## 4 Conclusions  
The GPP, used for bread fortification (up a level of 10% \(w/w\)), was characterized by 39 anthocyanins, 10 flaxan-3-ols, 31 flavones and derivatives, 36 flavonoids, 28 low-molecular-weight phenolics (tyrosol derivatives), and 44 phenolic acids (mainly hydroxycinnamics). The greatest content in phenolic compounds was recorded for the G10 sample being 127.76 mg/100 g DM. The fortification with GPP determined a great increase of anthocyanins (recording 35.82 mg/100 g DM in GP10) whose bioaccessibility, after in vitro digestion, increased when moving from the gastric to the small intestine phase with an average value of 24%. Moreover, the increasing level of GPP in bread determined a decrease in the starch hydrolysis and in the predicted glycemic index. These results together with the data that we previously reported regarding the technological and sensorial aspects indicate that GPP can be used as valuable ingredient to produce value-added wheat bread.  
**Supplementary Materials:** The following are available online at [[https://www.mdpi.com/2304-8](https://www.mdpi.com/2304-8)]([https://www.mdpi.com/2304-8](https://www.mdpi.com/2304-8)) 158/10/3/507/s1, Table S1: (a) Phenolic profile by UHPLC-QTOF of the GPP; (b) free and bound phenolic contents as mg/g of the GPP; (c) free and bound phenolic contents as mg/g of the different bread samples; (d) phenolic profile by UHPLC-QTOF of the different bread samples during in vitro digestion; (e) validation parameters and VIP discriminant compounds of the OPLS-DA models considering the digestion process; (f) Compounds structurally confirmed by UHPLC-QTOF-MSMS experiments, using the annotations provided by the QC samples; (g) Representative total ion current (TIC) chromatograms and extracted ion current plots for some GP10 phenolics when considering gastric and small intestine phases of in vitro gastrointestinal digestion.  
**Author Contributions:** Conceptualization, C.R., G.G., B.S.; methodology, M.C., [PERSON] ([PERSON]), F.B., software, [PERSON] ([PERSON]); formal analysis, [PERSON] ([PERSON]), G.G.; investigation, L.L.; resources, B.S.; data curation, [PERSON] ([PERSON]), L.L.; writing--original draft preparation, [PERSON] ([PERSON]), G.G., C.R., B.S.; writing--review and editing, L.L., B.S.; visualization, G.G., C.R.; supervision, B.S.; project administration, B.S.; funding acquisition, B.S. All authors have read and agreed to the published version of the manuscript.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Bread Sample** & **HI** & **pGI** \\ \hline GP0 & 100.00 \(\pm\) 0.00 a & 94.20 \(\pm\) 0.00 a \\ GP5 & 93.57 \(\pm\) 0.62 b & 88.86 \(\pm\) 0.54 b \\ GP10 & 86.45 \(\pm\) 2.30 c & 82.72 \(\pm\) 1.98 c \\ \hline \hline \end{tabular}
\end{table}
Table 3: Hydrolysis index (HI) and predicted glycemic index (pGI) of control bread (GP0) and bread fortified with different percentages of grape pomace powder (GP5: 5 g/100 g GPP; and GP10:10 g/100 g GPP). Values are expressed as mean \(\pm\) standard deviation.  
Funding: This research was funded by FSE 1695-0016-1463-2019 and JP 2018 (CUP B34 ID18000050003). Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Acknowledgments: The authors wish to thank the \"Romeo ed Enrica Invernizzi\" Foundation for supporting the metabolomic facility. Conflicts of Interest: The authors declare no conflict of interest.