The extraction of resveratrol and other polyphenols from solid winery waste and an investigation into alternative resveratrol recovery techniques
Thesis (MEng)--Stellenbosch University, 2020.
ENGLISH ABSTRACT: Resveratrol is a phenolic compound that is produced by several plant species such as grape (Vitis vinifera) as a protection mechanism against both biotic and abiotic stress. Resveratrol is currently of interest and under investigation as nutraceutical supplement, and there is a significant market value for the compound. Winemaking is one of the largest agricultural activities in the world and produces significant amount of solid biomass waste, which is often rich in resveratrol. The aim of this work was to investigate, through consecutive harvests to estimate variability, solid winery waste as a source of resveratrol to produce a high value antioxidant supplement. As well as to investigate aqueous two-phase systems and protein precipitation as resveratrol recovery methods and improve downstream purification processes. In order to extract and recover the maximum amount of resveratrol, sample preparation and process conditions that could result in degradation were investigated. No resveratrol degradation was observed during biomass storage, drying and extraction. However, it was found that resveratrol is sensitive to changes in pH and will degrade under basic conditions. In this study the different parts of solid winery waste from a 2018 and 2019 harvest was investigated as possible resveratrol sources. From the comparison of the different sources over time it was found that the 2019 Pinotage stems contained a maximum of 73 ± 4.3 μg/g resveratrol. Maltodextrin (dextrose equivalence 16.5-19.5) and polyethylene glycol (PEG) 8000 aqueous two-phase systems (ATPS) were investigated to partition and concentrate extracted resveratrol into edible maltodextrin. It was found that for all the systems investigated most of the resveratrol remained in the PEG phase, indicating no concentrating effect to the desired phase. The use of proteins to recover resveratrol by forming a precipitate was investigated by determining the amount of resveratrol precipitated with ovalbumin, tryptone soy broth and yeast extract. For the systems investigated a maximum of 83 ± 2.1% resveratrol formed a recoverable precipitate with yeast extract, indicating a viable recovery method. From the of resveratrol degradation, it was concluded that the process conditions investigated can be used to quantify resveratrol in solid winery waste. Significantly variable resveratrol concentrations were noted between consecutive harvests, indicating a high variability in productivity. Further, resveratrol distribution throughout the plant was highly variable with negligible resveratrol extracted from the grape skins, seeds and leaves and up to 73 ± 4.3 μg/g resveratrol extracted from the canes. Nonetheless, it was concluded that Pinotage solid winery waste can be used as a possible source of resveratrol. By evaluating protein precipitation as a resveratrol method, it was concluded that the selected proteins interacted with resveratrol to form a recoverable precipitate and could be used as a resveratrol recovery method. By comparing the recovery achieved with ATPS to protein precipitation, it was concluded that the amount of resveratrol recovered is too low with maltodextrin-PEG ATPS to be used as a feasible recovery method.