Thesis (MSc Food Sc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Application of steam treatment to green Cyclopia maculata and C. longifolia to modulate their aroma
and flavour profile, without detrimental effects on colour and individual phenolic content, was
investigated. Steam treatment (96 °C, atmospheric pressure) of different time periods was applied
to the shredded, fresh plant material before drying (STBD; 0, 30, 60, 90 and 120 s) or the herbal tea
product after drying (STAD; 0, 1, 2, 3, and 4 min). Steam treatment of 60 s or longer resulted in a
significant (p < 0.05) decrease in vegetative (‘green grass’ and ‘hay/dried grass’) and cereal
(‘oats/porridge/grains’) aroma and flavour intensities, with an increase in some fruity (‘tropical fruit’
and ‘guava’) and ‘fruity-sweet' aroma intensities. These changes manifested to a greater degree for
plant material subjected to STBD, while they were less prominent for C. longifolia compared to
C. maculata. Additionally, 19 aroma compounds were instrumentally identified in the volatile fraction
of C. maculata infusions prepared from STBD plant material. Of these, seven correlated well with
green honeybush vegetative and cereal aroma attributes associated with unsteamed samples.
Steaming thus resulted in the rapid loss of some of these highly volatile ‘green’-associated aroma
compounds. Steam treatment of more than 60 s, regardless of STBD or STAD, was not detrimental
to green colour, and individual phenolic content was not greatly affected. The 30 s STBD treatment
of C. maculata, however, led to the rapid loss of green colour and oxidation of phenolic compounds,
without considerable aroma improvement. This highlights the need for process control during green
honeybush production. Storage stability of steamed (60 s, STBD) and unsteamed green C. maculata was
investigated under low (0 °C; moisture impermeable packaging) and normal (25 °C at 60% relative
humidity (RH); semi-moisture-permeable sachets) temperature storage conditions (LTS and NTS,
respectively) over 6 months and high temperature storage (HTS) conditions (40 °C at 75% RH; semimoisture-
permeable sachets) for 1 month. HTS conditions, after 1 month, seemed to emulate
changes occurring over 6 months at NTS conditions, with little change detected at LTS conditions.
Despite noticeable green colour loss over the respective storage periods at NTS and HTS conditions,
individual phenolic compounds were not severely affected. NTS and HTS led to the progressive
development of sought-after fermented honeybush sensory attributes, especially in unsteamed
samples. These include prominent fruity (‘stewed fruit’, ‘apricot jam’ and ‘marmalade’) aromas and
flavours, ‘general sweet’ and ‘fruity-sweet’ aromas and a sweeter taste. The collated descriptive sensory data were used to generate a preliminary sensory wheel for
green honeybush aroma, and another for flavour, taste and mouthfeel. The sensory profile of green
honeybush was finally described as a dominant vegetative aroma and flavour, prominent sweetassociated
and slightly fruity aroma, with sweet and notably bitter tastes and an astringent mouthfeel.
By combining the sensory data, it was clear that the major effects of storage outweighed those of
steam treatments, suggesting that storage of 3 to 6 months may improve sensory quality, although colour may be slightly compromised. Immediate sensory manipulation and thus improvement,
however, may be achieved to a lesser degree in the short term by STBD. / AFRIKAANSE OPSOMMING: Die toepassing van stoombehandeling van groen Cyclopia maculata en C. longifolia vir die
modulasie van hul aroma en geur profiel, sonder gepaardgaande nadelige gevolge op kleur en
individuele fenoliese inhoud, is ondersoek. Stoombehandeling (96 °C, atmosferiese druk) van
verskeie tydstippe is toegepas op die gekerfde, vars plantmateriaal voor droging (SBVD; 0, 30, 60,
90 en 120 s) of die groen teeproduk ná droging (SBND; 0, 1, 2, 3 en 4 min). Stoombehandeling van
60 s of langer het tot 'n betekenisvolle (p < 0.05) afname in vegetatiewe (‘groen gras’ en
‘hooi/gedroogde gras’) en graan (‘hawer/pap/graan’) aroma en geur intensiteite gelei, met 'n
toename in sommige vrugtige (‘tropiese vrugte’ en ‘koejawel’) en ‘vrugtige-soet’ aroma intensiteite.
Hierdie veranderinge was meer merkbaar in die SBVD behandeling, terwyl C. longifolia minder
vatbaar vir hierdie veranderinge was as C. maculata. Daarbenewens is 19 aromaverbindings in die
vlugtige fraksie van C. maculata aftreksel voorberei van SBVD plantmateriaal instrumenteel
geïdentifiseer. Sewe hiervan het goed gekorreleer met heuningbos vegetatiewe en graan aromas
wat verband hou met ongestoomde monsters. Stoombehandeling het dus gelei tot die vinnige verlies
van sommige van hierdie baie vlugtige ‘groen’-geassosieërde aromaverbindings. Stoombehandeling
vir langer as 60 s, ongeag van SBVD of SBND, het nie die groen kleur en individuele fenoliese
inhoud grootliks nadelig beïnvloed nie. ‘n SBVD behandeling van 30 s het egter tot die vinnige verlies
van groen kleur en oksidasie van fenoliese verbindings, sonder aansienlike aroma verbetering van
C. maculata gelei. Dít beklemtoon die noodsaaklikheid vir prosesbeheer tydens groen
heuningbosproduksie. Stabiliteit van gestoomde (60 s, SBVD) en ongestoomde groen C. maculata tydens
opberging onder lae (0 °C; vog-ondeurlaatbare verpakking) en normale (25 °C by 60% relatiewe
humiditeit (RH); semi-vogdeurlaatbare sakkies) temperatuur opbergingtoestande (LTO en NTO,
onderskeidelik) oor 6 maande en hoë temperatuur opbergingtoestande (40 °C by 75% RH; semivogdeurlaatbare
sakkies; HTO) vir 1 maand, is ondersoek. HTO het na 1 maand soortgelyke
veranderinge teweeggebring as NTO na 6 maande, terwyl min verandering by LTO bespeur is. Ten
spyte van merkbare groen kleur verlies oor die onderskeie tydperke by NTO en HTO is individuele
fenoliese verbindings min beinvloed. NTO en HTO het gelei tot die progresiewe ontwikkeling van
gesogte sensoriese eienskappe van gefermenteerde heuningbos, veral in ongestoomde monsters.
Dit sluit in prominente vrugtige (‘gestoofde vrugte’, ‘appelkooskonfyt’ en ‘marmelade’) aromas en
geure , ‘algemene soet’ en ‘vrugtige-soet’ aromas en 'n soeter smaak. Al die beskrywende sensoriese data is saamgestel om 'n voorlopige sensoriese wiel vir groen
heuningbos aroma op te stel, asook een vir geur, smaak en mondgevoel. Die sensoriese profiel van
groen heuningbos kan beskryf word as 'n oorheersende vegetatiewe aroma en geur, prominente
soet-verwante en effens vrugtige aroma, met soet en veral bitter smaak en ‘n vrank mondgevoel.
Deur die sensoriese data te kombineer kon duidelik uitgewys word dat die belangrikste gevolge van
opberging dié van stoombehandeling oortref. Dit dui daarop dat opberging van 3 tot 6 maande sensoriese kwaliteit kan verbeter, hoewel kleur effens benadeel kan word. In die kort termyn kan
onmiddellike sensoriese manipulasie en dus verbetering egter in 'n mindere mate deur SBVD bereik
word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/97808 |
| Date | 12 1900 |
| Creators | Alexander, Lara |
| Contributors | Joubert, Elizabeth, Muller, Magdalena, De Beer, Dalene, 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 | xvii, 249 pages : colour illustrations |
| Rights | Stellenbosch University |
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