Thesis (MSc) -- University of Stellenbosch, 2005. / ENGLISH ABSTRACT: The Rooibos tea plant (Aspalathus linearis) is indigenous to South Africa and occurs
only in the Western Cape's Cedarberg region. Rooibos tea is produced from the
leaves and fine stems of the plant. The tea is normally prepared by brewing the leaves
and consuming the liquor. However, the Rooibos plant is not only used to prepare
tea; the plant extracts are also used in various neutraceutical and pharmaceutical
products, including health drinks, iced tea, soaps and moisturising creams.
Although the tea plant contains native enzymes responsible for the colour and aroma
development of Rooibos tea, the disruption and maceration of the plant material
during processing is insufficient to allow these enzymes proper access to the
substrates responsible for Rooibos tea's characteristics. The current processing of
Rooibos tea is also time consuming and is done under uncontrolled conditions,
leading to unnecessary loss in aroma and antioxidant content. The addition of
enzymes could improve the maceration of the plant material, shorten the processing
time and improve the extraction of aroma, colour and antioxidant components.
During this study, 16 commercially available microbial enzymes were evaluated on
three different Rooibos substrates for the improvement of aroma and colour
development, as well as the extraction of soluble solids (SS) and total polyphenols
(TP). Thirteen enzymes were evaluated on spent tea for the enhanced extraction of
soluble solids and to determine the best candidates for further evaluation on fermented
and green Rooibos tea. Seven of the enzymes improved the yield in SS from spent
tea. Up to 232% improvement was obtained, depending on the type of enzyme and
dosage applied.
The best six enzyme preparations were further evaluated on fermented Rooibos tea.
For Depol™ 670L at 20 ul/g tea, the laboratory treatment increased the yield in SS by
44%, while small-scale industrial simulations increased the SS by 26%. However, an
increase in the yield in SS was usually accompanied by a decrease in the %TP/SS
ratio, indicating that mainly inactive compounds were extracted. Based on the results
with the commercial enzymes, twelve "synthetic" enzyme cocktails, consisting of different combinations of commercial enzymes were designed, of which three
cocktails released increased amounts of SS without decreasing the %TP/SS ratio
significantly.
Thirteen enzymes were evaluated on dried and freshly cut green Rooibos tea, with
three enzymes (Depol™ 670L, Pectinex Ultra SP-L and Depol™ 692L) increasing the
yield in SS between 21% and 66%, and the TP content between 11% and 47%.
Laccase was the best candidate in improving colour development from green tea, with
the improvement being slightly better at 50°C than at 40°C.
All the "synthetic" cocktails containing laccase improved the colour extract of all
three substrates evaluated, but also significantly decreased the TP and antioxidant
content. However, lower dosages of laccase resulted in colour development with little
loss in the antioxidant content. Due to the promising results obtained with the
treatments of Rooibos tea with laccases, it was decided to clone and express the
laccase gene (lacA) of Pleurotus ostreatus into Aspergillus niger. The gene was
successfully transformed into A. niger, but the expression of the recombinant gene
was not effective. / AFRIKAANSE OPSOMMING: Die Rooibostee plant (Aspalathus linearisi is inheems tot Suid-Afrika en kom slegs in
die Sederberg-omgewing in die Wes-Kaap voor. Rooibostee word van die blare en
fyn stingels van die plant geproduseer. Die tee word normaalweg voorberei deur die
blare in kookwater te laat trek en dan die aftreksel te drink. Die Rooibos plant word
nie net gebruik om tee te maak nie; die tee ekstrak word ook gebruik vir verskeie
neutraseutiese en farmaseutiese produkte, insluitende gesondheidsdrankies, ystee,
seep en bevogtigingsrome.
Ten spyte daarvan dat die teeplant sy eie ensieme vir die kleur en aroma ontwikkeling
van Rooibostee bevat, is die verbreking en maserasie van die plantmateriaal tydens
prosessering onvoldoende om die ensieme genoeg toe gang tot die substrate
verantwoordelik vir die kenmerkende eienskappe van Rooibostee te gee. Die huidige
prosessering van Rooibostee is ook tydrowend en geskied onder onbeheerde
toestande, wat tot 'n onnodige verlies in aroma en antioksidante lei. Die toevoeging
van ensieme kan die afbraak van die plantmateriaal verbeter, die behandelingsproses
verkort en die aroma, kleur en antioksidant inhoud van ekstrakte verbeter.
Tydens hierdie studie is 16 kommersieel-beskikbare mikrobiese ensieme op drie
verskillende Rooibos substrate vir die verbetering van aroma, kleur en ekstraksie van
oplosbare vastestowwe (SS) en totale polifenole (TP) getoets. Dertien ensieme is op
oorskot tee vir die verbeterde ekstraksie van oplosbare vastestowwe geevalueer,
waama die beste kandidate vir evaluering op gefermenteerde en ongefermenteeede
Rooibostee gekies is. Sewe ensieme het die SS vanaf oorskot tee verhoog. Tot 232%
verhoging is waargeneem, afhangende van die tipe ensiem en die dosis wat gebruik is.
Die beste ensiern preparate IS verder op gefermenteerde Rooibostee geevalueer,
Labarotoriurn behandelings met Depol™ 670L teen 20 ul/g tee het die SS inhoud met
44% verhoog, terwyl die kleinskaalse industriele simulasie die SS inhoud met 26%
verhoog het. 'n Verhoging in SS het egter gewoonlik met 'n afname in die %TP/SS
verhouding gepaard gegaan, wat aandui dat hoofsaaklik onaktiewe stowwe vrygestel
IS. Na aanleiding van die resultate met die kommersiele ensieme, is twaalf "sintetiese" ensiemmengsels met verskillende ensiemkombinasies getoets, waarvan
drie mengsels ook meer SS vrygestel het met byna geen verlaging in die %TP/SS
verhouding nie.
Dertien ensieme was op gedroogde en vars gekerfde groen Rooibostee getoets met
drie ensieme (Depol™ 670L, Pectinex Ultra SP-L en Depol™ 692L) wat die SS met
tussen 21% en 66%, en die TP inhoud met tussen 11% en 47% verhoog het. Lakkase
was die beste kandidaat vir die verbetering van kleur ontwikkeling by groen
Rooibostee met die verbetering effens beter by 50°C as by 40°C.
Al die "sintetiese" ensiem mengsels wat lakkase bevat het, het die kleur by al die
verskillende substrate verbeter, maar het ook die TP en antioksidant inhoud aansienlik
verlaag. Laer lakkase dosisse het goeie kleurontwikkeling tot gevolg gehad met
minimale verlies in die antioksidant inhoud. Vanwee die goeie resultate wat met die
lakkase behandelings verkry is, is daar besluit om die lakkase geen (lacA) van
Pleurotus ostreatus te kloneer en in Aspergillus niger uit te druk. Die geen is
suksesvol in A. niger getransformeer, maar die uitdrukking daarvan was nie effektief
nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/50343 |
| Date | 04 1900 |
| Creators | Coetzee, Gerhardt |
| Contributors | Bloom, M., Van Zyl, W. H., Stellenbosch University. Faculty of Science. Dept. of Microbiology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 114 p. : ill. |
| Rights | Stellenbosch University |
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