Browsing by Author "Du Preez, Brigitte Von Pressentin"

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    Cyclopia maculata : source of flavanone glycosides as precursors for taste modulating aglycones
    (Stellenbosch : Stellenbosch University, 2014-04) Du Preez, Brigitte Von Pressentin; De Beer, D.; Joubert, E.; Muller, M.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH ABSTRACT: The flavanone aglycones, hesperetin and eriodictyol, have been identified as potential taste modulators with reported sweetness-enhancing and bitterness-masking properties, respectively. Reduction of the sugar content of food products has become important in view of the global obesity epidemic. Taste modulators have shown potential to enhance the sweet taste of reduced-sugar foods without unfavourably affecting their flavour profile. On the other hand, bitterness-masking taste modulators are useful to mask the bitter taste of functional phytochemical ingredients. In the current study, Cyclopia maculata (honeybush) was investigated as potential source of hesperetin- and eriodictyol-enriched extracts. Hesperetin and eriodictyol were present mainly below the quantification limit in C. maculata plant material, including unfermented leaf and stem material, unfermented and fermented tea, as well as the fermented by-product (< 40 mesh and > 12 mesh). Conversely, their rutinoside and modulatinginactive derivatives, hesperidin and eriocitrin were present at substantially higher concentrations in the plant material. The stems and by-product were shown to be good sources of hesperidin, but not eriocitrin. The qualitative and quantitative phenolic profile of the by-product was similar to that of the stems. The tea processing by-product was therefore selected to optimise extraction of flavanone glycosides for subsequent de-glycosylation of the flavanone glycosides to aglycones. The by-product was subjected to ultrasound-assisted extraction to investigate its potential as renewable source of the flavanone glycosides. Response surface methodology (RSM) was employed to optimise and study the individual and interactive effects of the process variables, namely ethanol concentration (% v/v), time (min), temperature (°C), and solvent:solid ratio (mL/g), on flavanone glycoside extraction. The hesperidin yield and content (of extract), as well as extract yield, increased with an increase in extraction time, temperature and solvent:solid ratio. Practical process restrictions limited global optimisation and only an optimum of 52.8% (v/v) ethanol for extract and hesperidin yield could be reached. Temperature was the parameter with the most significant effect (p < 0.05) on extraction efficiency among those studied. Practical process parameter values that were feasible for industrial application (52.8% (v/v) ethanol, 20 mL/g solvent:solid ratio, 60°C and 30 min) were selected for the preparation of a flavanone glycoside-enriched extract from the tea processing by-product. The flavanone glycoside-enriched extract was subjected to acid-catalysed hydrolysis to deglycosylate hesperidin and eriocitrin to hesperetin and eriodictyol, respectively. RSM was employed to optimise the acid hydrolysis process and to study the effect of the hydrolysis parameters (temperature (°C) and time (min)) on hydrolysis efficiency. At the maximum temperature (92.1°C) and corresponding optimum time (98.4 min) ca 80% conversion of hesperidin to hesperetin was achieved. Substantially more eriodictyol formed during acid hydrolysis than eriocitrin present in the initial extract owing to the deglycosylation of unidentified glycosides with the same aglycone. Unidentified breakdown products imparting a red colour to the acid-hydrolysed extract were also observed. The total phenolic content of the acid-hydrolysed extract was significantly higher (p < 0.05) than that of the unhydrolysed extract, indicating the formation of unidentified compounds with the ability to reduce the Folin-Ciocalteau reagent, although no significant difference (p ≥ 0.05) between the antioxidant activities of these extracts, as assessed with the DPPH radical scavenging and ORAC assays, was observed. The potential of enzymatic bioconversion as an alternative to acid-catalysed hydrolysis was investigated using commercial hesperidinase. Bioconversion resulted only in de-rhamnosylation with ca 100% conversion of hesperidin to hesperetin-7-O-glucoside in an aqueous C. maculata extract at pH 4.0 and 40°C.
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    Development of a quality grading system for the honeybush (Cyclopia spp.) tea industry
    (Stellenbosch : Stellenbosch University, 2020-12) Du Preez, Brigitte Von Pressentin; Joubert, Elizabeth; Muller, Magdalena; Moelich, Erika Ilette; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Honeybush tea, produced from Cyclopia species endemic to South Africa, has attained an international footprint within the global herbal tea sector. As demand is exceeding supply to a primarily export market, all production batches should meet optimum quality standards. The lack of standardised sensory quality criteria and assessment methods within the commercial sector has resulted in tea of variable sensory quality reaching the market. The trade of inconsistent and inferior quality products will be detrimental to the reputation of honeybush tea and consumer acceptance, and ultimately the honeybush industry. The need for a scientifically founded quality grading system to evaluate, differentiate and communicate the sensory quality of honeybush tea was addressed through four quality control elements, i.e. a sensory lexicon and wheel, sensory quality standard, quality scoring method, and rapid quality classification methods. The previously developed honeybush aroma lexicon and wheel were revised, based on a newly established comprehensive sensory and physicochemical dataset. Data of samples of the main commercial Cyclopia species (C. intermedia, C. subternata and C. genistoides), processed on laboratory- and commercial-scale, were incorporated to represent the sensory space in terms of different qualities. Universal chemical-based reference standards were developed and validated to replace food-based reference standards in the aroma lexicon to facilitate standardised assessment of honeybush sensory quality. The established sensory quality standard was founded on the comprehensive dataset and input from industry. Sensory quality parameters for the tea infusions and dried plant material were identified, and parameter specifications for ‘high’, ‘moderate’, ‘low’ and ‘poor’ quality classes were defined through expert focus groups. A user-friendly quality scoring method that incorporates a scorecard and colour reference card, was developed and validated for the assessment and classification of production batches based on obtained parameter and total score values and citation frequencies of specific attributes. The validity of reference-based rapid methods, polarised sensory positioning (PSP) and polarised projective mapping (PPM), were investigated for their discrimination ability as time-efficient classification tools to distinguish between infusions of large samples sets of variable sensory quality within commercial and research context. The efficacy of the use of physical (p) poles (tea infusions) and novel theoretical (t) poles (descriptions), representative of the four sensory quality classes, as references, were compared within each method, using a trained panel. Product configurations similar to that of a classical sensory profiling method, descriptive sensory analysis, demonstrated the validity of the method variations for broad quality classification based on key sensory quality parameters. PPM-p indicated the highest discrimination ability between the quality classes. Recommended amendments to theoretical pole descriptions would improve feasibility for commercial application. The quality scoring method and PPM-t were tested by a panel of industry representatives, and the need for industry assessor training in sensory quality parameters was emphasised. Implementation of the proposed integrated quality grading system will equip honeybush industry role-players in delivering a final product of consistent sensory quality within the honeybush value chain.
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    Development of chemical-based reference standards for rooibos and honeybush aroma lexicons
    (Elsevier, 2019) Du Preez, Brigitte Von Pressentin ; De Beer, D.; Moelich, E. I.; Muller, M.; Joubert, E.
    The honeybush sensory wheel was revised, using a large sample set (n = 585) comprising of the major commercial Cyclopia species, i.e. C. intermedia, C. subternata and C. genistoides. Only positive and negative aroma attributes were included in the wheel. Chemicals were identified to serve as reference standards for the honeybush (Cyclopia spp.) lexicon. Similarly, chemical-based reference standards were identified for the rooibos (Aspalathus linearis) lexicon. From a comprehensive literature search and gas chromatography–mass spectrometry analyses, chemicals were screened by an expert panel for their suitability in terms of typicality of the target aroma. Each chemical was evaluated in a ‘base tea’ and compared to a specific ‘reference tea’ exhibiting a high intensity of the target aroma. A total of 30 and 44 chemicals for rooibos and honeybush, respectively, were selected for validation by a trained panel. Descriptive sensory analysis was conducted to assign typicality and intensity scores for each chemical representing a target aroma attribute. Several chemicals were identified as suitable reference standards for the following aroma notes: isophorone (‘rooibos-woody’), maltyl isobutyrate (‘caramel’), cis-3-hexenol (‘green grass’), 4-oxoisophorone (‘seaweed’) and 2,4,6-trichloroanisole (‘musty/mouldy’) for rooibos; and 2-acetyl-5-methylfuran (‘woody’), levulinic acid (‘fynbos-sweet’), maltyl isobutyrate (‘caramel’), and 2-acetylpyrrole (‘nutty’) for honeybush.