# An Overview on Management and Valorisation of Winery Wastes
## 2 Winery Waste Composition and Source of Bio-Active Compounds
From Table 2 it can be deduced that the minimum inhibitory concentrations vary extensively, indicating that not only the resistance or sensitivity of the target bacteria, but that other various factors that affect the type and concentration of the extract phenolics also affect their antimicrobial activity. The antimicrobial activity of winemaking by-products can be influenced by various factors, such as the extraction solvent or procedure, grape variety, or pomace fraction [38; 40]. For instance, various studies reported that acetone/water/acetic acid extracts had higher  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Grape Variety** & **Country** & **By-Product** & \begin{tabular}{c} **Extraction** \\ **Method** \\ \end{tabular}  & \ \begin{tabular}{c} **Bio-Application** \\ **Gram Negative** \\ \end{tabular}  & \begin{tabular}{c} **MIC Range** \\ **(mg/L)** \\ \end{tabular}  & **Ref** \\ \hline \multicolumn{2}{c}{Cabermet Franc} & & & & & & 4.7–75.0 \\ \hline \multicolumn{2}{c}{Chambourcin} & \multirow{2}{*}{USA} & \multirow{2}{*}{Pomace} & Acetone/water & \multirow{2}{*}{_L. monocytogenes_} & \multirow{2}{*}{-} & 18.8–75.0 & \multirow{2}{*}{[37]} \\ \cline{2-2} \cline{5-6} \multicolumn{2}{c}{Vidal Blanc} & & & (80:20) & & & 15.6–250.0 & \multirow{2}{*}{[37]} \\ \cline{2-2} \cline{5-6} \multicolumn{2}{c}{Viognier} & & & & & 5.1–40.6 & & \\ \hline \multirow{2}{*}{Merlot} & \multirow{4}{*}{Brazil} & \multirow{4}{*}{Pomace} & SFE-ethanol & \multirow{2}{*}{_B. cereus_} & \multirow{2}{*}{_E. coli_} & 0.007–0.012 & \multirow{2}{*}{-} \\ \cline{3-3} \cline{5-6} \multicolumn{2}{c}{} & & SOX-hexane & & _S. aureus_ & & & - \\ \cline{3-3} \cline{5-6} \multirow{2}{*}{Syrah} & & & & & & \(\,\  
inhibitory activity compared to methanol/water/acetic acid extracts [39]. Regarding the grape variety, some reports mentioned that winemaking by-products resulting from red grapes had a higher minimum inhibitory concentration than those resulting from white grapes [19]. Further investigation demonstrated that there is a connection between the phenolic content of the extracts obtained from various pomace fractions and their antibacterial properties [38]. Comparing some of these results, seeds can be considered as more appropriate sources of antibacterial extracts than other fractions [35]. A potential antimicrobial application of polyphenolic extracts resulting from winemaking by-products is as antibiotic adjuvants [44]. Their potential as multidrug resistance inhibitors may enhance the activity of the antibiotics [44]. However, the mechanism of plant polyphenols-antibiotic synergism is still unclear Although there seem to be four principal steps: (a) active site modification on and in the bacterial cell [45]; (b) inhibition of bacterial enzymes that affect antibiotic modification or degradation [46]; (c) increasing membrane permeability [45]; and (d) inhibition of the antibiotic outflow pumps [45]. An in vitro study against clinical multidrug-resistant strains of E. coli and S. aureus highlighted the synergism between grape pomace extracts and some antibiotics [47]. The discovery of in vitro bioactivity is the first step on a long and difficult road in terms of drug development. Various factors must be taken into consideration: bioavailability, mode of delivery, toxicity, and the interaction with other compounds [44]. Furthermore, overcoming the actual lack of knowledge on the synergistic properties of the winemaking by-products and their mechanisms of interaction with the bacteria or antibiotics represents an important milestone [48]. Grape Pomace as Antioxidant and Anti-Inflammatory Agents, Dietary Fibre, or as Ingredi in Food Products  
The grape pomace is usually discarded by the wineries or is used as compost or animal feed without any pre-treatment [49], although there is an increasing trend for finding new food sources or ingredients with nutritional and functional characteristics [50].