Bioprocessing of grape pomace


Thesis (M.Sc.) -- University of Stellenbosch, 1999.ENGLISH SUMMARY: Grape pomace is the primary by-product that is generated during grape juice processing and wine production. It consists of fibrous materials that include the processed skins, stems and seeds. Beneficial in many ways, it can be used as compost, animal feed, food fibre, or a source of tartrates and citric acid. Stricter environmental regulations, however, necessitated efforts to rethink methods of recycling pomace into useful products to reduce the removal and operating costs. Due to the potential use of bio-ethanol, this study was aimed at evaluating the potential recovery of ethanol from grape pomace. We therefore investigated the potential of microbial hydrolysis and fermentation of grape pomace to explore the economic benefits of bioprocessing. Naturally occurring microorganisms associated with pomace were isolated and their ability to degrade pure polysaccharides was evaluated. The results indicated nine yeast, eight bacterial, one actinomycete and three fungal species displaying varying levels and types of enzyme activity for the hydrolysis of polysaccharides. Only positive yeast isolates were further identified as they are known for their ability to ferment sugars to alcohol. Since grape pomace consists of the four major polysaccharides in nature, i.e. cellulose, hemicellulose, pectin and starch, proper hydrolysis thereof could make the monosaccharides available to microorganisms for alcoholic fermentation. The extent of hydrolysis, types of degradation products and ethanol production were determined. The yeast Pichia rhodanensis, when compared to two recombinant strains of Saccharomyces cerevisiae containing several genes for saccharolytic enzymes, showed particularly promising results with the absorbency assays. However, this assay method did not provide any information on the specific enzyme activities or the type of sugars released. Methods to determine an organisms' ability to degrade pomace polysaccharides other than by the sugars released and the ethanol produced, are required. The economic viability of hydrolysing pomace with P. rhodanensis and the industrial application thereof should be further evaluated and optimised. If a cost-effective biodegradation process can be developed, it could then be applied to other agricultural by-products and contribute to ethanol production for commercial interest.AFRIKAANSE OPSOMMING: Stingels, sade en doppe is die primere afvalprodukte wat gedurende die prosessering van druiwesap en wyn gegenereer word. Hierdie veselagtige materiaal word gunstig as kompos, dierevoeding, vesel, of as 'n bron van sitroensuur en wynsteensuur aangewend. Druiwe-afval veroorsaak egter omgewingsbesoedeling en strenger maatreels noodsaak altematiewe metodes om dit in bruikbare produkte te omskep om sodoende die verwydering en bestuurskoste te verminder. Die potensiele gebruik van bio-ethanol noodsaak hierdie studie om druiwe-afval vir die herwinning van etanol te evalueer. Die mikrobiese hidrolise en fermentasie van druiwe-afval is dus ondersoek om die ekonomiese voordele van bio-prosessering te ondersoek. Die mikroorganismes wat natuurlik met druiwe-afval geassosieerd is, is geisoleer en hul vermoe om suiwer polisakkariede te hidroliseer is evalueer. Resultate het nege gis, agt bakteriee, een aktinomiseet en drie fungi spesies aangedui met uiteenlopende ensiem tipes en aktiwiteite vir die hidrolise van polisakkariede. Slegs die positiewe gis-isolate is verder geidentifiseer, aangesien giste bekend is vir hul vermoe om suikers na alkohol te fermenteer. Druiwe-afval bestaan uit die vier vemaamde polisakkariede in die natuur, naamlik sellulose, hemisellulose, pektien en stysel. Die volledige hidrolise van hierdie polisakkaride kan die monosakkariede aan mikroorganismes beskikbaar stel vir moontlike alkoholiese fermentasie. Die mate van hidrolise, die soort afbraakprodukte en die etanol produksie is bepaal. Die gis Pichia rhodanensis het belowende resultate met die absorbansie toetse getoon, in vergelyking met die rekombinante rasse van Saccharomyces cerevisiae wat verskeie ensiemgene vir polisakkaried hidrolise bevat. Hierdie toets het egter geen inligting oor die spesifieke ensiem aktiwiteite of tipe suikers wat vrygestel is, voorsien nie. Metodes om 'n organismes se vermoe om polisakkariede in druiwe-afval te hidroliseer buiten die vrygestelde suikers en etanol produksie word benodig. Die ekonomiese prosessering van die druiwe-afval met P. rhodanensis en die industriele toepassing moet verder evalueer en optimiseer word. Indien 'n koste-effektiewe biologiese proseseringsproses ontwikkel kan word kan dit ook op ander landbou afvalprodukte toegepas word en tot die produksie van etanol vir kommersiele gebruik bydra.Maste

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