Pretreatment/fractionation and characterization of winery waste streams within an integrated biorefinery concept

The aim of this work was the characterization of the main winery wastes, e.g. vineyard prunings, grape stalks, grape pomace and wine lees, and the utilization of the hydrothermal pretreatment towards selective fractionation and recovery of hemicellulose (and related sugars, furans and acids), increased cellulose enzymatic hydrolysis, and isolation of “surface” and hydrothermal/acid hydrolysis lignin, discussing also the potential valorization of each stream into value-added chemicals. Two varieties from Greece were investigated, i.e. Grenache Rouge (Vitis vinifera L. cv. Grenache Rouge) and Malagouzia (Vitis vinifera L. cv. Malagouzia). Three hydrothermal pretreatment severities were applied, i.e. logRo 3.24, 4.32 and 4.71 (corresponding to 170^oC-15 min, 170^oC-180 min, and 220^oC-15 min), all leading to enhanced enzymatic hydrolysis of cellulose in the vine prunings to glucose. The composition of the recovered aqueous product contained mainly glucan and xylan, which were converted to monomeric sugars and eventually to furans (furfural, HMF) and organic acids (formic, lactic) at more intense conditions. The grape stalks and mainly the grape pomace which comprises of grape skins and seeds, contained less carbohydrates compared to vine prunings, but can be considered as an abundant source of lignin that can provide fast pyrolysis oils enriched in phenolic compounds. Similarly, the extracted surface lignin from the hydrothermally pretreated vine prunings may offer highly phenolic/aromatic bio-oils. The extractives of the parent lignocellulosic wastes (15–50 wt%) contain water soluble sugar monomers and oligo-saccharides and ethanol soluble fatty acids (palmitic, tridecanoic, a-linoleic, oleic, stearic acids). The wine lees can be considered as a source of value-added polyols and phenyl alcohols, such as glycerin (1,2,3-propanotriol), 2,3-butanediol and phenylethyl alcohol.