersoek. Die prototipe slaag wel daarin om 'n teiken, binne 'n volume
van 200 200 200 mm3 op 'n afstand van omtrent 300 mm te volg. Die
sisteem sluit die meganiese ontwerp van die sodanige stasie, elektroniese seinversterking,
motorbeheer, 'n volgingsbeheer algoritme, mikroverwerker programeering
en intergrasie, asook 'n gebruikerskoppelvlak program in.
Kinematiese modelering, tesame met Monte Carlo simulasies, toon aan dat
die hoof oorsaak van metingsfoute by so 'n stasie by die rotasie-asse van die
laserstraal-stuurmeganisme, wat nie haaks is nie, lê. Die multilaterasie metode
word ook verder ondersteun deur dié modelering.
'n Algoritme wat sekwensiële multilateratsie toepas word boonop ontwikkel
en getoets. Die resultate van die toetse dui daarop dat die algoritme funksioneer
en dat daar voordele daarin kan wees om so 'n metode in plaas van 'n
Enkelstraal-Volgsisteem te gebruik.
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Innovative Duplex Filter for Hydraulic ApplicationsMössinger, Klaus 27 April 2016 (has links) (PDF)
For decades, duplex filters have been put to use virtually unmodified. Technologies, handling and use of materials show enormous potential for improvement. Filter element emoval/replacement is performed according to a complex process sequence. With the newly developed Duplex Filter, the market demands concerning simple filter element removal/replacement, as well as weight and pressure loss reduction are fully met.
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An experimental study of an inherently-safe, natural circulating, flash-tube type system for a nuclear reactor steam supply conceptLoubser, Karl Albie 12 1900 (has links)
Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: This project investigates aspects of a novel inherently safe nuclear power steam
supply system as safety is of paramount importance. The system envisaged has
unique features namely: a) a two-phase flow flash-tube type natural circulating
primary loop (also the secondary radioactive particle containment); b) a twophase
flow thermosyphon heat pipe type heat exchanger secondary loop is
used to transfer heat from the primary loop to the steam generators, thereby
physically separating the two flow streams from one another; c) a natural
convection air cooled condenser for the removal of the reactor’s residual heat;
d) a unique core using TRISO type fuel (acting as the primary radioactive
particle containment) with life of at least 8.9 years; e) a steel containment vessel
acting as a tertiary radioactive product containment; f) a concrete containing
structure with air vents to allow air to pass over the main steel containment
vessel for cooling purposes in the case of an emergency, and for the removal of
parasitic heat during operation.
In particular the primary and secondary loops of the proposed system are
investigated. This is done by design, construction and testing of a small scale
experimental set-up of the primary and secondary loops as well as the development
of theoretical models for the two loops. A literature survey focusing on
nuclear technology, thermosyphon loops, natural circulating loop instabilities,
heat pipes, and two-phase flow modelling is presented to give a brief overview
of the technologies as well as tools used in the work undertaken.
Observations of the inside flow behaviour of the primary loop experimental
set-up were made possible by windows providing many insights into the inner
workings, such as plume formation and geysering. The transient response of
the secondary heat pipe loop start-up is also investigated.
A thermal resistance theoretical model was developed for the secondary
loop using heat transfer formulae from theory as well as experimentally semiempirical
correlated formula. Different states of operation of the secondary
loop were observed during testing with the theoretical model of the condensing regime correlating well, two-phase regime correlating acceptably and liquid
regime correlating poorly to experimental results and thus were modelled using
an experimentally determined overall heat transfer coefficient. The secondary
loop model of the liquid regime is coupled with the primary loop theoretical
model to predict the system’s performance.
A homogeneous, one-dimensional, simple theoretical model for the primary
loop was derived and computer simulated. The results did not compare well
with experimental results for single phase flow and failed to capture the onset
of two-phase flow. The assumptions of one dimensional model with a unidirectional
flow, a hydrostatic pressure problem, a constant volumetric flow rate
and the inability of the implementation of the code to handle expansion are
noted as some of the flaws in the theoretical model.
The following recommendations are made: a more advanced design of the
pressuriser should be incorporated into the experiment; the secondary loop’s
theoretical model should be characterised under a broader set of operating
conditions; the computer program can be used as the basis for further research
and implementation of alternative solution algorithms and models. / AFRIKKANSE OPSOMMING: Hierdie projek ondersoek aspekte van ’n ongewone, essensieel veilige kernkrag
stoomtoevoer-stelsel, omdat veiligheid van kardinale belang is. Die stelsel wat
voorgestel is, het unieke eienskappe, naamlik: a) ’n twee-fasevloei flits-buistipe
natuurlik sirkulerende primêre lus (wat ook die sekondêre inperking van
radioaktiewe materiaal bevat); b) ’n twee-fasevloei termo-heweleffek sekondêre
lus hitte-pyp hitte-uitruiler word gebruik om die hitte vanaf die primêre lus
oor te dra na die stoomkragopwekkers en daardeur word die twee strome se
vloei fisies geskei van mekaar; c) ’n natuurlike konveksie lugverkoelde kondensor
word gebruik vir die verwydering van die reaktors se oortollige hitte; d) ’n
unieke kern gebruik TRISO-tipe brandstof (wat as die primêre inperking van
radioaktiewe materiaal optree) met ’n lewe van minstens 8.9 jaar; e) ’n inperkingshouer
van staal wat optree as ’n tersiêre radioaktiewe produkhouer; f) ’n
betonstruktuur met lugventilasie om toe te laat dat lug oor die hoof staalhouer
vloei vir verkoeling in ’n noodgeval, en vir die verwydering van parasitiese hitte
tydens werking.
Hoofsaaklik word die primêre en sekondêre lusse van die voorgestelde stelsel
ondersoek. Dit word gedoen deur die ontwerp, konstruksie en die toets
van ’n eksperimentele opstelling van die primêre en sekondêre lusse op klein
skaal, sowel as die ontwikkeling van teoretiese modelle vir die twee lusse. ’n Literatuurstudie
wat fokus op kerntegnologie, termo-heweleffeklusse, natuurlik
sirkulerende lus instabiliteit, hitte-pype, en twee-fase vloeimodellering word
aangebied om ’n kort oorsig te gee van die tegnologie, sowel as gereedskap
gebruik in die werk wat onderneem is.
Om die interne vloeigedrag van die primêre lus se eksperimentele opstelling
waar te neem, word daar gebruik gemaak van vensters wat dien as ’n manier
om die innerlike werking van die proses soos pluimvorming en die kook van die water in die warmwaterkolom te toon. Die oorgangsreaksie van die sekondêre
hittepyplus aanvangs is ook ondersoek.
’n Teoretiese termiese weerstandmodel is ontwikkel vir die sekondêre lus
met behulp van hitte-oordragformules waarvoor hitte-oordragteorie gebruik
is, wat met eksperimentele semi-empiriese formules gekorreleer is. Verskillende
toestande van die sekondêre lus se werking is waargeneem gedurende die toetse.
Die teoretiese model het goed met die kondensasiestaat gekorreleer, terwyl by
die twee-fasewerkswyse aanvaarbare korrellasies aangetref is en die uiteindelike
vloeitoestand swakker gekorrelleer het met eksperimentele resultate en dus
gemodelleer is met behulp van die NTU-effektiwiteitsmetode. Die sekondêre
lusmodel van die vloeistoftoestand is gekoppel met die primêre lus teoretiese
model om die werking van die stelsels te voorspel.
’n Homogene een-dimensionele eenvoudige teoretiese model van die primêre
lus is afgelei en ’n rekenaar simulasie is uitgevoer. Die resultate vergelyk nie
goed met die eksperimentele resultate vir enkelfasevloei en kon nie die aanvang
van twee-fasevloei beskryf nie. Die aannemings van ’n een-dimensionele
model met eenrigting vloei, ’n hidrostatiese druk probleem, ’n konstant volumetries
vloeitempo en die onvermoë van die implementering van die kode
om uitbreiding te hanteer is bekend as ’n paar van die foute in die teoretiese
model.
Die volgende aanbevelings word gemaak: ’n meer gevorderde ontwerp van
drukreëlaar moet in die eksperiment ingesluit word; die sekondêre lus se teoretiese
model moet gekenmerk word onder ’n wyer stel bedryfsomstandighede,
en die rekenaar program kan gebruik word as die basis vir verdere navorsing
en die implementering van alternatiewe algoritmes en modelle.
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The effect of exogenous protease on the relative enzyme activity of β-glucosidase in oenological conditionsSwart, Elsa Marita 12 1900 (has links)
Thesis (MScAgric)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The distinctive varietal flavour of wines is a combination of absolute and relative
concentrations of chemical compounds. Volatile compounds are responsible for the
odour of wine and non-volatiles cause the sensation of flavour. Accompanying these
senses, a third, tactile, sense of ‘mouth-feel’ is recognizable. This forms the complete
organoleptic quality of wine.
Several hundred different compounds are simultaneously responsible for the
odour release in wine, and since there is no real character impact compound, the
aroma of wine can be described as a delicate balance of all these compounds. One
of the most important groups of volatiles is the monoterpenes, which play a role in
both aroma and flavour. This is especially significant for the Muscat varieties, but
these flavour compounds are also present in other non-muscat grape varieties,
where they supplement the varietal aroma. Monoterpenes occur in wine as free,
volatile and odorous molecules, as well as flavourless non-volatile glycosidic
complexes. The latter slowly releases monoterpenes by acidic hydrolysis, but the
impact on varietal aroma is considered insufficient for wines that are consumed
young. It is therefore important to supplement the release mechanism, in order to
enhance the varietal aroma of the wine. The enzymatic hydrolysis mechanism
functions in two successive steps: firstly, depending on the precursor, the glycosidic
linkage is cleaved by α-L-arabinofuranosidase, α-L-rhamnosidase, β-D-xylosidase or
β-D-apiosidase. The second step involves the liberation of the monoterpene alcohol
by a β-glucosidase. This enzymatic hydrolysis does not influence the intrinsic
aromatic characteristics of the wine, as opposed to acid hydrolysis.
Pectolytic enzymes play an important role in cell elongation, softening of tissue
and decomposition of plant material. These enzymes are used to improve juice
yields, release colour and flavour compounds from grape skins, as well as improve
clarification and filterability. Pectolytic enzymes work synergistically to break down
pectins in wine. Protopectinase produce water-soluble and highly polymerised pectin
substances from protopectin, it acts on non-methylated galacturonic acid units. Pectin
methylesterase split methyl ester groups from the polygalacturonic chain.
Polygalacturonase break down the glycosidic links between galacturonic acid units.
Pectin and pectate lyases have a β-eliminative attack on the chain and it results in
the formation of a double bond between C4 and C5 in the terminal residues.
From the above it can be seen that enzymes play a pivotal role in the
winemaking process. Unfortunately, in winemaking a lot of factors can influence the
effects of enzymes. One possible factor in the wine medium is the presence of acidprotease,
from yeast and/or fungal origin. This type of enzyme utilizes other enzymes
as substrates and renders them useless. Pure enzyme preparations were used to
study the interactions of a yeast acid-protease and a report activity (β-glucosidase) in
vitro. A bottled wine and a buffer were used as in vitro conditions. Enzyme assays were performed to determine the relative activity over a number of days. The results
indicated that even though both enzymes showed activity in both the media, the
yeast protease did not have any significantly affect on the report activity.
Subsequently wine was made from Sauvignon blanc grapes, with varying enzyme
preparation additions. Enzyme assays were performed during the fermentation; and
chemical, as well as sensory analysis were done on the stabilized wine. The results
confirmed that the yeast protease did not have any significant affect on the report
activity in these conditions. The protease’s inability to affect the report activity seems
unlikely due to the fact that it is active at a low pH range and has been suggested as
the only protease to survive the fermentation process. It seems possible that a winerelated
factor, possibly ethanol, is responsible. Thus it seems that yeast protease
does not threaten the use of commercial enzymes in the winemaking process in any
significant way.
Future work would entail more detailed enzyme studies of interactions
between protease, both from yeast and fungal origin, and other report activities in
specified conditions. The degradation capability could be directed towards unwanted
enzyme activities that cause oxidation and browning of the must. The
characterization of interactions between protease and β-glucosidase activities may
hold key to producing wines with enhanced aroma and colour potential, as well as
the elimination of unwanted enzyme activities. / AFRIKAANSE OPSOMMING: Die herkenbare kultivar karakter van wyn is ‘n kombinasie van absolute en relatiewe
konsentrasies van verskeie chemiese komponente. Vlugtige komponente is
verantwoordelik vir die geur, of aroma, van wyn en die nie-vlugtige komponente
veroorsaak die sensasie van smaak. ‘n Derde, fisiese sensasie, die ‘mondgevoel’, is
ook herkenbaar. Dit vorm die omvattende organoleptiese kwaliteit van die wyn.
‘n Paar honderd verskillende komponente is gelyktydig verantwoordelik vir die
aroma vrystelling in wyn en omdat daar geen werklike karakter ‘impak’ komponent is
nie, kan die aroma van wyn beskryf word as ‘n delikate balans van al die betrokke
komponente. Een van die mees belangrike groepe vlugtige komponente is die
monoterpene wat ‘n rol speel in beide aroma en smaak. Dit is veral belangrik by
Muskaat kultivars, maar hierdie aroma komponente is ook teenwoordig in niemuskaat
druif kultivars, waar hulle bydra tot die kultivar karakter en aroma.
Monoterpene kom in wyn voor as vry, vlugtige en aromatiese molekules en in
geurlose, nie-vlugtige glikosidies-gebonde komplekse. Die gebonde vorm word stadig
vrygestel deur ‘n suurhidrolise, maar dit word as onvoldoende beskou vir wyne wat
vroeg gedrink word. Dit is dus belangrik dat die vrystelling van geurstowwe verhoog
word om die kultivar karakter van die wyn te versterk. Die ensiematiese hidrolise
proses behels twee opeenvolgende stappe: eerstens, afhangende van die aard van
die voorloper, word die glikosidiese verbinding deur α-L-arabinofuranosidase, α-Lramnosidase,
β-D-xilosidase, of β-D-apiosidase gebreek. In die tweede stap word die
monoterpeen-alkohol deur β-glukosidase vrygestel. Hierdie ensiematiese afbraak
proses verander nie die intrinsieke aromatiese kenmerke van die wyn, soos met
suurhidrolise die geval is nie.
Pektolitiese ensieme speel ‘n fundamentele rol in selverlenging, sagwording en
afbraak van plant materiaal. Hierdie ensieme word gebruik om sap opbrengs te
verhoog, aroma en smaak komponente vry te stel uit die doppe, asook om
sapverheldering en filtrasie te verbeter. Die pektolitiese ensieme werk op ‘n
sinergistiese wyse om pektien in wyn af te breek. Protopektinase produseer wateroplosbare
en hoogs gepolimeriseerde pektien uit protopektien, slegs uit niegemetileerde
galakturoonsuur eenhede. Pektien metielesterase verwyder metielester
groepe van die poligalakturoonsuurketting. Die glikosidiese bindings tussen
galakturoonsuur eenhede word deur poligalakturonase afgebreek. Pektien- en
pektaat-liase het ‘n β-eliminasie aanslag op die ketting en as gevolg daarvan word
dubbelbindings tussen C4 en C5 in die terminale residue gevorm.
Vanuit bogenoemde is dit dus duidelik dat ensieme ‘n kardinale rol speel in die
wynbereidingsproses. Ongelukkig is daar ‘n verskeidenhied van faktore wat die
werking van ensieme in die wynbereidingsproses kan beïnvloed. Een moontlike
faktor is die teenwoordigheid van ‘n suur-protease, van fungisidiese en/of gis
oorsprong, in die wynmedium, omdat dit ander ensieme as substraat kan benut en degradeer. Suiwer ensiem preparate is gebruik om die ensiem interaksie tussen ‘n
gis suur-protease en ‘n verslag aktiwiteit (β-glukosidase) in vitro te ondersoek. ‘n
Gebotteleerde wyn en ‘n buffer is gebruik om die in vitro kondisies na te boots.
Relatiewe ensiem aktiwiteit is ontleed oor ‘n aantal dae. Beide die ensieme het
aktiwiteit getoon in die media, maar gis protease het geen statisties beduidende
invloed gehad op die aktiwiteit van die verslag ensiem nie. Daaropvolgend is wyn
berei van Sauvignon blanc druiwe, met verskillende ensiempreparaat toevoegings.
Die ensiemaktiwiteit is deurlopend tydens fermentasie gemeet. Na afloop van
stabilisasie is chemiese, sowel as sensoriese ontledings op die wyn gedoen. Die
resultate het bevestig dat gis protease, onder hierdie kondisies, geen beduidende
invloed op die verslag aktiwiteit gehad het nie. Die protease se onvermoë om die
verslag aktiwiteit beduidend te beinvloed blyk onwaarskynlik aangesien die suurprotease
aktief is by lae pH vlakke en dit as die enigste protease voorgestel is wat
die fermentasie proses kan oorleef. Dit blyk asof ‘n wyn-verwante faktor, moontlik
etanol, hiervoor verantwoordelik kan wees. Dus hou protease geen gevaar in vir die
gebruik van kommersiële ensieme in wynbereiding nie.
Navorsing kan in die toekoms fokus op meer gedetailleerde ensiem interaksie
studies tussen protease en ander ensiem aktiwiteite, in gespesifiseerde kondisies.
Die degradasie kapasiteit kan moontlik aangewend word om ongewenste ensiem
aktiwiteite, wat byvoorbeeld oksidasie en verbruining veroorsaak, te verminder. Die
karakterisering van die interaksies tussen protease en β-glukosidase kan dus die
sleutel wees tot die produksie van wyne met verhoogde aroma potensiaal, asook die
eliminasie van ongewenste ensiematiese aktiwiteite.
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Co-expression of aroma liberating enzymes in a wine yeast strainDe Klerk, Daniel 03 1900 (has links)
Thesis (Msc (Viticulture and Oenology. Institute for Wine Biotechnology))--University of Stellenbosch, 2009. / Monoterpenes are important aroma compounds in certain grape varieties such as Muscat, Gewürztraminer and Riesling and are present as either odourless, glycosidically bound complexes or as free aromatic monoterpenes. These complexes occur as monoglucosides or, when present as diglycosides, most commonly as 6-O-α-L-arabinofuranosyl-β-D-glucopyranosides of mainly linalool, geraniol, nerol and citronellol.
The release of monoterpenes from non-volatile glycosidically bound precursors occurs either by acid hydrolysis or enzymatic hydrolysis. High temperature acid hydrolysis causes a rearrangement of the monoterpene aglycones and a decrease in the aroma and changes in the aromatic characteristics of monoterpenes and is therefore not suitable. Enzymatic hydrolysis does not modify the monoterpene aglycones and can be an efficent method to release potentially volatile monoterpenes.
α-L-arabinofuranosidase and β-glucosidase are important enzymes responsible for the liberation of monoterpene alcohols from their glycosides. Glycosidases from Vitis vinifera and Saccharomyces cerevisiae are severely inhibited by winemaking conditions and this leads to unutilized aroma potential, while commercial preparations of aroma liberating enzymes are crude extracts that often have unwanted and unpredictable side effects. It is therefore of interest to investigate alternative measures to release glycosidically bound monoterpenes to increase the floral aroma of wine without side activities that impact negatively on wine.
Heterologous α-L-arabinofuranosidases and β-glucosidases have previously been expressed in S. cerevisiae and these studies have evaluated and found increased glycosidic activities against both natural and synthetic substrates.
In this study, we expressed the Aspergillus awamori α-L-arabinofuranosidase (AwAbfB) in combination with either the β-glucosidases Bgl2 from Saccharomycopsis fibuligera or the BglA from Aspergillus kawachii in the industrial yeast strain S. cerevisiae VIN13 to facilitate the sequential enzymatic hydrolysis of monoterpene diglycosides. Enzyme assays and GC-FID (Gas Chromatography with a Flame Ionization Detector) results show a significant increase in the amount of free monoterpene concentrations under winemaking conditions in the strain co-expressing the AwAbfB and the Bgl2. The increases in free monoterpene levels obtained were similar to those obtained with a commercial enzyme preparation, LAFAZYM AROM. Sensorial evaluation confirmed the improvement in the wine aroma profile, particularly the floral character. This yeast strain permits a single culture fermentation which improves the sensorial quality and complexity of wine. Further investigations on the factors influencing the stability and reactivity of monoterpenes during alcoholic fermentation are needed.
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Impact of low-frequency high-power ultrasound on spoilage and potentially pathogenic dairy microbesCameron, Michelle 12 1900 (has links)
Thesis (PhD (Food Science))--University of Stellenbosch, 2007. / Thermal pasteurisation failures in the dairy industry have often been found to cause
end-products of poor quality and short shelf-life. Therefore, alternative methods to
eliminate microbial contaminants in raw milk are being studied. Ultrasonication is one
such non-thermal technology that could offer the dairy industry an alternative to
traditional pasteurisation.
The main objective of this dissertation was to evaluate the use of high-power lowfrequency
ultrasound (20 kHz, 750 W, 124 μm) applied in batch mode to eliminate a
selection of spoilage and potentially pathogenic microbes, commonly associated with
milk. These included Gram-positive and negative microbes, comprising of rods and
cocci, an endospore-former, and a yeast (Escherichia coli, Bacillus cereus,
Chryseobacterium meningosepticum, Lactobacillus acidophilus, Lactococcus lactis,
Listeria monocytogenes, Micrococcus luteus, Pseudomonas fluorescens and
Saccharomyces cerevisiae).
Three strains of E. coli (1 x 106 cfu.ml-1) tested, viz. ATCC 11775, a wild strain
from raw milk, and an O157:H7 strain from milk were sensitive to ultrasonication.
Complete elimination of viable cells occurred within 10 min. Viable counts of
P. fluorescens were reduced by 100% within 6 min of ultrasonication and
L. monocytogenes was reduced by 99.0% within 10 min. Lactococcus lactis was
reduced by 97.0% and M. luteus, B. cereus and C. meningosepticum by 88.0%, 87.0%
and 85.0% respectively. Lactobacillus acidophilus showed the most resistance to
ultrasound with only 78.0% of viable cells being eliminated. Under similar conditions,
S. cerevisiae was reduced by 99.7%. Microbial cell morphology, size and Gram status
did not necessarily influence the efficacy of ultrasonication. Sterile saline solution and
UHT milk were used as the suspension media, and the reputed protective effect of milk
fat was not observed under the parameters used in this study. A higher wave amplitude
(100%; 124 μm) was found to be more efficient in eliminating microbes than a lower
wave amplitude (50%; 62 μm). Pulsed-ultrasonication did not enhance the efficiency of
ultrasonication indicating that standing waves were absent.
Limited success was achieved by ultrasonication itself, and the long batch
treatment time (10 min or more) was found to be unrealistic for industrial
implementation. Hence the simultaneous application of ultrasound and heat (thermoultrasonication)
was examined. Thermo-ultrasonication proved to be more effective than either an ultrasonic or
heat treatment with all viable M. luteus cells being eliminated within 4 min (100%
amplitude at 72°C). Similarly, to eliminate E. coli and Lb. acidophilus from milk, only 2
min and 4 min thermo-ultrasonication was required, respectively. Bacillus cereus
endospores remained resistant and after a 10 min thermo-ultrasonic treatment only
78.04% were eliminated.
During this investigation both extensive surface (SEM) and internal (TEM) cell
damage caused by ultrasonication were observed in E. coli, Lb. acidophilus and
S. cerevisiae. Hence ultrasonication physically/mechanically damages these microbial
cells causing cell death/injury.
Microbial proteins and DNA released from cells into the environment after an
ultrasonic treatment was measured and an increase in released microbial proteins and
DNA was found to be indicative of a decrease in the number of viable cells, providing
that the initial cell concentration was high enough. It was, however, not possible to
correlate the concentration of released microbial proteins and DNA with the exact
number of viable cells eliminated, rendering it an ineffective quality indicator for the
industry.
Ultrasonication had no statistically significant influence on the protein, fat and
lactose content of both raw and pasteurised milk. The somatic cell count of raw and
pasteurised milk was found to decrease after ultrasonication. Unlike with heating,
activity of alkaline phosphatase and lactoperoxidase were not reduced by
ultrasonication. Hence neither enzyme can be used to indicate a successful ultrasonic
treatment of milk.
This study has demonstrated that ultrasonication offers a viable alternative to
pasteurisation as it is effective in eliminating microbes, and does not alter native milk
components. However, to attain a more effective killing, thermo-ultrasonication is
recommended for the treatment of milk to be used for the production of different dairy
products.
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