Bioprocessing of grape pomace

[摘要] ENGLISH SUMMARY: Grape pomace is the primary by-product that is generated during grape juice processing andwine production. It consists of fibrous materials that include the processed skins, stems andseeds. Beneficial in many ways, it can be used as compost, animal feed, food fibre, or asource of tartrates and citric acid. Stricter environmental regulations, however, necessitatedefforts to rethink methods of recycling pomace into useful products to reduce the removaland operating costs. Due to the potential use of bio-ethanol, this study was aimed atevaluating the potential recovery of ethanol from grape pomace. We therefore investigatedthe potential of microbial hydrolysis and fermentation of grape pomace to explore theeconomic benefits of bioprocessing.Naturally occurring microorganisms associated with pomace were isolated and their abilityto degrade pure polysaccharides was evaluated. The results indicated nine yeast, eightbacterial, one actinomycete and three fungal species displaying varying levels and types ofenzyme activity for the hydrolysis of polysaccharides. Only positive yeast isolates werefurther identified as they are known for their ability to ferment sugars to alcohol. Sincegrape pomace consists of the four major polysaccharides in nature, i.e. cellulose,hemicellulose, pectin and starch, proper hydrolysis thereof could make themonosaccharides available to microorganisms for alcoholic fermentation. The extent ofhydrolysis, types of degradation products and ethanol production were determined.The yeast Pichia rhodanensis, when compared to two recombinant strains ofSaccharomyces cerevisiae containing several genes for saccharolytic enzymes, showedparticularly promising results with the absorbency assays. However, this assay method didnot 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 thanby the sugars released and the ethanol produced, are required. The economic viability ofhydrolysing pomace with P. rhodanensis and the industrial application thereof should befurther evaluated and optimised. If a cost-effective biodegradation process can be developed, it could then be applied to other agricultural by-products and contribute toethanol production for commercial interest.

[发布机构] Stellenbosch University