Development of a xanthone-enriched honeybush tea extract

Bosman, Stephanie Cesa (2014-12)

Thesis (MScFoodSc)--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: Cyclopia genistoides (honeybush) has been identified as an excellent resource for the production of a xanthone-enriched extract due to its high mangiferin content and successful cultivation. The predominant xanthone present in C. genistoides is mangiferin, a potent antioxidant proven to exhibit a wide range of bioactivities that contribute greatly to the health-promoting abilities of honeybush extracts. Isomangiferin, the regio-isomer of mangiferin and of comparable antioxidant capacity to mangiferin, is another valuable compound present in substantial quantities in C. genistoides. A xanthone-enriched extract would find possible application in functional food/beverage products that provide health benefits beyond basic nutrition. In the current study, the effect of ethanol (EtOH) concentration (0-100%, v/v), plant material size (milled vs. teabag fraction), extraction time (0-60 min) and elevated extraction temperatures on the extraction of xanthones from unfermented C. genistoides was investigated. Single factor experiments showed the best extraction efficiency, evaluated in terms of extract yield, xanthone yield and xanthone content of the extract, was achieved by extracting milled plant material with 20-60% EtOH (v/v) for 30 min at elevated temperatures (70°C). Response surface methodology (RSM) to evaluate the individual and interaction effects of process variables, namely EtOH concentration (0-100%, v/v) and temperature (0-70°C) was used to further optimise the extraction process. EtOH concentration was found to have the largest effect on extraction efficiency (p < 0.05), whilst temperature had a negligible effect. Optimal levels of EtOH concentration (40%, v/v) and temperature (70°C) for maximum extract and mangiferin yields were successfully achieved within the experimental domain, using 10 mL/g solvent:solid ratio and 30 min extraction time. Ultrafiltration (UF) was subsequently employed to facilitate further xanthone enrichment of the unfermented C. genistoides extract (40% EtOH, v/v). A series of laboratory scale membrane devices (centrifugal membrane units, stirred cell and tangential flow ultrafiltration (TFU) system) were used in an up-scale approach to determine the effect of membrane material (regenerated cellulose (RC) vs. polyethersulphone (PES)), molecular weight cut off (MWCO; 3 kDa, 10 kDa, 30 kDa), feed concentration (1% vs. 3% soluble solids (SS)) and operating parameters (transmembrane pressure (TMP) and feed flow rate) on membrane performance and permeate quality. The best performing membrane in terms of productivity and xanthone enrichment was the 10 kDa RC membrane when using an extract concentration close to that of industrially prepared extracts (3% SS). RSM was used to further optimise UF of unfermented C. genistoides through a 10 kDa RC membrane in the TFU system. The individual and interaction effects of TMP (0.82-2.04 bar) and feed flow rate (200-444 mL/min) on permeate flux, xanthone enrichment and the fouling index were investigated. The individual effects of TMP and feed flow rate had a significant effect on all measured responses, while their interaction only affected average permeate flux and fouling index significantly. Optimal TMP and feed flow rate values of 2.04 bar and 444 mL/min, respectively, were selected within the experimental domain, restricted by equipment constraints. Validation of the combined protocol including ethanol-water extraction and UF using plant material from ten different unfermented C. genistoides batches resulted in enriched extracts containing 10.6-17.8% xanthone content. During UF, average mangiferin and isomangiferin enrichments of 20% and 22%, respectively, were obtained. Whilst no correlation was found between the feed concentration of the extracts, xanthone enrichment and fouling index, a strong linear correlation (R2 = 0.98) was found between feed concentration and permeate yield.

AFRIKAANSE OPSOMMING: Cyclopia genistoides (heuningbos) is geidentifiseer as ‘n uitstekende bron vir die produksie van ‘n xantoon-verrykte ekstrak weens sy hoë mangiferien-inhoud sowel as suksesvolle verbouing daarvan. Die oorheersende xantoon teenwoordig in C. genistoides is mangiferien, ‘n kragtige antioksidant met ‘n bewese wye reeks bioaktiwiteite wat grootliks bydra tot die gesondheidsvoordele van heuningbosekstrakte. Isomangiferien, die regio-isomeer van mangiferien met vergelykbare antioksidant-aktiwiteit as mangiferien, is nog ‘n waardevolle verbinding teenwoordig in aansienlike hoeveelhede in C. genistoides. ‘n Xantoon-verrykte ekstrak kan moontlik toegepas word in funksionele voedsel- of drankie-produkte, wat gesondheidsvoordele bo en behalwe die basiese voedsaamheid inhou. Die effek van etanol (EtOH)-konsentrasie (0-100%, v/v), plantmateriaal grootte (gemaal teenoor teesakkie-fraksie), ekstraksietyd (0-60 min) en ekstraksietemperatuur op die ekstraksie van xantone uit ongefermenteerde C. genistoides is ondersoek. Enkelfaktor eksperimente het getoon dat die beste ekstraksie-effektiwiteit, in terme van ekstrakopbrengs, xantoonopbrengs en xantooninhoud van die ekstrak, bereik is deur gemaalde plantmateriaal met 20-60% EtOH (v/v) vir 30 min by verhoogde temperature (70°C) te ekstraheer. Respons-oppervlak Metodologie (ROM) is aangewend om die individuele en interaktiewe effekte van die veranderlikes, naamlik EtOH-konsentrasie (0-100%, v/v) en temperatuur (0-70°C) te ondersoek asook om die ekstraksieproses verder te optimiseer. EtOH-konsentrasie het die grootste effek op die ekstraksie-effektiwiteit gehad (p < 0.05), terwyl die effek van temperatuur onbeduidend was. Optimale vlakke van EtOH-konsentrasie (40% v/v) en temperatuur (70°C) vir maksimum ekstrak- en mangiferienopbrengs is binne die eksperimentele domein is gevind, met die gebruik van 10 mL/g oplosmiddel:vastestof verhouding en ‘n ekstraksietyd van 30 min. Ultrafiltrasie (UF) is daarna gebruik om verdere xantoon-verryking van die ongefermenteerde C. genistoides ekstrak (40% EtOH, v/v) te fasiliteer. ‘n Reeks labratoriumskaal membraantoestelle (sentrifugale membraaneenhede, ‘n geroerde selsisteem en ‘n kruisvloei-ultrafiltrasie (KVU) sisteem) is gebruik in ‘n opskaleringsbenadering om die effek van die membraanmateriaal (geregenereerde sellulose (RS) vs. polyetersulfoon (PES)), molekulêre gewig afsnit (MWCO; 3 kDa, 10 kDa, 30 kDa), voerkonsentrasie (1% vs. 3% oplosbare vastestowwe (OV)) en operasionele parameters (transmembraandruk (TMD) en voervloeispoed) op membraanprestasie en permeaatkwaliteit te bepaal. Die membraan met die beste prestasie in terme van produktiwiteit en xantoon-verryking was die 10 kDa RS membraan wanneer gebruik met ‘n ekstrakkonsentrasie na aan dié van die industrieel vervaardigde ekstrakte (3% OV). ROM is gebruik om die KVU van ongefermenteerde C. genistoides deur ‘n 10 kDa RS membraan verder te optimiseer. Die indiwiduele en interaktiewe effekte van TMD (0.82-2.04 bar) en voervloeispoed (200-444 mL/min) op permeaatvloei, xantoon-verryking en die blokkeringindeks is ondersoek. Die individuele effekte van TMD en voervloeispoed het ‘n betekenisvolle effek op alle gemete response gehad, terwyl hul interaksie net gemiddelde permeaatvloei en besoedelingsindeks beduidend beïnvloed het. Optimale TMD en voervloeispoed waardes van 2.04 bar en 444 mL/min, onderskeidelik, is geselekteer binne die eksperimentele domein, wat bepaal is deur die beperkings van die toerusting. Die geldigheid van die gesamentlike protocol, insluitende etanol-water ekstraksie en UF, is getoets deur plantmateriaal van tien verskillende ongefermenteerde C. genistoides monsters te gebruik. Dit het gelei tot verrykte ekstrakte wat 10.6-17.8% xantone bevat het. UF het onderskeidelik gemiddelde mangiferien- en isomangiferien-verryking van 20% en 22% gelewer. Geen korrelasie is gevind tussen die voerkonsentrasie van die ekstrakte en die besoedelingsindeks nie, maar ‘n goeie liniêre korrelasie (R2 = 0.98) is tussen voerkonsentrasie en permeaatopbrengs gevind.

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