Development of sensory tools for quality grading of Cyclopia genistoides, C. longifolia, C. maculata and C. subternata herbal teas

Erasmus, Lene Mari (2015-04)

Thesis (MSc Food Sc)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: The sensory profiles and the phenolic composition of C. genistoides, C. longifolia, C. maculata and C. subternata, used for commercial production of honeybush tea, were determined with the aim to develop quality control tools, such as sensory wheels and statistical models to predict the basic taste and mouthfeel modalities using compositional data. Optimum fermentation parameters for C. longifolia in terms of aroma and flavour development were determined by investigating eight temperature/time regimes (80°C and 90°C for 8, 16, 24 and 32 h), using descriptive sensory analysis (DSA). Fermentation at 80°C/24 h or 90°C/24 h significantly reduced the negative sensory attributes present and produced a tea of good sensory quality. Previously, 80°C/24 h and 90°/16 h were shown to deliver optimum quality for the other three Cyclopia species. A large sample set (N = 150) consisting of C. genistoides, C. maculata and C. subternata, harvested during three production years (2010, 2012 and 2013), as well as C. longifolia harvested in 2013, was used to develop sensory wheels. All the samples were produced by fermentation at the two optimum fermentation temperature/time regimes of each species. The plant material was sourced from different production regions and plantations to ensure inherent plant variation was accommodated. The “characteristic” and generic sensory profile of honeybush was defined as a “fynbos-floral”, “woody”, “fynbos-sweet” aroma and flavour, with a sweet taste and slightly astringent mouthfeel. Species-specific sensory profiles were also identified. Cyclopia genistoides had a strong “rose geranium” flavour and a perceptible bitter taste, whereas C. longifolia had a similar sensory profile to that of C. genistoides, however, C. longifolia’s “rose geranium” flavour was less prominent and its bitter taste not perceptible. Cyclopia maculata and C. subternata were both described as having “caramel” and other “sweet-associated” notes and a slightly astringent mouthfeel. These results were used to develop a generic sensory wheel for both aroma and flavour, as well as similar wheels for each of the four Cyclopia species. Each sensory wheel reflects the relative intensity of the sensory attributes, while prevalence of the major attributes were accommodated in accompanying bar graphs. Sorting was investigated as a rapid profiling technique to serve as an alternative to the standard profiling method, descriptive sensory analysis (DSA). Instructed sorting was identified as a possible rapid sensory profiling tool for the honeybush industry, especially when samples need to be classified according to a selected list of sensory attributes. Uninstructed sorting can be used when the aim is to categorise a group of samples freely according to similarities and thus determine the natural grouping of samples within a broader sample set. The phenolic content of the respective four Cyclopia species differed qualitatively and quantitatively. Of the compounds quantified only four compounds were present in all four species, i.e. hesperidin, vicenin-2, mangiferin and isomangiferin. A larger number of compounds were present in three out of four species. The predictive value of the phenolic compounds towards the intensity of the taste and mouthfeel attributes (sweet, sour, bitter and astringent) was investigated using Pearson‟s correlation analysis, partial least squares regression (PLS) and step-wise regression analysis. Potential “candidate predictors” for taste and mouthfeel attributes were identified such as the xanthones, mangiferin and isomangiferin, being responsible for bitter taste and astringency.

AFRIKAANSE OPSOMMING: Die sensoriese profiel en fenoliese samestelling van C. genistoides, C. longifolia, C. maculata en C. subternata, waarvan heuningbostee geproduseer word, is bepaal om gehaltebeheer hulpmiddels te ontwikkel soos sensoriese wiele en statistiese modelle wat die fenoliese samestelling kan gebruik om die basiese smaak en mondgevoel eienskappe van infusies te voorspel. Die optimum fermentasie parameters vir C. longifolia in terma van aroma- en geurontwikkeling is bepaal deur agt temperatuur/tyd kombinasies (80°C en 90°C vir 8, 16, 24 en 32 h) te ondersoek met behulp van beskrywende sensoriese analise (BSA). Fermentasie by 80°C/24 h of 90°C/24 h het „n beduidende afname in die negatiewe sensoriese eienskappe veroorsaak en tot die ontwikkeling van tee met ʼn goeie sensoriese kwaliteit gelei. Die fermentasie parameters, 80°C/24 h en 90°/16 h, is voorheen aangedui as die optimale kondisies vir die ontwikkeling van „n goeie kwaliteit tee vir die ander drie Cyclopia spesies. 'n Groot stel monsters (N = 150), bestaande uit C. genistoides, C. maculata en C. subternata en ge-oes gedurende drie produksiejare (2010, 2012 en 2013), sowel as C. longifolia ge-oes in 2013, is gebruik om die sensoriese wiele te ontwikkel. Die twee optimum fermentasie temperatuur/tyd kombinasies van elke spesie is gebruik om die monsters te produseer. Plantmateriaal afkomstig van verskillende produksiegebiede en plantasies is versamel ten einde te verseker dat die monsters „n betekenisvolle hoeveelheid inherente variasie dek. Die generiese en "karakteristieke" sensoriese profiel wat met heuningbos geassosieer word, is gedefinieer as 'n "fynbos-blomagtige", "houtagtige", "fynbos-soet" aroma en geur, met 'n soet smaak en effense vrank mondgevoel. Spesies-spesifieke sensoriese profiele is ook geïdentifiseer. Cyclopia genistoides het 'n sterk "roos malva" geur en „n merkbare bitter smaak. Die sensoriese profiel van C. longifolia is soortgelyk aan dié van C. genistoides, maar sy "roos malva" geur was minder prominent en 'n bitter smaak was nie sensories waarneembaar nie. Beide C. maculata en C. subternata het waarneembare "karamel" en ander "soet-verwante" eienskappe, asook 'n effense vrank mondgevoel getoon. Die volle stel data is uiteindelik gebruik om 'n generiese sensoriese wiel vir heuningbostee, asook spesies-spesifieke sensoriese wiele vir elk van die vier Cyclopia spesies saam te stel. Die onderskeie sensoriese wiele weerspieël die relatiewe intensiteit van elk van die sensoriese eienskappe, terwyl die voorkoms-frekwensie van die onderskeie sensoriese eienskappe in gepaardgaande kolomgrafieke geillustreer is. Sortering, 'n vinnige profileringsmetode, is as alternatief tot die standaard profileringsmetode, beskrywende sensoriese analise (BSA), ondersoek. Gestrukteerde sortering is geïdentifiseer as 'n moontlike hulpmiddel vir die heuningbosbedryf om die sensoriese profiel van heuningbos te bepaal, veral wanneer „n groot aantal monsters vinning geklassifiseer moet word volgens 'n lys geselekteerde sensoriese eienskappe. Ongestrukteerde sortering kan gebruik word wanneer die doel is om „n groot aantal monsters vrylik te kategoriseer volgens hul sensoriese ooreenkomste of verskille. Die fenoliese saamestelling van die vier Cyclopia spesies het kwalitatief en kwantitatief verskil. Slegs vier van die gekwantifiseerde verbindings was teenwoordig in al vier spesies, naamlik hesperidien, visenien-2, mangiferien en isomangiferien. Meer verbindings was egter teenwoordig in drie van die vier spesies. Die voorspellingswaarde van die fenoliese verbindings tot die intensiteit van die smaak en mondgevoel eienskappe (soet, suur, bitter en vrank) is ondersoek met behulp van Pearson se korrelasie, gedeeltelike kleinste-kwadrate regressie (PLS) en stapsgewyse regressie analises. Potensiële "kandidaat voorspellers" vir die smaak en mondgevoel eienskappe, soos die xantone, mangiferien en isomangiferien, verantwoordelik vir 'n bitter smaak en vrank mondgevoel, is geïdentifiseer.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/96756
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