Partial (one month) composting of solid olive processing waste is shown to produce extractable emulsifiers. Size exclusion chromatography (SEC) and Fourier-transform infra-red spectroscopy (FTIR) show that these consist of polysaccharides and proteins from the composted waste. Aqueous extraction at pH 5, pH 7, and pH 9 all yield extracts rich in oligosacchrides and oligopeptides which derive from the break-down of the macromolecules under composting, with the extract obtained at pH 5 being the richer in such components. Fourier-transform infra-red (FTIR) spectroscopy also confirms that these materials consist of proteinic and poly/oligosaccharidic populations. These materials can emulsify stable oil–in–water emulsions at pH 3 for a few days, while the same emulsions collapse in less than 24 h at pH 7. Confocal microscopy and droplet size distribution data suggest that Ostwald ripening, rather than coalescence, is the major course of emulsion instability. The above point to a short-process alternative to full composting in producing a high added value product from solid olive processing waste.

The aim of this work was the study and evaluation of winery by-products in the framework of the circular bioeconomy. Grape seeds and grape skins from Greek Ionian Islands varieties were analyzed in an attempt to provide the appropriate basis for model development of their sustainable exploitation at a local or regional level. The by-products were collected directly from the wineries immediately after the vinification process and were analyzed by chromatographic and spectroscopic techniques. In addition, annual production and yields were estimated. Grape seed oil quality was evaluated based on fatty acid methyl ester (FAME) composition. The grape skins’ phenolic fraction was extracted by an eco-friendly, nontoxic water-glycerol solvent system and was detected qualitatively. In addition, total phenolic content (TPC) and antioxidant activity (ABTS, DPPH) were measured. Based on estimated yields, our results demonstrate that winery by-products have the potential to promote the cyclical bioeconomy in a modern economic growth model that will reduce by-products and environmental costs as they can be reused as whole material in foods, dietary supplements, cosmetic ingredients, food colorants, and preservatives.