Sensory and phenolic profiling of Cyclopia species (Honeybush) and optimisation of the fermentation conditions

Theron, Karin Alicia (2012-03)

Thesis (MSc Food Sc)--Stellenbosch University, 2012.


ENGLISH ABSTRACT: The sensory profiles, phenolic composition and colour of honeybush infusions, prepared from six Cyclopia species (C. sessiliflora, C. longifolia, C. genistoides, C. intermedia, C. subternata and C. maculata), were determined to establish the variation between species. The results of the sensory study were used to create a honeybush sensory wheel and lexicon. The “characteristic” sensory profile of honeybush tea can be described as a combination of floral, sweet, fruity and plantlike flavours with a sweet taste and a slightly astringent mouthfeel. Sensory results indicated that the species could be divided into three distinct groups; group A (C. sessiliflora, C. intermedia and C. genistoides), group B (C. longifolia and C. subternata) and group C (C. maculata). Group A was associated with fynbos floral, fynbos sweet and plantlike attributes, group B with rose geranium and fruity sweet attributes and group C with woody, boiled syrup and cassia/cinnamon attributes. Gas chromatography-olfactometry analysis of the C. maculata aroma fraction indicated that the spicy note of its aroma could possibly be explained by the high concentration of the volatile component eugenol. However, none of the aroma impact volatiles had a specific cassia/cinnamon note. Large variation in the composition of the honeybush infusions was revealed through the quantification of the soluble solids, total polyphenol and individual monomeric polyphenolic compounds, as well as the absorbance (“colour”). Infusions of C. genistoides, C. longifolia and C. sessiliflora had the highest soluble solids and total polyphenol content, as well as the highest absorbance values. Only mangiferin, isomangiferin, hesperidin and compound C (unidentified compound) were detected in all six Cyclopia species. Cyclopia genistoides, C. longifolia and C. sessiliflora, in order of prominence, contained the highest concentration of both mangiferin and isomangiferin whereas C. genistoides and C. maculata contained the highest hesperidin content. The bitter taste present in certain Cyclopia species appeared to be due to a high mangiferin content, however, compounds such as isomangiferin and compound C might also have played a role. The effect of fermentation (oxidation) temperature (80°C and 90°C) and time (8 h, 16 h, 24 h and 32 h) of C. genistoides, C. subternata and C. maculata on the sensory characteristics of their infusions was also investigated. Fermentation for longer than 8 h resulted in an increase in positive sensory attributes and a decrease in negative sensory attributes rather than the formation of new sensory attributes. A fermentation temperature/time combination of 80°C/24 hours or 90°C/16 h was required for C. genistoides, C. subternata and C. maculata. Fermenting C. genistoides at 90°C would result in a honeybush infusion with slightly less rose geranium notes whereas C. subternata can be fermented at either 80°C or 90°C, depending on whether floral or apricot jam notes are desired. Cyclopia maculata should preferably not be fermented at 90°C due to an increase in negative sensory attributes (hay/dried grass and green grass). Fermentation reduced the soluble solids content, total polyphenol content, colour and concentration of individual polyphenolic compounds. Changes in the taste and mouthfeel of honeybush tea could be attributed to changes in the polyphenolic composition caused by the high temperature oxidation. Mangiferin associated with the bitter taste of C. genistoides, while in C. subternata astringency may be partly attributed to the mangiferin and isomangiferin content. The study substantiated the need for further research on the contribution of the major phenolic compounds towards the taste and mouthfeel of Cyclopia species.

AFRIKAANSE OPSOMMING: Die sensoriese profiel, fenoliese samestelling en kleur van heuningbostee, berei van ses Cyclopia spesies (C. sessiliflora, C. longifolia, C. genistoides, C. intermedia, C. subternata en C. maculata), is bepaal ten einde die mate van variasie vas te stel. Die resultate van die sensoriese studie is gebruik om 'n sensoriese wiel en leksikon vir heuningbostee te ontwikkel. Die “karakteristieke” sensoriese profiel van heuningbostee kan beskryf word as 'n kombinasie van blomagtig, soet, vrugtig en plantagtige geure met 'n soet smaak en 'n effense frankheid. Sensoriese resultate het aangedui dat die spesies in drie groepe verdeel kon word; groep A (C. sessiliflora, C. intermedia and C. genistoides), groep B (C. longifolia and C. subternata) en groep C (C. maculata). Groep A is met fynbos blom, fynbos-soet en plantagtige geure geassosieer, groep B met roos geranium en vrugtige-soet geure en group C met houtagtige, gekookte stroop en kassia/kaneel geure. Gaschromatografie-olfaktometrie analises van C. maculata se aroma fraksie het getoon dat die speseryagtige aroma moontlik as gevolg van die hoë konsentrasie van die vlugtige komponent, eugenol, kon wees. Geen van die aroma-impak vlugtige verbindings het egter 'n spesifieke kassia/kaneelagtige noot gehad nie. Groot variasie in die samestelling van heuningbostee ten opsigte van die inhoud van oplosbare vastestowwe, totale polifenole en monomeriese fenoliese verbindings, asook die absorbansie (“kleur”) is aangetoon. Heuningbostee berei van C. genistoides, C. longifolia en C. sessiliflora het die hoogste oplosbare vastestowwe en totale polifenol inhoud, asook die hoogste absorbansie waardes gehad. Slegs mangiferien, isomangiferien, hesperidien en verbinding C (ongeïdentifiseerde verbinding) is in al ses Cyclopia spesies geïdentifiseer. Cyclopia genistoides, C. longifolia en C. sessiliflora, in volgorde van belangrikheid, het die hoogste konsentrasie van beide mangiferien en isomangiferin gehad teenoor C. genistoides en C. maculata wat die hoogste hesperidien konsentrasie gehad het. Die bitter smaak teenwoordig in sekere Cyclopia spesies blyk moontlik as gevolg van die hoë mangiferien inhoud te wees, hoewel komponente soos isomangiferien en komponent C dalk ook 'n rol mag speel. Die effek van die fermentasie temperatuur (80°C en 90°C) en tyd (8 h, 16 h, 24 h en 32 h) van C. genistoides, C. subternata en C. maculata op die sensoriese eienskappe van heuningbostee is ondersoek. Fermentasie vir langer as 8 h het tot 'n toename in positiewe sensoriese eienskappe en afname in negatiewe sensoriese eienskappe gelei eerder as die ontstaan van nuwe sensoriese eienskappe. Om heuningbostee met 'n optimum sensoriese profiel te verkry is 'n fermentasie temperatuur/tyd kombinaise van 80°C/24 h of 90°C/16 h nodig vir C. genistoides, C. subternata en C. maculata. Cyclopia genistoides wat by 90°C gefermenteer word sal minder van die roos geranium note bevat, terwyl C. subternata by 80°C of 90°C gefermenteer kan word, afhangende of 'n blomagtige of 'n appelkooskonfyt noot verlang word. Fermentasie by 90°C word nie aanbeveel C. maculata nie as gevolg van die toename van sekere negatiewe sensoriese eienskappe (hooi/droe gras aroma en -geur en groen gras aroma). Fermentasie het die inhoud van oplosbare vastestowwe, totale polifenole, individuele polifenoliese verbindings, asook kleur verminder. Veranderinge in die smaak en mondgevoel van heuningbostee kon toegeskryf word aan die veranderinge in die polifenoliese inhoud as gevolg van die hoë temperatuur oksidasie. Mangiferien is met die bitter smaak van C. genistoides geassosieer, terwyl mangiferien and isomangiferien moontlik deels frankheid in C. subternata veroorsaak. Die studie het die noodsaaklikheid vir verdere navorsing op die bydrae van die hoof fenoliese verbindings tot die smaak en mondgevoel van Cyclopia spesies gestaaf.

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