# An Overview on Management and Valorisation of Winery Wastes
## 2 Winery Waste Composition and Source of Bio-Active Compounds  
Winemaking by-products contain high amounts of bioactive secondary metabolites from various phytochemical groups (alkaloids, antibiotics, phenolics, resins, saponins, sterols, tannins, terpen, and volatile oils) [19]. Table 1 presents the most abundant compounds from various by-products from winery waste. Figure 2: Grape pomace sources and potential applications. Therefore, these by-products can be further used for obtaining new products, such as food additives, animal feed, cosmetics, fertilizers, ingredients for foods/dietary supplements, medical remedies, nutraceuticalticals, antimicrobial components, or biomass for biofuels [21; 22]. Among the bioactive metabolites, polyphenols are one of the most abundant, representing around 70% of the bioactive components [23]. They can be classified into two major groups, based on their chemical structure, number of aromatic rings, and binding affinity: flavonoids and non-flavonoids [23]. Flavonoids from grapes are further divided into five subgroups: anthocyanins, alkenes, flavonoids, flavan-3-ols, and flavones [14]. Non-flavonoids comprise counarins, lignans, phenolic acids (hydroxybenzoic and hydroxcimanic acids), and stilbenes [23; 24]. The most abundant winemaking by-product is grape pomace (or grape marc), a solid organic material remaining after the crushing, draining, and pressing steps. It contains a mixture of grape seeds, skins, and stalks. It was estimated that from 6 L of wine, 1 kg of grape marc remains [21; 22]. The chemical composition of grape pomace is, however, influenced by the environment (climate and soil) [13; 25; 26], the viticultural factors (defoliation, fertilization, grape variety, maturity, or harvest time) [26], and by the used winemaking method [18]. One of the most important characteristics of grape pomace is the high polyphenic content, due to its pharmacological properties. The compounds responsible for these properties are the alcohols, anthocyanins, flavanols/catechins, flavonol glycosides, lignans, procyanidins, resveratrol, phenolic acids, and stilbenes [21; 25]. Grape skins are generally recognized as the major component of the grape marc, comprising up to 56% of the dry matter in red pomace, and 28% of the dry matter in white pomace [27]. The inner layer of the grape skins contains phenolics such as anthocyanins and tannins, but small amounts of gallates compared with other grape marc components [16]. Anthocyanins are mostly located in skins, the major compound being malvidin-3-O-glucose, followed by penoidin-3-O-glucoside. The skins also contain neutral polysaccharides (12% hemicelluloses and 20% cellulose), 20% acidic pectin compounds, 15% insoluble proanthocyanidins, 5% compounds soluble in dichloromethane, 5-12% structural proteins, and 2-8% ash [27; 28]. Another important winemaking by-product is represented by the grape seeds, corresponding to 38-50% of the grape marc on a dry matter basis and approximately 5% of the grape weight [29]. Every year, almost 3 megatonnes of grape seeds are globally \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Waste** & **Composition (_w/tv_)** & **Percentage (\%)** & **Ref.** \\ \hline \multirow{4}{*}{Leaves} & Anthocyanins & \multirow{4}{*}{N/A} \\  & Flavonols & & \\  & Organic acids & & \\  & Tannins & & \\ \hline \multirow{4}{*}{Seeds} & Essential oil & 16\% & \\  & Fibre & 40\% & \\  & Protein & 11\% & \\  & Phenolics & 7\% & \\ \hline \multirow{4}{*}{Stem} & Insoluble residues & 71\% & \\  & Moisture content & 55–80\% & \\  & Phenolics & 6\% & \\ \hline \multirow{4}{*}{Pomace (marc)} & Cellulose & 27–75\% & \\  & Lignin & 17–24\% & \\ \cline{1-1}  & Moisture content & 50–70\% & \\ \cline{1-1}  & Protein & \textless{4\%} & \\ \hline \multirow{4}{*}{Lees} & Dead yeast & \multirow{4}{*}{N/A} \\  & Grape pulp & & \\ \cline{1-1}  & Inorganic matter & & \\ \cline{1-1}  & Phenolics & & \\ \cline{1-1}  & Tartaric acid & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main characteristics of the by-products.