## 3 Results and Discussion  
### Stability of Polyphenols in Negroamaro Pomace Flour Extracts during Storage  
GPF stored for six months in the dark at 4 and 25 \({}^{\circ}\)C, showed no significant differences in total anthocyanin and oenin content (Table 1). In the chromatographic profile of the GPF extracts, we detected phenolic acids such as caffe, caftaric, cutaric and gallic acids and these metabolites had a similar relative distribution during storage (Table 1). Stilbenes content, and in particular resveratrol, shows significant differences among _V. vinifera_ cultivars [20]. Table 1 shows the results related to the analysis of stilbene levels in Negroamaro GPF. It can be seen that trans-resveratrol levels increase during the six months storage period, both at 4 \({}^{\circ}\)C and 25 \({}^{\circ}\)C.  
In grape, flavanols can be found as monomers (epicatechin 3-gallate, gallocatechin, euggallocatechin and epicatechin), oligomers and polymers (i.e., tannins and proanthocyanidins) that show antioxidant activity both in vitro and in vivo [21; 22; 23]. In this study we identified the flavanols catechhin and epicatechin in GPF (Table 1). While storage at 4 \({}^{\circ}\)C did not affect their content significantly, we observed a slight but statistically significant decrease following storage for six months at 25 \({}^{\circ}\)C.  
Flavonols are considered bioactive grape/wine compounds that are potentially relevant for human health and nutrition [24; 25]. Moreover, in a process known as co-pigmentation anthocyanins can interact with flavonoids, leading to an increase in red color. In our GPF we identified the flavonoids quercetin and quercetin 3-glycos (Table 1). In this study GPF prolonged storage do not affect flavonoids content. Conversely, the concentration of other compounds such as stilbenes increased over time. This later is in agreement with other studies of food ingredients, that reported a storage-related increase in phenol content [26; 27]. Storage can lead to changes in plant and cell tissue structure, as well as degradation of covalently bound phenolic molecules. In turn, that lead to an increase in solubility and consequently an improved extraction of such compounds. These results confirmed the hypothesis that GPF can be stored at both 4 \({}^{\circ}\)C and 25 \({}^{\circ}\)C without losing of several of its biological properties. Assessment of Total Phenols and Antioxidant Activity of GPF during Storage at Different Temperatures  
During six months, at 28-day intervals, we monitored variations in the concentration of phenolic compounds present in GPF using the Folin Ciocalteu assay. The obtained results indicated that the total phenol content in grape flour does not change significantly throughout the entire period either at 4 \({}^{\circ}\)C or 25 \({}^{\circ}\)C (Figure 1) remaining comparable to the control sample (T0). Total antioxidant activity (AA) was determined using the TEAC/ABTS\({}^{\star+}\) assay. This assay, despite its limitations mainly due to the steric accessibility of ABTS\({}^{\star+}\), has been and still is used to monitor changes in antioxidant activity during food processing or storage, as the sample components with antioxidant activity are constant. We observed no significant changes in antioxidant activity across all timepoints analyzed during the six month storage period. The above findings highlighted a correlation with the stability of different polyphenol groups (in Table 1), and their synergic activity (Figure 2). \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Time** & **Anthocyanans** & **Oenin** & **Caffeic Acid** & **Caffaric** & **Cataic Acid** & **Gallic Acid** & **Trans-** & **Catechin** & **Epicatechin** & **Quercetin** & **Querc.