Thesis (MScFoodSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The flavanone aglycones, hesperetin and eriodictyol, have been identified as potential taste modulators
with reported sweetness-enhancing and bitterness-masking properties, respectively. Reduction of the
sugar content of food products has become important in view of the global obesity epidemic. Taste
modulators have shown potential to enhance the sweet taste of reduced-sugar foods without
unfavourably affecting their flavour profile. On the other hand, bitterness-masking taste modulators are
useful to mask the bitter taste of functional phytochemical ingredients. In the current study, Cyclopia
maculata (honeybush) was investigated as potential source of hesperetin- and eriodictyol-enriched
extracts. Hesperetin and eriodictyol were present mainly below the quantification limit in C. maculata
plant material, including unfermented leaf and stem material, unfermented and fermented tea, as well as
the fermented by-product (< 40 mesh and > 12 mesh). Conversely, their rutinoside and modulatinginactive
derivatives, hesperidin and eriocitrin were present at substantially higher concentrations in the
plant material. The stems and by-product were shown to be good sources of hesperidin, but not
eriocitrin. The qualitative and quantitative phenolic profile of the by-product was similar to that of the
stems. The tea processing by-product was therefore selected to optimise extraction of flavanone
glycosides for subsequent de-glycosylation of the flavanone glycosides to aglycones.
The by-product was subjected to ultrasound-assisted extraction to investigate its potential as
renewable source of the flavanone glycosides. Response surface methodology (RSM) was employed to
optimise and study the individual and interactive effects of the process variables, namely ethanol
concentration (% v/v), time (min), temperature (°C), and solvent:solid ratio (mL/g), on flavanone
glycoside extraction. The hesperidin yield and content (of extract), as well as extract yield, increased with
an increase in extraction time, temperature and solvent:solid ratio. Practical process restrictions limited
global optimisation and only an optimum of 52.8% (v/v) ethanol for extract and hesperidin yield could be
reached. Temperature was the parameter with the most significant effect (p < 0.05) on extraction
efficiency among those studied. Practical process parameter values that were feasible for industrial
application (52.8% (v/v) ethanol, 20 mL/g solvent:solid ratio, 60°C and 30 min) were selected for the
preparation of a flavanone glycoside-enriched extract from the tea processing by-product. The flavanone glycoside-enriched extract was subjected to acid-catalysed hydrolysis to deglycosylate
hesperidin and eriocitrin to hesperetin and eriodictyol, respectively. RSM was employed to
optimise the acid hydrolysis process and to study the effect of the hydrolysis parameters (temperature
(°C) and time (min)) on hydrolysis efficiency. At the maximum temperature (92.1°C) and corresponding
optimum time (98.4 min) ca 80% conversion of hesperidin to hesperetin was achieved. Substantially more
eriodictyol formed during acid hydrolysis than eriocitrin present in the initial extract owing to the deglycosylation
of unidentified glycosides with the same aglycone. Unidentified breakdown products
imparting a red colour to the acid-hydrolysed extract were also observed. The total phenolic content of the acid-hydrolysed extract was significantly higher (p < 0.05) than that of the unhydrolysed extract,
indicating the formation of unidentified compounds with the ability to reduce the Folin-Ciocalteau
reagent, although no significant difference (p ≥ 0.05) between the antioxidant activities of these extracts,
as assessed with the DPPH radical scavenging and ORAC assays, was observed. The potential of enzymatic
bioconversion as an alternative to acid-catalysed hydrolysis was investigated using commercial
hesperidinase. Bioconversion resulted only in de-rhamnosylation with ca 100% conversion of hesperidin
to hesperetin-7-O-glucoside in an aqueous C. maculata extract at pH 4.0 and 40°C. / AFRIKAANSE OPSOMMING: Die flavanoon aglikone, hesperetien and eriodiktiol, is geïdentifiseer as potensiële smaakmoduleerders
met berigte soetheid-versterkende en bitter-maskerende eienskappe, onderskeidelik. Vermindering van
die suikerinhoud van voedselprodukte het belangrik geword in die lig van die wêreldwye vetsugepidemie.
Smaakmoduleerders het die potensiaal getoon om die soet smaak van voedsel met verlaagde
suikerinhoud te versterk sonder om hul geurprofiel ongunstig te beïnvloed. Andersyds is bittermaskerende
smaakmoduleerders nuttig om die bitter smaak van funksionele fitochemiese bestanddele te
maskeer. In die huidige studie is Cyclopia maculata (heuningbos) ondersoek as ‘n potensiële bron van
hesperetien- and eriodiktiol-verrykte ekstrakte. Hesperetien and eriodiktiol was hoofsaaklik teenwoordig
onder die kwantifiseringsperk in C. maculata plantmateriaal, insluitend ongefermenteerde blaar- en
stokmateriaal, ongefermenteerde en gefermenteerde tee, asook die gefermenteerde byproduk (< 40
maas en > 12 maas). Hierteenoor was hul rutinosiedes en modulerend-onaktiewe derivate, hesperidien
and eriositrien, teenwoordig in aansienlik hoër konsentrasies in die plantmateriaal. Die stokmateriaal en
byproduk is getoon om goeie bronne van hesperidien, maar nie eriositrien nie, te wees. Die kwalitatiewe
en kwantitatiewe fenoliese profiel van die byproduk was soortgelyk aan dié van die stokke. Die teeprosesseringsbyproduk
is dus geselekteer om die ekstraksie van flavanoonglikosiede, voorafgaande hul
de-glikosilering na aglikone, te optimeer.
Die byproduk is aan ekstraksie met behulp van ultrasoniese klank onderwerp om die potensiaal
daarvan as hernubare bron van flavanoonglikosiede te ondersoek. Respons-oppervlak Metodologie
(ROM) is gebruik om die individuele en wisselwerking effekte van die proses veranderlikes, naamlik
etanolkonsentrasie (% v/v), tyd (min), temperatuur (°C), en oplosmiddel:vastestof verhouding (mL/g), op
flavanoonglikosied ekstraksie te optimiseer en te bestudeer. Die hesperidienopbrengs en -inhoud (van
ekstrak), sowel as die ekstrakopbrengs, het toegeneem met ‘n toename in die ekstraksietyd, -
temperatuur en oplosmiddel:vastestof verhouding. Praktiese prosesbeperkings het die globale
optimisering beperk en slegs ‘n optimum van 52.8% (v/v) etanol vir ekstrak- en hesperidienopbrengs kon
bereik word. Temperatuur was die parameter met die mees beduidende effek (p < 0.05) op ekstraksie
doeltreffendheid van dié wat bestudeer is. Praktiese prosesparameterwaardes wat haalbaar is vir
industriële toepassing (52.8% (v/v) etanol, 20 mL/g oplosmiddel:vastestof verhouding, 60°C en 30 min) is
geselekteer vir die voorbereiding van 'n flavanoonglikosied-verrykte ekstrak uit die teeprosesseringsbyproduk. Die flavanoonglikosied-verrykte ekstrak is aan suur-gekataliseerde hidrolise onderwerp om
hesperidien en eriositrien na hesperetien en eriodiktiol, onderskeidelik, te de-glikosileer. ROM is gebruik
om die suurhidrolise proses te optimeer en die effek van die hidrolise parameters (temperatuur (°C) en
tyd (min)) op hidrolise doeltreffendheid te bestudeer. Ongeveer 80% omskakeling van hesperidien na
hesperetien is behaal teen die maksimum temperatuur (92.1 °C) en ooreenstemmende optimum tyd (98.4 min). Aansienlik meer eriodiktiol is tydens suurhidrolise gevorm as eriositrien wat in die
oorspronklike ekstrak teenwoordig was, as gevolg van de-glikosilering van ongeïdentifiseerde glikosiede
met dieselfde aglikoon. Ongeïdentifiseerde afbreekprodukte, wat 'n rooi kleur aan die suurgehidroliseerde
ekstrak gegee het, is ook waargeneem. Die totale fenoliese inhoud van die suurgehidroliseerde
ekstrak was beduidend hoër (p < 0.05) as dié van die ongehidroliseerde ekstrak, wat die
vorming van onbekende verbindings met die vermoeë om die Folin-Ciocalteau reagens te reduseer
aandui, hoewel daar geen beduidende verskil (p ≥ 0.05) tussen die antioksidant-aktiwiteite van hierdie
ekstrakte, soos bepaal met die DPPH radikaal blussings- en ORAC toetse, waargeneem is nie. Die
potensiaal van ensiematiese bio-omskakeling as 'n alternatief vir suur-gekataliseerde hidrolise is
ondersoek met behulp van kommersiële hesperidinase. Bio-omskakeling het slegs tot de-ramnosilering
gelei met ca 100% omskakeling van hesperidien na hesperetien-7-O-glukosied in 'n C. maculata
waterekstrak by pH 4.0 en 40°C.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/86260 |
| Date | 04 1900 |
| Creators | Du Preez, Brigitte Von Pressentin |
| Contributors | De Beer, D., Joubert, E., Muller, M., Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xv, 207 p. : col. ill |
| Rights | Stellenbosch University |
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