The physicochemical properties and stability of aspalathin in micro- and nanoencapsulated green rooibos extract formulations

Human, Chantelle (2019-04)

Thesis (PhD(FoodSc)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Green rooibos extracts with high aspalathin content have potential as nutraceutical food ingredients based on their properties relating to the prevention of metabolic syndrome. However, delivery of green rooibos extracts in convenient beverage products is a challenge due to poor stability of aspalathin in the presence of moisture. Thus, the development of alternative ingredients and convenience products is required. Microencapsulation of a green rooibos extract (GRE) with maltodextrin as control carrier and inulin and chitosan as low kilojoule functional alternatives was achieved by spray-drying. Spray-dried GRE and powders containing maltodextrin or inulin had similar yields (>76%), moisture content (<3.5%) and aspalathin retention (>95%), whereas microencapsulation with chitosan resulted in lower yields (<66%), higher moisture content (>3.4%) and lower aspalathin retention (<83%). Accelerated stability tests (40 °C/75% relative humidity (RH)) revealed similar aspalathin degradation rates (based on fractional conversion model) for GRE, inulin and maltodextrin formulations, but significantly higher degradation rates for chitosan formulations. Given the low incompatibility between GRE and inulin, inulin-microencapsulated GRE (1:1 ratio; IN50) was selected as the most suitable green rooibos nutraceutical beverage ingredient. IN50 was added to iced tea powder formulations, which contained various food grade ingredients (sucrose, xylitol, citric acid and ascorbic acid). Shelf-life trials (30 °C and 40 °C/65% RH for 5–12 months) in different packaging materials (semi-permeable vs impermeable) revealed more aspalathin degradation (based on first order reaction rates), more discolouration and clumping after the addition of crystalline ingredients. These changes were more pronounced at 40 °C and for powders stored in the semi-permeable packaging. The formulation containing IN50, xylitol and citric acid, which showed the most drastic physical and chemical changes during storage, was subjected to descriptive sensory analysis, which confirmed significant changes also in its sensory profile. Nanoencapsulation of an aspalathin-rich fraction (GRAF) prepared from green rooibos was also investigated. Combinations of natural (chitosan and lecithin) and synthetic [poly(lactide-co-glycolide) and Eudragit S100® (ES100)] polymers with suitable conventional methods and electrospraying were investigated. Overall, ES100 electrosprayed particles had the best combination of properties, i.e. encapsulation efficiency (EE, 55.4%), loading capacity (LC, 11.1%), release rate at pH 7.4 (1.67 h-1) and size (190 nm). Further optimisation of the ES100-GRAF loaded nanoparticles was achieved using a central composite design. Responses included yields between 78.2–78.3%, EE between 73.9–76.4% and LC between 9.9–12.9%. Pure aspalathin was subsequently encapsulated using the optimal conditions, resulting in a similar yield, EE, LC, particle size and particle morphology to that of GRAF loaded nanoparticles. The stability of the aspalathin and GRAF loaded nanoparticles was investigated at fixed pH-time combinations. Nanoencapsulation offered a more stable environment for aspalathin. Overall, pure aspalathin was less stable than when in GRAF. Even though intestinal permeability could theoretically be improved with nanoencapsulation, the parallel artificial membrane permeability assay and Caco-2 cell model indicated that pure aspalathin and aspalathin nanoparticles both have equally low permeability. These methods offered an alternative for the production of GRE convenience products and ingredients, whilst providing insight on the effects of encapsulation and ingredients of powder formulations.

AFRIKAANSE OPSOMMING: Groen rooibos ekstrakte met hoë aspalatien inhoud het potentiaal as nutraseutiese voedsel bestandele, gebaseer op eienskappe wat verband hou met voorkoming van die metaboliese sindroom. Die lewering van groen rooibos ekstrakte in gerieflike ys-tee vorm is egter ‘n uitdaging, as gevolg van die lae stabiliteit van aspalatien in die teenwoordigheid van vog. Dus, word die ontwikkeling van alternatiewe bestandele en gerieflikheids produkte benodig. Mikro-enkapsulering van ‘n groen rooibos ekstrak (GRE) met maltodekstrien as kontrole polimeer en inulien en chitosan as lae kilojoule funksionele alternatiewe is behaal met sproeidroging. Gesproei-droogte GRE en poeiers wat maltodekstrien en inulien bevat het soortgelyke opbrengs (>76%), vog inhoud (<3.5%) en aspalatien retensie (>95%) gehad, terwyl mikro-enkapsulering met chitosan laer opbrengs (<66%), hoër vog inhoud (>3.4%) en laer aspalatien retensie (<83%) gehad het. Versnelde stabiliteits toetse (40 °C/75% relatiewe humiditeit (RH)) het soorgelyke aspalatien degradasie tempo’s (gebaseer op die fraksionele omskakelingsmodel) vir GRE, inulien en maltodekstrien formulasies onthul, maar betekenisvolle hoër degradasie tempo’s vir chitosan formulasies. Aangesien geen interaksies tussen GRE en inulien getoon is nie, is inulien-gemikro-enkapsuleerde GRE (1:1 verhouding, IN50) gekies as mees geskik vir ‘n gepoeierde groen rooibos nutraseutiese bestandeel. IN50 is in ys-tee poeier formulasies gevoeg wat verskeie voedselgraad bestanddele bevat het (sukrose, xylitol, sitroensuur en askorbiensuur). Rakleeftyd proewe (30 °C en 40 °C/65% RH vir 5–12 maande) in verskillende verpakkingsmateriale (semi-deurlaatbaar vs ondeurlaatbaar) het meer aspalatien afbraak (gebaseer op eerste orde reaksie tempo’s), meer verkleuring en klontvorming is onthul na byvoeging van kristallyne bestanddele. Die veranderinge was meer prominent by 40 °C en vir poeiers opgeberg in semi-deurlaatbare verpakking. Die formulasie wat IN50, xylitol en sitroensuur bevat en die mees drastiese fisiese en chemiese veranderinge getoon het tydens opberging, is onderwerp aan beskrywende sensoriese analise, wat betekenisvolle veranderinge in die sensoriese profiel bevestig het. Nano-enkapsulering van ‘n aspalatien-ryke fraksie (GRAF) voorberei van groen rooibos is ook ondersoek. Kombinasies van natuurlike (chitosan en lesitien) en sintetiese [poli(laktied-ko-glikolied) en Eudgragit S100® (ES100)] polimere met gepaste konvensionele metodes en die elektrosproei tegniek is ondersoek. Algeheel het die ES100 ge-elektrosproeide partikels die beste kombinasie van resultate getoon in terme van enkapsuleeringsdoeltreffenheid (ED, 55.4%), laaikapasiteit (LK, 12.7%), aspalatien vrylatings tempo by pH 7.4 (1.67 h-1) en grootte (190 nm). Verdere optimisering van die ES100-GRAF gelaaide nanopartikels is behaal met ‘n sentrale saamgestelde ontwerp. Die uitkomstes het ingesluit opbrengs tussen 78.2–78.3%, ED tussen 73.9–77.4% en LK tussen 10.4–12.2%. Suiwer aspalatien was daaropvolgend ge-enkapsuleer onder die ge-optimiseerde kondisies en soortgelyke opbrengs, ED, LK, partikel grootte en partikel argitektuur as die GRAF gelaaide partikels is gevind. Die stabiliteit van die aspalatien en GRAF gelaaide nanopartikels is ondersoek by vaste pH-tyd kombinasies. Nano-enkapsulering het ‘n meer stabiele omgewing vir aspalatien gebied. Algeheel was suiwer aspalatien minder stabiel as in GRAF. Alhoewel dermwand deurdringbaarheid teoreties verbeter kon word met nano-enkapsulering, het die parallel kunsmatige membraan deurdringbaarheidstoets en die Caco-2 sel model getoon dat suiwer aspalatien en aspalatien nanopartikels albei ewe lae deurdringbaarheid het. Hierdie metodes bied alternatiewe vir die produksie van groen rooibos gerieflikheidsprodukte en bestanddele terwyl insig gegee word op die effekte van enkapsulering en bestanddele van poeier formulasies.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105721
This item appears in the following collections: