Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Aspalathus linearis is a leguminous shrub native to the Cedarberg Mountains in the Western
Cape, of which the leaves and stems are used for the preparation of rooibos tea. Over the past
few decades, rooibos tea and other related products have gained popularity due to their health
promoting properties. These beneficial properties can partly be ascribed to the phenolic
constituents that are trapped within the cellulolytic plant material of the tea leaves as
glycoconjugated aroma and phenolic compounds. Although many fungal species are known
for their efficient hydrolysis of plant material, fungal enzymes have not been evaluated for the
bioprocessing of rooibos tea to improve its commercial value. It was the objective of this
study to identify a specific cocktail of microbial enzymes to enhance the maceration of the
rooibos plant material, while retaining the antioxidant content.
During this study, 11 fungal species known for the production of hydrolytic enzymes,
as well as 12 species isolated from rooibos tea products, were screened for their potential to
improve aroma development and/or increased extraction of soluble matter and/or antioxidants
from rooibos tea material.
After culturing in Potato Dextrose medium, the crude enzyme extracts of the 23
isolates were evaluated on spent rooibos tea for enhanced extraction of soluble solids (SS)
and/or total polyphenols (TP). Nine strains increased the yield in SS (improvement varying
from 3% to 42%), while 14 strains yielded higher levels of TP (increase varying from 1% to
36%). Little improvement in colour development from green (unfermented) rooibos tea was
observed, but the enzyme extracts from Pleurotus ostreatus var. florida, Lentinula edodes,
Aspergillus oryzae, Aspergillus tubingensis, Paecilomyces variotti and Trichoderma reesei
improved the aroma development from green tea to some extent. Ten-fold concentrated
enzyme extracts from four of these isolates were able to release at least an additional 10% in
SS from the green tea.
The crude enzyme extracts prepared from three food-grade strains, i.e. Aspergillus
oryzae, Lentinula edodes and Pleurotus ostreatus var.florida, contained relatively high levels
of endoglucanase, xylanase and pectinase activities. Eight different culture media were
evaluated for optimal hydrolase and laecase production by these food-grade fungi. MYPG
proved to be the best growth medium, while 1% spent grain, 1% wheat straw and 1%
pineapple peel gave the best induction of xylanase, cellulase, pectinase and laecase activities
for L. edodes. When cultured in the Yeast Peptone (YP) medium + 1% wheat straw, the L. edodes
enzyme cocktail showed the best improvement in both the aroma and colour development of
green tea and may be considered for shortening of the fermentation time required for green tea
processing. Traditional open-air fermentation of rooibos tea can take up to -1-6hours, which
results in a significant loss in antioxidants and therefore also in its pharmaceutical and
nutraceutical value. The Rhizopus oryzae cocktail prepared in YP + 1% wheat straw showed
potential for the development of a quick-draw fermented tea made by infusion, where there is
improved colour release and more than 20% improved extraction of soluble solids without a
loss in the TP content.
When cultured in Potato Dextrose medium, the L. edodes cocktail can be used for
aroma and colour development from green tea, while the R. oryzae cocktail can be used for
increasing the antioxidant content in rooibos extracts from green or fermented tea. This was
confirmed with small-scale industrial treatments of fermented tea where the L. edodes YP +
wheat straw cocktail improved the release in SS by more than 10% and the R. oryzae yP +
wheat straw cocktail increased the yield in SS by more than 30% and the TP by more than
20%. / AFRIKAANSE OPSOMMING: Aspalathus linearis is 'n fynbosplant inheems aan die Sederberge in die Wes-Kaap, waarvan
die blare en stingels vir die voorbereiding van rooibostee gebruik word. Die afgelope paar
dekades het die gewildheid van rooibostee en verwante produkte aansienlik toegeneem weens
die gesondheidsvoordele wat dit inhou. Hierdie voordelige eienskappe kan toegeskryf word
aan die fenoliese komponente wat binne die sellulolitiese plantweefsel van die teeblare as
gekonjugeerde geur- en fenoliese verbindings vasgevang is. Alhoewel verskeie swamspesies
vir hul doeltreffende degradering van plantmateriaal bekend is, is fungale ensieme nog nie
geëvalueer vir die prosessering van rooibostee om die kommersiële waarde daarvan te
verbeter nie. Die doelwit van hierdie studie was om 'n spesifieke kombinasie van mikrobiese
hidrolitiese ensieme te identifiseer wat die maserasie van rooibos plantmateriaal sal verhoog
met behoud van die anti-oksidant inhoud.
Tydens hierdie studie is 11 swamspesies wat bekend is vir die produksie van
hidrolitiese ensieme, asook 12 swamspecies wat vanaf rooibostee produkte geïsoleer is,
geëvalueer vir hul potensiaalom geurontwikkeling en/of ekstraksie van oplosbare stowwe
en/of anti-oksidante vanuit rooibostee materiaal te verbeter.
Die kru ensiemekstrakte van die 23 isolate, wat ID Aartappel-Dextrose medium
opgegroei is, is op oorskot rooibostee geëvalueer vir verhoogde ekstraksie van oplosbare
vastestowwe (SS) en/of totale polifenole (TP). Nege rasse het die opbrengs van oplosbare
vastestowwe verhoog (verbetering tussen 3% en 42%), terwyl 14 rasse die totale polifenoliese
vlakke laat toeneem het (tot so hoog as 36%). Baie min verbetering in kleurontwikkeling van
groen (ongefermenteerde) rooibostee is waargeneem, maar ensiemekstrakte van Pleurotus
ostreatus var. florida, Lentinula edodes, Aspergillus oryzae, Aspergillus tubingensis,
Paecilomyces variotti en Trichoderma reesei, het wel die aroma ontwikkeling vanaf groen tee
tot 'n mate verbeter. Tienvoudig gekonsentereerde ekstrakte van vier van hierdie isolate het 'n
verbetering van meer as 10% in die ekstraksie van opgeloste vastestowwe uit groen tee tot
gevolg gehad.
Die ensiemekstrakte van drie swarnme bekend vir hul gebruik in die voedselindustrie,
nl. A. oryzae, L. edodes and P. ostreatus var. florida, het relatief hoë vlakke van
endoglukanase, xylanase en pektinase aktiwiteit getoon. Agt verskillende kultuur-media is vir
die optimale produksie van hidrolitiese and lakkase ensieme vanaf hierdie voedsel-graad
swarnme geëvalueer. MYPG was die beste groeimedium vir L. edodes, -terwyl 1% koringstrooi, 1% oorskot graan en 1% pynappelskil die beste induksie van xylanase,
pektinase, endoglukanase en lakkase aktiwiteite vir hierdie organisme getoon het. Lentinula
edodes opgegroei in YP medium + 1% koringstrooi, het die beste verbetering in aroma en
kleur getoon vanaf groen tee getoon. Hierdie ekstrak kan dus moontlik gebruik word vir die
verkorting van die fermentasietyd wat vir groen tee benodig word. Ope-lug fermentasie van
groen tee duur gewoonlik tot 16 uur en lei tot 'n aansienlike verlies in antioksidant-inhoud.
Die R. oryzae ekstrak het die beste potensiaal vir die vervaardiging van 'n "quick-draw" tee
getoon met 'n goeie kleurvrystelling sonder enige verlies in SS en TP opbrengs.
Wanneer die swamme in Aartappel-Dextrose medium opggegroei word, kan die
L. edodes ensiemekstrak vir aroma en kleurontwikkeling van groen tee aangewend word,
terwyl die R. oryzae ensiemekstrak vir die verhoging van die antioksidant-inhoud in rooibos
ekstrakte van groen tee of gefermenteerde tee gebruik kan word. Dit is bevestig met die
kleinskaalse behandeling van gefermenteerde tee waar die L. edodes YP + 1% koringstrooi
ensiemekstrak die vrystelling van SS met meer as 30% en die TP met meer as 20% verbeter
het.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/50342 |
| Date | 03 1900 |
| Creators | Pengilly, Mia |
| 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 | Unknown |
| Type | Thesis |
| Format | 144 p. : ill. |
| Rights | Stellenbosch University |
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