White grape pomace (cv Fiano) as plant alternative ingredient in food industry: Stability of functional components of milled white pomace

• Effect of storage condition and grain size on WPF polyphenol content has been tested. • Bioactive content of WPF was stable after six months storage at 4°C in the dark. • GPF with granulometry ≤ 200 μm shows the best polyphenols content and stability. The possibility of reusing white grape pomace as ingredient in food formulations requires investigation on the effect of storage time and temperature after milling to obtain flour. Stability of antioxidant activity, total phenol content and composition, fatty acid composition, and color of whole white pomace flour with two granulometries (≤ 200 μm and ≤ 500 μm) during six months storage period, at two different temperatures (4°C and 25°C) in the dark, were analysed. Both total polyphenol content and antioxidant activity remain comparable to the starting sample. Molecules such as oenin, caftaric acid, cutaric acid and catechin show a clear reduction during storage, mostly at 25°C. Storage at 4°C is more efficient in ensuring polyphenol stability. Similar results were obtained for the stability of fatty acids at 4°C pointing out the importance of low temperature for lipid preservation. Grape pomace flour with granulometry ≤ 200 μm shows the best results of polyphenols content and stability, however both granulometries showed similar antioxidant activity. These results demonstrate the stability of health-relevant bioactive compounds, during six months storage, and define the best storage conditions of white grape pomace flour supporting the reuse of white pomace as alternative plant food ingredient in food formulations.