Browsing by Author "Pauck, Claire Elizabeth"

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    Effects of formulation on the stability of green Cyclopia subternata extract during spray-drying and storage
    (Stellenbosch : Stellenbosch University, 2016-03) Pauck, Claire Elizabeth; Joubert, Elizabeth; De Beer, Dalene; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.
    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.