Grape marc is an underutilised bio-waste comprising predominantly grape skin and seeds. It is produced as a waste product of winemaking on the million-tonne scale annually. The most important high-value current use of grape marc is in the production of oenological tannins - widely-used additives in the food and beverage industry. More commonly, grape marc is simply either disposed of, or used as feed or fertiliser. With recent evidence showing that grape extracts enriched in grape tannins contain significant amounts of the thiol precursors 3-S-cysteinylhexan-1-ol and 3-S-glutathionylhexan-1-ol, and the possibility that these could influence food and beverage aroma, an investigation of grape marc extraction procedures was undertaken, in order to try to define extraction protocols that could maximise the recovery of these compounds. Sixty six different solvent combinations were explored using solid-liquid extractions on Sauvignon Blanc grape marc, utilizing only environmentally benign solvents. Effective extraction of commercially relevant thiol precursors was successfully achieved, and is the first identification of thiol precursors in grape marc. Additionally, extraction was achieved in mixtures high in water content, which is an economic and environmental advantage and adds a significant potential commercial value to this underutilised waste product. Numerous bioactive phenolics were also obtained using these developed methods and have subsequently been used for the preparation of novel bioactive materials.

Extraction and utilisation of bioactive monomeric phenolics and commercially valuable flavour precursors from grape waste

256th National Meeting (2018)

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