Aqueous two-phase systems for the extraction of polyphenols from wine solid waste

Herbst, Jacqueline (2019-12)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

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.

AFRIKAANSE OPSOMMING: Die Suid-Afrikaanse wynindustrie produseer groot hoeveelhede vastestofafval, wat oorbly nadat die wynmaakproses voltooi is. Hierdie vastestofafval geld vir omtrent 25% van die vars druiwe massa wat gebruik word om wyn te maak, en word pulp genoem. Die pulp sluit die dele van die druif in wat nie na wyn omgeskakel kan word nie: die dop, saad en stingels. Hierdie bevat waardevolle samestellings wat gebruik kan word vir byvoorbeeld neutraseutiese middels, en dus die valorisasie van die wynvastestofafval toelaat. Hierdie samestellings bevat polifenole. Polifenole is samestellings wat aromatiese ringe bevat met hidroksielgroepe, waarvan daar baie met interessante en bruikbare eienskappe is, soos om sterk anti-oksidant molekules te wees, en word daarom vir terapeutiese en kosmetiese doeleindes gesog. Polifenole is deur verskeie plantbronne geëkstraheer deur konvensionele ekstraksiemetodes te gebruik, soos ʼn oplosmiddelekstraksie wat of metanol-, etanol- of superkritiese CO2-ekstraksie gebruik. Hierdie oplosmiddels of prosesse is gereeld duur, en die hoë volumes wat benodig word, stoot die prosesseringkostes op. Alternatiewe metodes word dus benodig om meer koste-effektiewe ekstraksieprosesse te verskaf, terwyl ʼn Groen Chemie-benadering op ekstraksie terselfdertyd geneem moet word deur ook die omgewingsimpak van die proses in ag te neem en die skadelike oplosmiddels wat gebruik word, te verminder. Een so ʼn alternatiewe ekstraksie is die gebruik van Waterige Twee-fase Sisteme (ATPS), wat gebruik is as ʼn alternatiewe proses vir biomolekulêre ekstrakies, insluitend polifenole. ATPS word deur twee onmengbare waterige oplossings saamgestel, dikwels uit poliëtileenglikol (PEG) en sout geskep. Twee fases vorm wanneer hierdie komponente binne spesifieke konsentrasies bind. Die biomolekules word geëkstraheer vanuit die plantmateriaal deur die ATPS te gebruik, en dan gekonsentreer na een fase van die ATPS. Baie verskillende PEG en sout kombinasies bestaan en is bestudeer in die literatuur, waar gekyk word na die fase gedrag sowel as die vermoë van die ATPS om die biomolekules te ekstraheer en konsentreer. In hierdie studie, is ATPS met PEG 6000, PEG 8000 en PEG 10 000 met kaliumnatriumtartraat bestudeer. In die eerste stel eksperimente, is daar na die fase gedrag gekyk, by verskillende temperature deur fase diagramme te konstrueer wat binodale kurwes en bindlyninformasie (wat die twee-fase streek definieer), bevat. Die binodale data is gepas met ʼn nie-liniêre model, wat die Merchuck-vergelyking genoem word, en die bindlyndata is gevalideer deur die Othmer-Tobias en Bancroft vergelykings. Fase diagramme is konstrueer om hierdie effekte te visualiseer en het aangedui dat hoër temperature en groter PEG-molekulêre massas die fase formasie bevoordeel, wat ATPS met ʼn wyer bestek PEG/sout-samestellings produseer. Hierdie resultate is in The Journal of Chemical Engineering Data gepubliseer. In die volgende stel eksperimente is hierdie ATPS geëvalueer vir hulle vermoë om polifenole uit wynvastestofafval te ekstraheer en konsentreer, in vergelyking met ʼn oplosmiddelekstraksie wat etanol/water (80:20 v/v) gebruik. Verskillende parameters is ondersoek, insluitend PEG Mw sout tipe, TLL, ekstraksietemperatuur, ekstraksietyd, pH, biomassa-lading en fase verdeling-temperatuur. Dis gevind dat temperatuur, PEG-samestelling (TLL) en biomassa-lading die grootste drywers was om die ekstraksie- en konsentrasievermoë van die ATPS te verbeter. Die ATPS-vermoë is beoordeel deur opbrengs en verdelingskoëffisiënt (K) van die polifenole by gallussuurekwivalente (GAE) te gebruik. Opbrengs opwaarts van 85% is bereik, met die K wat tussen 2 en 4 varieer, die hoogste K van 7.2 is deur slegs een ATPS bereik, wat die grootste fraksie van PEG in die totale samestelling gehad het. Die resultate wys dat ATPS suksesvol gebruik kan word as ʼn ekstraksiemetode vir polifenole uit wynvastestofafval.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107209
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