Characterisation of the sensory profile of Cyclopia intermedia and optimisation of fermentation parameters for improved product quality By Alexandra Jane Bergh Thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Food Science Department of Food Science, Faculty of AgriSciences, Stellenbosch University Supervisor: Prof E. Joubert ARC Infruitec-Nietvoorbij, Stellenbosch Co-supervisor: M. Muller Department of Food Science, Stellenbosch University December 2014 Stellenbosch University http://scholar.sun.ac.za DECLARATION By submitting this thesis electronically, I declare that the entirety of the work contained therein is my own, original work, that I am the sole author thereof (save to the extent explicitly otherwise stated), that reproduction and publication thereof by Stellenbosch University will not infringe any third party rights and that I have not previously in its entirety or in part submitted it for obtaining any qualification. Alexandra Jane Bergh December 2014 Copyright © 2014 Stellenbosch University All rights reserved i Stellenbosch University http://scholar.sun.ac.za ABSTRACT In light of the limited and inconsistent supply of good quality honeybush tea, a species-specific sensory profile and the physicochemical characteristics of Cyclopia intermedia (honeybush) tea were determined to ultimately establish the optimum fermentation parameters for this herbal tea on laboratory-scale and to validate these findings on commercial-scale. The characteristic sensory profile of C. intermedia can be described as sweet tasting and slightly astringent with a combination of “fynbos-floral”, “fynbos-sweet”, “fruity” (specifically “apricot jam”, “cooked apple”, “raisin” and “lemon/lemon grass”), “woody”, “caramel/ vanilla” and “honey-like” aromas. The flavour can be described as distinctly “fynbos-floral”, “fynbos-sweet” and “woody”, including hints of “lemon/lemon grass” and “hay/dried grass”. The results of the sensory study were used to create a C. intermedia sensory wheel and lexicon, and an elementary grading system that categorised samples into “good”, “average” and “poor” sensory quality was proposed. Physicochemical parameters, i.e. soluble solids (SS) content, absorbance as a measure of colour, and turbidity, were evaluated as possible rapid predictors of sensory quality. High SS content, absorbance and turbidity correlated strongly with “poor” sensory quality. A linear relationship existed between the physicochemical parameters. The effect of fermentation temperature (70, 80 and 90°C) and time (12, 16, 24, 36, 48 and 60 h) on the sensory and physicochemical characteristics of C. intermedia was determined on laboratory-scale. Increasing fermentation time increased the intensity of positive sensory attributes, while decreasing the intensity of negative sensory attributes. The SS content, colour and turbidity of infusions decreased with increasing fermentation time, while the SS content and turbidity of infusions increased with increasing fermentation temperature. Fermentation at 90°C for 36 h on laboratory-scale produced C. intermedia with the best sensory properties, while preserving the SS content and colour of infusions. Fermentation at 70°C and 80°C required longer fermentation times for development of positive sensory attributes. Fermentation at 90°C was subsequently validated on commercial-scale. Laboratory-scale fermentation of the same batches of plant material was also carried out concurrently to allow direct comparison of the scale of fermentation on tea quality. Commercial-scale fermentation, despite increased variability as a result of increased batch volumes and heating difficulties, produced C. intermedia of “good” sensory quality after 24 and 36 h of fermentation. Increasing fermentation time had little effect on the SS content and colour of infusions of tea produced on commercial-scale, but turbidity increased significantly after 36 h. Thus, to produce C. intermedia with consistently good quality on commercial-scale, fermentation at 90°C for 24 to 36 h is recommended. Increasing fermentation time past 48 h should be avoided to prevent turbidity and the development of sensory attributes characteristic of over-fermented tea. However, due to the large variability of commercial-scale honeybush tea production, it is recommended that each batch be monitored between 24 and 36 h to determine when optimum fermentation has been obtained. ii Stellenbosch University http://scholar.sun.ac.za UITTREKSEL Beperkte en wisselvallige beskikbaarheid van goeie gehalte heuningbostee noodsaak die optimisering van fermentasie parameters vir Cyclopia intermedia. Optimisering van fermentation parameters is op laboratorium skaal gedoen, gevolg deur validasie van die parameters op kommersiële skaal. Vooraf is die spesie-spesifieke sensoriese profiel en die fisies-chemiese eienskappe van C. intermedia tee bepaal. Die kenmerkende sensoriese profiel van C. intermedia kan beskryf word as soet en effens vrank met 'n kombinasie van "fynbos-blomagtige", "fynbos-soet", "vrugtige" (spesifiek "appelkooskonfyt", "gekookte appel", "rosyntjie” en “suurlemoen/sitroen gras"), "houtagtige", "karamel/vanilla" en "heuningagtige" aromas. Die smaak kan beskryf word as "fynbos-blomagtig", "fynbos-soet" en "houtagtig", met 'n tikkie "suurlemoen/sitroen gras" en "hooi/gedroogde gras". Die resultate van die sensoriese studie is gebruik om 'n C. intermedia sensoriese wiel en leksikon, asook 'n basiese graderingstelsel wat tee monsters in "goeie", "gemiddelde" en "swak" sensoriese kwaliteit klassifiseer, te ontwikkel. Fisies-chemiese parameters: oplosbare vastestof (SS) inhoud; absorbansie as 'n maatstaf van kleur; en troebelheid, is geëvalueer as moontlike indikasies van sensoriese kwaliteit. Hoë SS inhoud, absorbansie en troebelheid waardes het sterk met "swak" sensoriese kwaliteit gekorreleer. 'n Lineêre verwantskap bestaan tussen die fisies-chemiese parameters en kwaliteit. Die effek van fermentasie temperatuur (70, 80 en 90°C) en -tyd (12, 16, 24, 36, 48 en 60 h) op die sensoriese en fisies-chemiese eienskappe van C. intermedia is op laboratorium skaal bepaal. Verlenging van fermentasie tyd het die intensiteit van die positiewe sensoriese eienskappe verhoog, terwyl dit die intensiteit van negatiewe sensoriese eienskappe verminder het. Die SS inhoud, kleur en troebelheid van die tee het met verlengde fermentasie tyd afgeneem, terwyl die SS inhoud en troebelheid met verhoging van fermentasie temperatuur toegeneem het. Fermentasie by 90°C vir 36 h op laboratorium skaal het tee met die beste sensoriese eienskappe geproduseer, met behoud van die SS inhoud en kleur. Fermentasie by 70°C en 80°C het 'n langer fermentasie tyd vir die ontwikkeling van positiewe sensoriese eienskappe vereis. Fermentasie by 90°C is daaropvolgens op kommersiële skaal uitgevoer, met gelyktydige laboratorium skaal fermentasie van dieselfde plantmateriaal lotte om die direkte effek van die skaal van fermentasie op tee kwaliteit te bepaal. Kommersiële fermentasie, ten spyte van verhoogde wisselvalligheid as gevolg van groot volumes tee en probleme met verhitting, het tee van "goeie" sensoriese kwaliteit na fermentasie periodes van 24 en 36 h geproduseer. Verlenging van fermentasie tyd het min uitwerking op die SS inhoud en kleur van kommersiel gefermenteerde tea gehad, maar troebelheid het beduidend na 36 h toegeneem. Fermentasie by 90°C vir 24 - 36 h word gevolglik aanbeveel om tee met goeie gehalte op kommersiële skaal te produseer. Fermentasie vir langer as 48 h moet vermy word om troebelheid te voorkom en die ontwikkeling van sensoriese eienskappe kenmerkend van oor-gefermenteerde tee te vermy. As gevolg van faktore wat groot variasie in kommersiële skaal heuningbostee produksie kan teweegbring, word aanbeveel dat elke produksielot tussen 24 en 36 h gemonitor word om die optimum fermentasie tyd te bepaal. iii Stellenbosch University http://scholar.sun.ac.za ACKNOWLEDGEMENTS I would like to express my sincere gratitude to the following individuals for their invaluable contribution in helping me complete this study: My supervisors, Prof Joubert and Ms Muller, for their guidance, assistance, motivation and stimulation; Lené Erasmus, for your friendship and unrivalled assistance; George Dico and John Achilles, for their assistance, willingness to help and friendliness; Marita van der Rijst, for statistical analysis of my data; The sensory panel, for their interest and dedication; Other consultants, Martin Bergh and Colette Cronje, for bringing this study into fruition, and your guidance and assistance in the commercial sphere; Johann Kritzinger, for accommodating me at your processing plant and willingness to help; The staff and fellow post-graduate students at the Department of Food Science and Agricultural Research Council, for their help and support. iv Stellenbosch University http://scholar.sun.ac.za NOTES This thesis is presented in the format prescribed by the Department of Food Science, Stellenbosch University. The structure is in the form of two research chapters and is prefaced by an introduction chapter with the study objectives, followed by a literature review chapter and culminating with a general discussion and conclusions. Language, style and referencing format used are in accordance with the requirements of the International Journal of Food Science and Technology. This thesis represents a compilation of manuscripts where each chapter is an individual entity and some repetition between chapters has, therefore, been unavoidable.