Development and validation of prediction models and rapid sensory methodologies to understand intrinsic bitterness of Cyclopia genistoides

Moelich, Erika Ilette (2018-03)

Thesis (PhD (Food Sc))--Stellenbosch, 2018.

Thesis

ENGLISH ABSTRACT: Cyclopia species, endemic to South Africa, is used for the production of honeybush tea. This herbal tea has grown from a product consumed only locally to one currently marketed worldwide. Cyclopia species is high in polyphenols, well-known for its health related properties, but these compounds could contribute to bitterness, which may elicit negative consumer response. One of the species, C. genistoides, is high in polyphenols but also associated with bitterness, contrary to the characteristic sweet taste and honey-like flavour associated with honeybush. The polyphenolic content of four Cyclopia species were quantified with high-performance liquid chromatography diode-array detection while descriptive sensory analysis (DSA) was used to determine the taste intensities of these samples. The link between phenolic content and bitterness was investigated. Based in the phenolic content of C. genistoides and C. longifolia, partial least squares (PLS) regression analysis identified four compounds, mangiferin, isomangiferin, iriflophenone-3-C-glucoside-4-O-glucoside and iriflophenone-3-C-glucoside, as candidate predictors of bitterness. This model will find application as screening tool in cultivar development research programs. Production of honeybush lags behind demand, forcing the industry to use blends of Cyclopia species, including C. genistoides, to supply in the increased demand. The distinct differences in the sensory profiles associated with different Cyclopia species require that special care is given to blending to ensure a consistent, high quality product. DSA was used to evaluate the effect of blending of C. genistoides with other Cyclopia species on bitterness. Blending of C. genistoides with C. subternata, C. intermedia or C. maculata in a ratio of 2:3 were effective in reducing bitterness to below perceptible levels. The sensory profile of C. genistoides- C. subternata blends were further quantified using DSA and was described as “fynbos floral”, “apricot”, “woody”, “fruity sweet” and “fynbos sweet” aroma and a sweet taste. Based on these results, inclusion of C. genistoides at 40% when blending different Cyclopia species, is recommended. Blending at this standardised ratio will result in a well-rounded product with bitterness below perceptible levels. The herbal tea industry expressed the need for time- and cost-effective methods for sensory screening of infusions to improve quality and product consistency. The validity of three rapid profiling methods {sorting, projective mapping and polarised sensory positioning (PSP)} for the sensory characterisation of honeybush infusions were investigated using a trained panel. The efficacy of partial (aroma or palate attributes) or global (all attributes) evaluation was compared within each rapid method. Product configurations similar to that of DSA demonstrated the validity of all three methods for broad sensory profiling of Cyclopia species. Sorting on palate attributes resulted in additional differentiation between samples with only subtle differences. Sorting demonstrated to be the most effective method for the broad sensory profiling of honeybush infusions and could find application in the honeybush industry as screening tool. PSP on the other hand could find application in quality control programs where poles that represent specific quality attributes, should be included. Implementation of valid, scientific methods, such as sorting and PSP, will aid the honeybush industry in their effort to supply a product with consistent quality and high consumer appeal.

AFRIKAANSE OPSOMMING: Die eg Suid-Afrikaanse fynbosgenus, Cyclopia, word gebruik vir die produksie van heuningbostee, ‘n unieke kruietee wat internasionaal bemark word. Die gebruik van heuningbostee hou verskeie gesondheidsvoordele in wat grootliks toegeskryf kan word aan die fenoliese samestelling, maar hierdie verbindings kan bydra tot ‘n bitter smaak wat negatiewe verbruikersreaksie tot gevolg mag hê. Een van die spesies, Cyclopia genistoides, beskik oor ‘n hoë fenoliese samestelling, maar word ook met ‘n bitter smaak geassosieer. Die fenoliese samestelling van vier Cyclopia spesies is gekwantifiseer deur middel van hoë-druk vloeistof chromatografie gekoppel aan ultraviolet-diode deteksie. Beskrywende sensoriese analise is gebruik om die sensoriese profiel te kwantifiseer. Die verband tussen fenoliese samestelling en bitterheid is ondersoek. Die fenoliese samestelling van C. genistoides en C. longifolia is gebruik vir die ontwikkeling van ‘n model om bitterheid te voorspel. Gedeeltelike kleinste-kwadrate regressie analise (PLS) met seleksie van veranderlikes is op die data toegepas. Vier komponente, naamlik mangiferien, isomangiferien, iriflofenoon-3-C-glukosied- 4-O-glukosied en iriflofenoon-3-C-glukosied, is geïdentifiseer as potensiële “kandidaat voorspellers” vir bitterheid. Hierdie model kan toepassing vind in die heuningbos kultivar ontwikkelingsprogram vir die seleksie van plantmateriaal. Die vraag na heuningbos oorskry produksie, wat die bedryf noodsaak om Cyclopia spesies te vermeng. Beduidende verskille in die geurprofiel van die verskillende Cyclopia spesies vereis dat mengsels met omsigtigheid berei word om ‘n konstante, hoë kwaliteit eindproduk te verseker. Beskrywende sensoriese analise is gebruik om die effek van vermenging van C. genistoides met ander Cyclopia spesies op bitterheid te bepaal. Vermenging van C. genistoides met enige van C. subternata, C. intermedia of C. maculata in ‘n verhouding van 2:3 was effektief om bitterheid tot onder waarneembare vlakke te verlaag. Die sensoriese profiel van die C. genistoides-C. subternata mengsel kan beskryf word as ‘n “fynbos-blomagtige”, “appelkoos”, “houtagtige”, “vrugtige-soet” en “fynbos-soet” aroma en ʼn soet smaak. Op grond van hierdie resultate kan aanbevelings aan die heuningbosteebedryf gemaak word. Insluiting van C. genistoides teen 40% in Cyclopia mengsels sal ‘n produk met lae bitterheid en ‘n karakteristieke heuningbostee profiel lewer. Die heuningbosteebedryf is ‘n klein, maar groeiende bedryf en die implementering van tyd- en kosteeffektiewe metodes vir sensoriese evaluaring is belangrik. Hierdie studie het die geldigheid van drie vinnige profileringsmetodes {sortering, projektiewe kartering (PK) en gepolariseerde sensoriese posisionering (GSP)} vir die sensoriese beskrywing van heuningbostee, ondersoek. Die effektiwiteit van hierdie metodes, gefokus per modaliteit (aroma of geur) of met ‘n holistiese benadering, is vergelyk. Al drie die genoemde vinnige profileringsmetodes is geldige metodes vir die oorsigtelike sensoriese kategorisering van Cyclopia spesies. Addisionele differensiasie tussen produkte met slegs subtiele verskille is verkry deur sortering, gefokus op geur-eienskappe. Sortering is die mees effektiewe metode vir die oorsigtelike beskrywing van heuningbostee en kan effektief in die heuningbosteebedryf toegepas word. Verder kan GSP toepassing vind in kwaliteitsbeheerprogramme waar produkte met spesifieke eienskappe ingesluit word as verwysingstandaarde. Implementering van geldige en betroubare sensoriese metodes, soos sortering en GSP, kan ‘n waardevolle bydrae lewer in die heuningbosteebedryf om ‘n kwaliteit produk met hoë verbruikersaanvaarbaarheid te voorsien aan ‘n groeiende mark.

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