Gamma irradiation as a grape pomace stabilisation treatment: Assessment of phenolic and mineral preservation

Grape pomace is a winery by-product whose valorisation requires stabilisation strategies to preserve quality during storage. This study assessed gamma irradiation (gamma-IR) as a non-thermal treatment for two commercial grape pomace matrices, unfermented ‘Sauvignon blanc’ (SBP) and fermented ‘Malbec’ pomaces. Samples were exposed to 0–2000 Gy and analysed after 1 and 30 days for phenolic stability, mineral composition, and mineral–phenolic relationships. Effects depended on dose, matrix, and storage. Doses of 500–1000 Gy preserved phenolics with minor mineral changes, whereas higher doses increased phenolic losses. At day 30, non-coloured phenolics in SBP varied by less than 16% from day-1 levels at 500–1000 Gy but decreased by 31% at 2000 Gy. DPPH antioxidant capacity declined by 39–52% in SBP and 8–49% in Malbec pomace. In SBP, the initial bacterial reduction was not sustained after 30 days of refrigerated storage. Exploratory correlations suggested mineral–phenolic associations. Overall, gamma-IR shows promise as a matrix-specific pretreatment.