Effects of formulation on the stability of green Cyclopia subternata extract during spray-drying and storage

Pauck, Claire Elizabeth (2016-03)

Thesis (MSc Food Sc)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: Green Cyclopia subternata (honeybush) hot water extracts (GCSE) have potential as value-added functional food ingredients based on their anti-obesity and anti-diabetic properties. They are thus suitable for inclusion in reduced-kilojoule instant iced tea powder formulations. The aims of this study were to determine the effect of spray-drying, with and without carriers, on the stability of GCSE and the effect of product formulation and storage at different conditions on iced tea powder mixtures containing GCSE. GCSE was spray-dried without (control) and with added carriers, i.e. corn syrup solids (CS) and inulin (IN) at four treatment levels (0, 25, 50 and 75%). IN was selected for the final iced tea powder formulation due to its prebiotic properties, but solubility limited practical inclusion of IN in iced tea powder to levels of 25% (IN25). Six formulations (T1 = spray-dried GCSE; T2 = IN25; T3 = IN25 + sugar; T4 = IN25 + xylitol + stevia; T5 = T3 + citric acid + ascorbic acid; T6 = T4 + citric acid + ascorbic acid) were subjected to a six month shelf-life stability trial at ambient (25 °C/55% relative humidity (RH)) and accelerated (40 °C/75% RH) conditions. Physicochemical properties of the spray-dried and iced tea powders were characterised in terms of phenolic retention, moisture content (MC), water activity (aw), moisture sorption isotherms (MSI) and objective colour measurements. Isothermal microcalorimetry (IMC) was used to determine if the ingredients of mixtures interacted with one another and to assess the effect of raised RH conditions (25°C/55% RH and 40°C/75% RH) on the stability of the iced tea powders. Differential thermal analysis (DTA) was applied to measure the phase transition temperatures of the powders, X-ray powder diffraction (XRPD) measurements confirmed the crystalline or amorphous nature of the powders, and contact angle measurements indicated wettability of the powder. Spray-drying produced fine, light brown, amorphous and free-flowing powders. The MC and aw of the powders fell within the range of the monolayer moisture values calculated using the BET model from MSI data. IN and CS produced powders with similar characteristics and were compatible with GCSE, with the exception of mixtures containing 75% CS. Heating conditions during spray-drying had a negligible effect on the bioactive phenolic content and the free radical scavenging capacity of the extract. Therefore spray-drying was considered to be a suitable method of producing dried honeybush extracts. XRPD and DTA showed no significant phase transition for the iced tea powders during storage. IMC detected no incompatibilities between ingredients in the mixtures. Physicochemical characteristics of the powders remained stable and adequate phenolic retention was achieved at ambient temperature (25 °C). However, when the powders were stored at 40 °C, the presence of the acids caused drastic degradation of phenolic compounds and physicochemical changes resulting in prominent colour changes. IMC at 55% RH showed that amorphous powders (spray-dried extract and stevia) deliquesced. At 75% RH mixtures containing xylitol underwent deliquescence, while those with sugar remained stable. An iced tea powder containing GCSE should therefore be stored at ambient temperature in moisture impermeable packaging to ensure adequate stability.

AFRIKAANSE OPSOMMING: Groen Cyclopia subternata warm water ekstrakte (GCSE) het potensiaal as waarde-toegevoegde funksionele voedsel bestandele gebaseer op hul anti-vetsug en anti-diabetiese eienskappe. Sulke ekstrakte is dus geskik om in ‘n verminderde-kilojoule kits-ystee poeier formulasie gebruik te word. Die doelstellings van hierdie studie was om die effek van sproeidroging, met en sonder draers, op die stabiliteit van GCSE te bepaal, asook die effek van produk formulasie en opberging by verskillende toestande op ystee-mengsels wat GCSE bevat te bestudeer. GCSE is gesproeidroog sonder (kontrole) en met draers, d.i. mieliestroop-vastestowwe (MS) en inulin (IN) teen vier behandelingsvlakke (0, 25, 50 en 75%). IN is gekies vir die finale poeier ystee formulasie weens sy pre-biotiese eienskappe maar oplosbaarheid het die byvoeging van IN in ystee-poeier beperk tot 25% (IN25). Ses formulasies (T1 = gesproeidroogde GCSE; T2 = IN25; T3 = IN25 + suiker; T4 = IN25 + xylitol + stevia; T5 = T3 + sitroensuur + askorbiensuur; T6 = T4 + sitroensuur + askorbiensuur) is onderwerp aan ‘n ses maande rakleeftyd studie by normale (25 °C/55% relatiewe humiditeit (RH)) en versnelde (40 °C/75%RH) opbergings toestande. Die fisies-chemiese eienskappe van die gesproeidroogde en ystee-poeiers is gekarakteriseer in terme van fenoliese behoud, voginhoud (VI), water aktiwiteit (aw), vog-sorpsie-isoterme (VSI) en objektiewe kleur metings. Isotermiese mikrokalorimetrie (IMK) is gebruik om te bereken of daar interaksie is tussen die bestandele van die mengsels, en om die uitwerking van opberging RH toestande (25 °C/55% RH en 40 °C/75% RH) op die stabiliteit van ystee-poeiers te bepaal. Differensiële termiese analiese (DTA) is gebruik om die fase oorgangs temperature van die poeiers te bepaal, X-straal poeier diffraksie (XRPD) meetings het die kristal- of amorfe-karaktereienskappe van die poeiers bevestig, en kontak-hoek metings het die benatingspotesiaal van die poeier aangedui. Sproeidroging het fyn, ligte-bruin, amorfe en vry-bewegende poeiers geproduseer. Die VI en aw van die poeiers was in die omvang van die monolaag voginhoud waardes, soos bereken met die BET model van die VSI data. IN en MS het poeiers met soortgelyke eienskappe opgelewer en het nie interaksie met GCSE getoon nie, behalwe in geval van mengsels met 75% MS. Die verhittingskondisies gedurende sproeidroging het ‘n minimale effek op die bioaktiewe phenoliese-inhoud en die vryradikaal blussings vermoë van die ektrak gehad. Daarom is sproeidroging aanvaar as ‘n effektiewe manier om gedroogde heuningbostee ekstrakte te vervaardig. XRPD en DTA het geen verskille in die fase oorgangs van ystee-poeiers gedurende opberging getoon nie, terwyl IMK het geen interaksie tussen bestandele van die mengsels getoon het nie. Die Stellenbosch University https://scholar.sun.ac.za v fisies-chemiese eienskappe van poeiers was stabiel en aanvaarbaare behoud van fenoliese verbindings is behaal by kamertemperatuur (25 °C). Opberging by 40 °C het egter getoon dat die sure drastiese afbreking van die fenoliese verbindings asook fisies-chemiese veranderinge veroorsaak. Die fisies-chemieses veranderings het kleur veranderings veroorsaak. IMK teen 55% RH het bewys dat amorfepoeiers (gesproei-droogde ekstrak en stevia) het vloiebaar geword. By 75% RH het die mengsels met xylitol ook vloeibaar geword, terwyl die met suiker stabiel gebly het. ‘n Ystee-poeier met GCSE moet dus by kamertemperatuur en in vog-ondeurlaatbare verpakking opgeberg word om stabiel te bly.

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