Browsing by Author "Herbst, Jacqueline"

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    Aqueous two-phase systems for the extraction of polyphenols from wine solid waste
    (Stellenbosch : Stellenbosch University, 2019-12) Herbst, Jacqueline; Pott, Robert William M.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: The South African wine industry produces large amounts of solid waste, which is left over after the wine making process is complete. This solid waste accounts for approximately 25% of the fresh grape mass used for wine making and is called pomace. The pomace includes the parts of the grape not converted to wine: the skins, seeds and stems. These contain valuable compounds which could be used, for instance, for nutraceuticals, thus allowing for the valorisation of the wine solid waste. Included in these compounds are polyphenols. Polyphenols are compounds containing aromatic rings with hydroxyl groups, many of which have interesting or useful properties, such as being strong antioxidant molecules, and are therefore sought after for therapeutics and cosmetics. Polyphenols have been extracted from various plant sources using conventional extraction methods, such as solvent extraction using either methanol or ethanol or supercritical CO2 extraction. These solvents or processes are often expensive, and the high volumes needed drives up the processing costs. Alternative methods are needed to provide more cost-effective extraction processes, while also a Green Chemistry approach to extraction by taking into consideration the environmental impacts of the process and reducing harmful solvent use. One such alternative extraction is the use of Aqueous Two-Phase Systems (ATPS), which have been used as a process alternative for biomolecule extractions, including polyphenols. ATPS are composed of two immiscible aqueous solutions, often created with polyethylene glycol (PEG) and salt. Two phases form when these components are within specific concentration bounds. The biomolecules are extracted from the plant material using the ATPS and then concentrated to one phase of the ATPS. Many different PEG and salt combinations exist and have been studied in the literature, looking at the phase behaviour as well as the ability of the ATPS to extract and concentrate the biomolecules. In this study, ATPS with PEG 6000, PEG 8000 and PEG 10 000 with potassium sodium tartrate were studied. In the first set of experimentation, the phase behaviours were looked at, at different temperatures by constructing phase diagrams which included binodal curves and tie-line information (which define the two-phase region). The binodal data were fitted with a non-linear model, called the Merchuck equation, and the tie-line data were validated using the Othmer-Tobias and Bancroft equations. Phase diagrams were constructed to visualise these effects and indicated that higher temperatures and larger PEG molecular weights favoured phase formation, producing ATPS with a wider range of PEG/salt compositions. These results have been published in The Journal of Chemical and Engineering Data. In the next set of experimentation, these ATPS were evaluated for their ability to extract and concentrate polyphenols from wine solid waste, compared to a solvent extraction using ethanol/water (80:20 v/v). Various parameters were investigated including PEG Mw, salt type, TLL, extraction temperature, extraction time, pH, biomass loading and phase separation temperature. It was found that temperature, PEG composition (TLL) and biomass loading were the biggest drivers in improving the extraction and concentrating ability of the ATPS. The ATPS ability was judged using yield and partitioning coefficient (K) of the polyphenols by gallic acid equivalents (GAE). Yields upwards of 85% were achieved, with the K varying between 2-4, the highest K of 7.2 achieved by only one ATPS, which had the biggest fraction of PEG in the total ATPS composition. The results show that ATPS can be successfully used as an extraction method for polyphenols from wine solid waste.